makefile复制代码java.lang.OutOfMemoryError: Java heap space

makefile复制代码java.lang.OutOfMemoryError: PermGen space
java.lang.OutOfMemoryError: Metaspace

bash复制代码java.lang.OutOfMemoryError：GC overhead limit exceeded

csharp复制代码public class JVMStackSOF {
    private int stacklength = 1;   // 记录栈深度

    // 调用这个递归方法以造成栈溢出
    public void stackPush(){
        stacklength++;
        stackPush();
    }
    public static void main(String[] args) throws Throwable{
        JVMStackSOF sof = new JVMStackSOF();
        try{
            sof.stackPush();
        }catch(Throwable e){
            System.out.println("stack length = " + sof.stacklength);
            throw e;
        }
    }
}

arduino复制代码openjdk@ubuntu:~$ java -Xss256k -cp
/home/openjdk/NetBeansProjects/JavaApplication1/build/classes test_JVMStackSOF.JVMStackSOF
stack length = 1888
Exception in thread "main" java.lang.StackOverflowError
   at test_JVMStackSOF.JVMStackSOF.stackPush(JVMStackSOF.java:17)
   at test_JVMStackSOF.JVMStackSOF.stackPush(JVMStackSOF.java:18)

typescript复制代码public class JVMStackOOM {

    private void dontStop() {
        while (true) {
        }
    }

    public static void main(String[] args) {
        // 不断开启新的线程消耗虚拟机栈空间
        while (true) {
            new Thread(new Runnable() {
                @Override
                public void run() {
                    dontStop();
                }
            }).start();
        }
    }
}

sql复制代码java.lang.OutOfMemoryError : unable to create new native Thread

bash复制代码/proc/sys/kernel/pid_max
/proc/sys/kernel/thread-max
max_user_process（ulimit -u）
/proc/sys/vm/max_map_count

arduino复制代码java.lang.OutOfMemoryError: Requested array size exceeds VM limit

makefile复制代码java.lang.OutOfMemoryError: Out of swap space

makefile复制代码java.lang.OutOfMemoryError: stack_trace_with_native_method

java复制代码import java.nio.ByteBuffer;
import java.util.ArrayList;
import java.util.List;
public class DirectBufferOom {
  public static void main(String[] args) {
    final int _1M = 1024 * 1024;
    List<ByteBuffer> buffers = new ArrayList<>();
    int count = 1;
    while (true) {
      ByteBuffer byteBuffer = ByteBuffer.allocateDirect(_1M);
      buffers.add(byteBuffer);
      System.out.println(count++);
    }
  }
}

less复制代码Exception in thread "main" java.lang.OutOfMemoryError: Direct buffer memory
    at java.nio.Bits.reserveMemory(Bits.java:695)
    at java.nio.DirectByteBuffer.<init>(DirectByteBuffer.java:123)
    at java.nio.ByteBuffer.allocateDirect(ByteBuffer.java:311)
    at DirectBufferOom.main(DirectBufferOom.java:12)

java复制代码import sun.misc.Unsafe;

import java.lang.reflect.Field;

public class UnsafeOom {
  private static final int _1M = 1024 * 1024;

  public static void main(String[] args) throws IllegalAccessException, NoSuchFieldException {
    Field unsafeField = Unsafe.class.getDeclaredField("theUnsafe");
    unsafeField.setAccessible(true);
    Unsafe unsafe = (Unsafe) unsafeField.get(null);
    while (true) {
      unsafe.allocateMemory(_1M);
    }
  }
}

arduino复制代码Exception in thread"main"java.lang.OutOfMemoryError
at sun.misc.Unsafe.allocateMemory（Native Method）
at org.fenixsoft.oom.DMOOM.main（DMOOM.java：20）

sql复制代码CREATE TABLE `user` (
  `id` int(11) NOT NULL,
  `user_id` int(8) DEFAULT NULL COMMENT '用户id',
  `user_name` varchar(29) DEFAULT NULL COMMENT '用户名',
  `user_introduction` varchar(498) DEFAULT NULL COMMENT '用户介绍',
  `sex` tinyint(1) DEFAULT NULL COMMENT '性别',
  `age` int(3) DEFAULT NULL COMMENT '年龄',
  `birthday` date DEFAULT NULL COMMENT '生日',
  PRIMARY KEY (`id`),
  KEY `index_un_age_sex` (`user_name`,`age`,`sex`),
  KEY `index_age_sex` (`age`,`sex`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

sql复制代码select user_id, user_name, user_introduction from user where age > 20 and age < 50

ini复制代码public int lengthOfLongestSubstring(String s) {
        int maxLen = 0;
        for(int i = 0; i < s.length(); i++){
          // 创建一个存放字符的集合
            HashSet<Character> set = new HashSet<>();
            for(int j = i; j < s.length(); j++) {
              // 判断集合是否存在第 j 个字符
                if(set.contains(s.charAt(j)))
                    break;
                set.add(s.charAt(j));
            }
            maxLen = Math.max(maxLen,set.size());
        }
        return maxLen;
    }

ini复制代码    public boolean add(E e) {
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            Object[] elements = getArray();
            int len = elements.length;
            Object[] newElements = Arrays.copyOf(elements, len + 1);
            newElements[len] = e;
            setArray(newElements);
            return true;
        } finally {
            lock.unlock();
        }
    }

kotlin复制代码    public E get(int index) {
        return get(getArray(), index);
    }

    @SuppressWarnings("unchecked")
    private E get(Object[] a, int index) {
        return (E) a[index];
    }

csharp复制代码public interface UserService {
    public void addUser(User user);
    public User getUser(int id);
}

csharp复制代码public class UserServiceImpl implements UserService {
    public void addUser(User user) {
        System.out.println("add user into database.");
    }
    public User getUser(int id) {
        User user = new User();
        user.setId(id);
        System.out.println("getUser from database.");
        return user;
    }
}

typescript复制代码public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    System.out.println("do sth before....");
    Object result =  method.invoke(target, args);
    System.out.println("do sth after....");
    return result;
}
ProxyUtil(Object target){
    this.target = target;
}
public Object getTarget() {
    return target;
}
public void setTarget(Object target) {
    this.target = target;
}

scss复制代码    // 生成代理对象，对被代理对象的这些接口进行代理：UserServiceImpl.class.getInterfaces()
    UserService proxyObject = (UserService) Proxy.newProxyInstance(Thread.currentThread().getContextClassLoader(), 
                UserServiceImpl.class.getInterfaces(), proxyUtils);
    proxyObject.getUser(1);
    proxyObject.addUser(new User());
}

java复制代码package net.aazj.aop;

import java.lang.reflect.Method;
import net.sf.cglib.proxy.Enhancer;
import net.sf.cglib.proxy.MethodInterceptor;
import net.sf.cglib.proxy.MethodProxy;

public class CGProxy implements MethodInterceptor{
    private Object target;    // 被代理对象
    public CGProxy(Object target){
        this.target = target;
    }
    public Object intercept(Object arg0, Method arg1, Object[] arg2, MethodProxy proxy) throws Throwable {
        System.out.println("do sth before....");
        Object result = proxy.invokeSuper(arg0, arg2);
        System.out.println("do sth after....");
        return result;
    }
    public Object getProxyObject() {
        Enhancer enhancer = new Enhancer();
        enhancer.setSuperclass(this.target.getClass());    // 设置父类
        // 设置回调
        enhancer.setCallback(this);    // 在调用父类方法时，回调 this.intercept()
        // 创建代理对象
        return enhancer.create();
    }
}

java复制代码public class CGProxyTest {
    public static void main(String[] args){
        Object proxyedObject = new UserServiceImpl();    // 被代理的对象
        CGProxy cgProxy = new CGProxy(proxyedObject);
        UserService proxyObject = (UserService) cgProxy.getProxyObject();
        proxyObject.getUser(1);
        proxyObject.addUser(new User());
    }
}

erlang复制代码do sth before....
getUser from database.
do sth after....
do sth before....
add user into database.
do sth after....

arduino复制代码@SuppressWarnings("serial")
public class DefaultAopProxyFactory implements AopProxyFactory, Serializable {
    @Override
    public AopProxy createAopProxy(AdvisedSupport config) throws AopConfigException {
        if (config.isOptimize() || config.isProxyTargetClass() || hasNoUserSuppliedProxyInterfaces(config)) {
            Class<?> targetClass = config.getTargetClass();
            if (targetClass == null) {
                throw new AopConfigException("TargetSource cannot determine target class: " +
                        "Either an interface or a target is required for proxy creation.");
            }
            if (targetClass.isInterface()) {
                return new JdkDynamicAopProxy(config);
            }
            return new ObjenesisCglibAopProxy(config);
        }
        else {
            return new JdkDynamicAopProxy(config);
        }
    }

arduino复制代码if (targetClass.isInterface()) {
                return new JdkDynamicAopProxy(config);
            }
            return new ObjenesisCglibAopProxy(config);

kotlin复制代码final class JdkDynamicAopProxy implements AopProxy, InvocationHandler, Serializable {    
    @Override
    public Object getProxy(ClassLoader classLoader) {
        if (logger.isDebugEnabled()) {
            logger.debug("Creating JDK dynamic proxy: target source is " + this.advised.getTargetSource());
        }
        Class<?>[] proxiedInterfaces = AopProxyUtils.completeProxiedInterfaces(this.advised);
        findDefinedEqualsAndHashCodeMethods(proxiedInterfaces);
        return Proxy.newProxyInstance(classLoader, proxiedInterfaces, this);
    }

ini复制代码    <tx:advice id="transactionAdvice" transaction-manager="transactionManager"?>
        <tx:attributes >
            <tx:method name="add*" propagation="REQUIRED" />
            <tx:method name="append*" propagation="REQUIRED" />
            <tx:method name="insert*" propagation="REQUIRED" />
            <tx:method name="save*" propagation="REQUIRED" />
            <tx:method name="update*" propagation="REQUIRED" />
    
            <tx:method name="get*" propagation="SUPPORTS" />
            <tx:method name="find*" propagation="SUPPORTS" />
            <tx:method name="load*" propagation="SUPPORTS" />
            <tx:method name="search*" propagation="SUPPORTS" />
    
            <tx:method name="*" propagation="SUPPORTS" />
        </tx:attributes>
    </tx:advice>
    <aop:config>
        <aop:pointcut id="transactionPointcut" expression="execution(* net.aazj.service..*Impl.*(..))" />
        <aop:advisor pointcut-ref="transactionPointcut" advice-ref="transactionAdvice" />
    </aop:config>

ini复制代码    <bean id="aspectBean" class="net.aazj.aop.DataSourceInterceptor"/>
    <aop:config>
        <aop:aspect id="dataSourceAspect" ref="aspectBean">
            <aop:pointcut id="dataSourcePoint" expression="execution(public * net.aazj.service..*.getUser(..))" />
            <aop:pointcut expression="" id=""/>
            <aop:before method="before" pointcut-ref="dataSourcePoint"/>
            <aop:after method=""/>
            <aop:around method=""/>
        </aop:aspect>
        
        <aop:aspect></aop:aspect>
    </aop:config>

csharp复制代码<aop:aspect> 配置一个切面；<aop:pointcut>配置一个切点，基于切点表达式；<aop:before>,<aop:after>,<aop:around>是定义不同类型的advise. aspectBean 是切面的处理bean：

public class DataSourceInterceptor {
    public void before(JoinPoint jp) {
        DataSourceTypeManager.set(DataSources.SLAVE);
    }
}

xml复制代码
    <!-- 使用annotation定义事务 -->
    <tx:annotation-driven transaction-manager="transactionManager" />

ini复制代码    <context:component-scan base-package="net.aazj.service,net.aazj.aop" />

java复制代码@Service("userService")
@Transactional
public class UserServiceImpl implements UserService{
    @Autowired
    private UserMapper userMapper;
    
    @Transactional (readOnly=true)
    public User getUser(int userId) {
        System.out.println("in UserServiceImpl getUser");
        System.out.println(DataSourceTypeManager.get());
        return userMapper.getUser(userId);
    }
    
    public void addUser(String username){
        userMapper.addUser(username);
//        int i = 1/0;    // 测试事物的回滚
    }
    
    public void deleteUser(int id){
        userMapper.deleteByPrimaryKey(id);
//        int i = 1/0;    // 测试事物的回滚
    }
    
    @Transactional (rollbackFor = BaseBusinessException.class)
    public void addAndDeleteUser(String username, int id) throws BaseBusinessException{
        userMapper.addUser(username);
        this.m1();
        userMapper.deleteByPrimaryKey(id);
    }
    
    private void m1() throws BaseBusinessException {
        throw new BaseBusinessException("xxx");
    }

    public int insertUser(User user) {
        return this.userMapper.insert(user);
    }
}

ini复制代码<context:component-scan base-package="net.aazj.aop" />

makefile复制代码<aop:aspectj-autoproxy />

kotlin复制代码import org.aspectj.lang.JoinPoint;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Before;
import org.aspectj.lang.annotation.Pointcut;
import org.springframework.core.annotation.Order;
import org.springframework.stereotype.Component;
@Aspect    // for aop
@Component // for auto scan
@Order(0)  // execute before @Transactional
public class DataSourceInterceptor {
    @Pointcut("execution(public * net.aazj.service..*.get*(..))")
    public void dataSourceSlave(){};
    
    @Before("dataSourceSlave()")
    public void before(JoinPoint jp) {
        DataSourceTypeManager.set(DataSources.SLAVE);
    }
}

less复制代码/**
 * Annotation that defines ordering. The value is optional, and represents order value
 * as defined in the {@link Ordered} interface. Lower values have higher priority.
 * The default value is {@code Ordered.LOWEST_PRECEDENCE}, indicating
 * lowest priority (losing to any other specified order value).
 */
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE, ElementType.METHOD, ElementType.FIELD})
public @interface Order {
    /**
     * The order value. Default is {@link Ordered#LOWEST_PRECEDENCE}.
     * @see Ordered#getOrder()
     */
    int value() default Ordered.LOWEST_PRECEDENCE;
}

scss复制代码within(net.aazj.service.*)， within(net.aazj.service..*)，within(net.aazj.service.UserServiceImpl.*)

scss复制代码this(net.aazj.service.UserService): 实现了UserService的代理对象(中的所有方法)；

target(net.aazj.service.UserService): 被代理对象实现了UserService(中的所有方法)；

less复制代码@within(org.springframework.transaction.annotation.Transactional)
@target(org.springframework.transaction.annotation.Transactional)

java复制代码@Aspect
@Component // for auto scan
//@Order(2)
public class LogInterceptor {    
    @Pointcut("execution(public * net.aazj.service..*.getUser(..))")
    public void myMethod(){};
    
    @Before("myMethod()")
    public void before() {
        System.out.println("method start");
    } 
    
    @After("myMethod()")
    public void after() {
        System.out.println("method after");
    } 
    
    @AfterReturning("execution(public * net.aazj.mapper..*.*(..))")
    public void AfterReturning() {
        System.out.println("method AfterReturning");
    } 
    
    @AfterThrowing("execution(public * net.aazj.mapper..*.*(..))")
//  @Around("execution(public * net.aazj.mapper..*.*(..))")
    public void AfterThrowing() {
        System.out.println("method AfterThrowing");
    } 
    
    @Around("execution(public * net.aazj.mapper..*.*(..))")
    public Object Around(ProceedingJoinPoint jp) throws Throwable {
        System.out.println("method Around");
        SourceLocation sl = jp.getSourceLocation();
        Object ret = jp.proceed();
        System.out.println(jp.getTarget());
        return ret;
    } 
    
    @Before("execution(public * net.aazj.service..*.getUser(..)) && args(userId,..)")
    public void before3(int userId) {
        System.out.println("userId-----" + userId);
    }  
    
    @Before("myMethod()")
    public void before2(JoinPoint jp) {
        Object[] args = jp.getArgs();
        System.out.println("userId11111: " + (Integer)args[0]);
        System.out.println(jp.getTarget());
        System.out.println(jp.getThis());
        System.out.println(jp.getSignature());
        System.out.println("method start");
    }    
}

java复制代码    @Before("execution(public * net.aazj.service..*.getUser(..)) && args(userId,..)")
    public void before3(int userId) {
        System.out.println("userId-----" + userId);
    }

typescript复制代码@Service("userService")
@Transactional
public class UserServiceImpl implements UserService{
    @Autowired
    private UserMapper userMapper;
    
    @Transactional (readOnly=true)
    public User getUser(int userId) {
        return userMapper.getUser(userId);
    }
    
    public void addUser(String username){
        getUser(2);
        userMapper.addUser(username);
    }

java复制代码@Aspect
@Component
public class AOPTest {
    @Before("execution(public * net.aazj.service..*.getUser(..))")
    public void m1(){
        System.out.println("in m1...");
    }    
    @Before("execution(public * net.aazj.service..*.addUser(..))")
    public void m2(){
        System.out.println("in m2...");
    }
}

typescript复制代码public class Test {
    public static void main(String[] args){        
        ApplicationContext context = new ClassPathXmlApplicationContext(
                        new String[]{"config/spring-mvc.xml","config/applicationContext2.xml"});

        UserService us = context.getBean("userService", UserService.class);
        if(us != null){
            us.addUser("aaa");

erlang复制代码in m2...

ini复制代码<aop:aspectj-autoproxy expose-proxy="true"/>

typescript复制代码@Service("userService")
@Transactional
public class UserServiceImpl implements UserService{
    @Autowired
    private UserMapper userMapper;
    
    @Transactional (readOnly=true)
    public User getUser(int userId) {
        return userMapper.getUser(userId);
    }
    
    public void addUser(String username){
        ((UserService)AopContext.currentProxy()).getUser(2);
        userMapper.addUser(username);
    }

erlang复制代码in m2...
in m1...

java复制代码public static void main(String[] args) throws IOException, InterruptedException {
    List<Object> dataList = new ArrayList<>();
    for (int i = 0; i < 25; i++) {
        byte[] data = createData(1024 * 1024 * 40);// 40 MB
        dataList.add(data);
    }
    Thread.sleep(10000);
    dataList = null; // 待会 GC 直接回收
    for (int i = 0; i < 100; i++) {
        // 测试多次 GC
        System.gc();
        Thread.sleep(1000);
    }
    System.in.read();
}
public static byte[] createData(int size){
    byte[] data = new byte[size];
    for (int i = 0; i < size; i++) {
        data[i] = Byte.MAX_VALUE;
    }
    return data;
}

java复制代码Map<String, Object> map = new HashMap<>();
map.put("a", "first");

java复制代码/**
 * Constructs an empty <tt>HashMap</tt> with the default initial capacity
 * (16) and the default load factor (0.75).
 */
public HashMap() {
    this.loadFactor = DEFAULT_LOAD_FACTOR; // all other fields defaulted
}

java复制代码/**
 * Computes key.hashCode() and spreads (XORs) higher bits of hash
 * to lower.  Because the table uses power-of-two masking, sets of
 * hashes that vary only in bits above the current mask will
 * always collide. (Among known examples are sets of Float keys
 * holding consecutive whole numbers in small tables.)  So we
 * apply a transform that spreads the impact of higher bits
 * downward. There is a tradeoff between speed, utility, and
 * quality of bit-spreading. Because many common sets of hashes
 * are already reasonably distributed (so don't benefit from
 * spreading), and because we use trees to handle large sets of
 * collisions in bins, we just XOR some shifted bits in the
 * cheapest possible way to reduce systematic lossage, as well as
 * to incorporate impact of the highest bits that would otherwise
 * never be used in index calculations because of table bounds.
 */
static final int hash(Object key) {
    int h;
    return (key == null) ? 0 : (h = key.hashCode()) ^ (h >>> 16);
}

java复制代码/**
 * The default initial capacity - MUST be a power of two.
 */
static final int DEFAULT_INITIAL_CAPACITY = 1 << 4; // aka 16

java复制代码newCap = DEFAULT_INITIAL_CAPACITY;
Node<K,V>[] newTab = (Node<K,V>[])new Node[newCap];
table = newTab;

java复制代码/**
 * Basic hash bin node, used for most entries.  (See below for
 * TreeNode subclass, and in LinkedHashMap for its Entry subclass.)
 */
static class Node<K,V> implements Map.Entry<K,V> {
    final int hash;
    final K key;
    V value;
    Node<K,V> next;

    Node(int hash, K key, V value, Node<K,V> next) {
        this.hash = hash;
        this.key = key;
        this.value = value;
        this.next = next;
    }
    // 省略其他部分代码
}

java复制代码tab = table
tab[i] = newNode(hash, key, value, null);

java复制代码/**
 * Associates the specified value with the specified key in this map.
 * If the map previously contained a mapping for the key, the old
 * value is replaced.
 *
 * @param key key with which the specified value is to be associated
 * @param value value to be associated with the specified key
 * @return the previous value associated with <tt>key</tt>, or
 *         <tt>null</tt> if there was no mapping for <tt>key</tt>.
 *         (A <tt>null</tt> return can also indicate that the map
 *         previously associated <tt>null</tt> with <tt>key</tt>.)
 */
public V put(K key, V value) {
    return putVal(hash(key), key, value, false, true);
}

/**
 * Implements Map.put and related methods.
 *
 * @param hash hash for key
 * @param key the key
 * @param value the value to put
 * @param onlyIfAbsent if true, don't change existing value
 * @param evict if false, the table is in creation mode.
 * @return previous value, or null if none
 */
final V putVal(int hash, K key, V value, boolean onlyIfAbsent,
               boolean evict) {
    Node<K,V>[] tab; Node<K,V> p; int n, i;
    if ((tab = table) == null || (n = tab.length) == 0)
        // 初始化table
        n = (tab = resize()).length;
    if ((p = tab[i = (n - 1) & hash]) == null)
        // 目标位置上没有元素，直接将key-value封装成的Node放入数组
        tab[i] = newNode(hash, key, value, null);
    else {
        Node<K,V> e; K k;
        // 目标位置上有元素，则比较key值是否相等
        if (p.hash == hash &&
            ((k = p.key) == key || (key != null && key.equals(k))))
            // key值相等
            e = p;
        else if (p instanceof TreeNode)
            e = ((TreeNode<K,V>)p).putTreeVal(this, tab, hash, key, value);
        else {
            // key值不相等
            for (int binCount = 0; ; ++binCount) {
                if ((e = p.next) == null) {
                    // 遍历链表，找到链表的最后一个节点，将新的元素插入到链表的尾部（尾插法）
                    p.next = newNode(hash, key, value, null);
                    if (binCount >= TREEIFY_THRESHOLD - 1) // -1 for 1st
                        // 判断是否需要将链表转成红黑树
                        treeifyBin(tab, hash);
                    break;
                }
                if (e.hash == hash &&
                    ((k = e.key) == key || (key != null && key.equals(k))))
                    break;
                // 链表继续遍历
                p = e;
            }
        }
        if (e != null) { // existing mapping for key
            // 目标位置上有key值相等的元素，将新的value覆盖旧的value
            V oldValue = e.value;
            if (!onlyIfAbsent || oldValue == null)
                e.value = value;
            afterNodeAccess(e);
            return oldValue;
        }
    }
    ++modCount;
    if (++size > threshold)
        // 数组扩容
        resize();
    afterNodeInsertion(evict);
    return null;
}

java复制代码/**
 * Returns the value to which the specified key is mapped,
 * or {@code null} if this map contains no mapping for the key.
 *
 * <p>More formally, if this map contains a mapping from a key
 * {@code k} to a value {@code v} such that {@code (key==null ? k==null :
 * key.equals(k))}, then this method returns {@code v}; otherwise
 * it returns {@code null}.  (There can be at most one such mapping.)
 *
 * <p>A return value of {@code null} does not <i>necessarily</i>
 * indicate that the map contains no mapping for the key; it's also
 * possible that the map explicitly maps the key to {@code null}.
 * The {@link #containsKey containsKey} operation may be used to
 * distinguish these two cases.
 *
 * @see #put(Object, Object)
 */
public V get(Object key) {
    Node<K,V> e;
    return (e = getNode(hash(key), key)) == null ? null : e.value;
}

/**
 * Implements Map.get and related methods.
 *
 * @param hash hash for key
 * @param key the key
 * @return the node, or null if none
 */
final Node<K,V> getNode(int hash, Object key) {
    Node<K,V>[] tab; Node<K,V> first, e; int n; K k;
    if ((tab = table) != null && (n = tab.length) > 0 &&
        (first = tab[(n - 1) & hash]) != null) {
        // 找到hash值在数组位置上的元素
        if (first.hash == hash && // always check first node
            ((k = first.key) == key || (key != null && key.equals(k))))
            // 比较key值是否相等
            return first;
        if ((e = first.next) != null) {
            if (first instanceof TreeNode)
                return ((TreeNode<K,V>)first).getTreeNode(hash, key);
            do {
                // 遍历链表
                if (e.hash == hash &&
                    ((k = e.key) == key || (key != null && key.equals(k))))
                    return e;
            } while ((e = e.next) != null);
        }
    }
    return null;
}

java复制代码import lombok.extern.slf4j.Slf4j;

@Slf4j
public class DemoTest {

    public static void main(String[] args) throws Exception {
        long beginTime = System.currentTimeMillis();
        int processA = new InterfaceA().process();
        int processB = new InterfaceB().process();
        int result = processA + processB;
        log.info("执行结果：{} 耗时：{}", result, System.currentTimeMillis() - beginTime);
    }

    @Slf4j
    public final static class InterfaceA {
        Integer result = 1;

        public int process() {
            long beginTime = System.currentTimeMillis();
            try {
                Thread.sleep(2000);
            } catch (Exception e) {
                log.error("InterfaceA.process Exception");
            }
            log.info("执行接口InterfaceA.process 耗时：{}ms", System.currentTimeMillis() - beginTime);
            return result;
        }
    }

    @Slf4j
    public final static class InterfaceB {
        Integer result = 1;

        public int process() {
            long beginTime = System.currentTimeMillis();
            try {
                Thread.sleep(2000);
            } catch (Exception e) {
                log.error("InterfaceB.process Exception");
            }
            log.info("执行接口InterfaceB.process 耗时：{}ms", System.currentTimeMillis() - beginTime);
            return result;
        }
    }
}

ini复制代码21:40:17.603 [main] INFO DemoTest$InterfaceA - 执行接口InterfaceA.process 耗时：2002ms
21:40:19.612 [main] INFO DemoTest$InterfaceB - 执行接口InterfaceB.process 耗时：2001ms
21:40:19.613 [main] INFO DemoTest - 执行结果：2 耗时：4018

java复制代码import cn.hutool.core.thread.ThreadFactoryBuilder;
import lombok.extern.slf4j.Slf4j;

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.Future;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;

@Slf4j
public class DemoTest {
    private static ThreadPoolExecutor pool = new ThreadPoolExecutor(
            5,
            5,
            60,
            TimeUnit.SECONDS,
            new ArrayBlockingQueue<Runnable>(1000),
            ThreadFactoryBuilder.create().setNamePrefix("线程名称-").build()
    );

    public static void main(String[] args) throws Exception {
        long beginTime = System.currentTimeMillis();

        List<Future<Integer>> futures = new ArrayList<>(2);
        List<Integer> results = new ArrayList<>(2);
        futures.add(pool.submit(() -> new InterfaceA().process()));
        futures.add(pool.submit(() -> new InterfaceB().process()));
        for (Future<Integer> item : futures) {
            results.add(item.get());
        }
        
        int result = results.get(0) + results.get(1);
        log.info("执行结果：{} 耗时：{}", result, System.currentTimeMillis() - beginTime);
    }

    @Slf4j
    public final static class InterfaceA {
        Integer result = 1;

        public int process() {
            long beginTime = System.currentTimeMillis();
            try {
                Thread.sleep(2000);
            } catch (Exception e) {
                log.error("InterfaceA.process Exception");
            }
            log.info("执行接口InterfaceA.process 耗时：{}ms", System.currentTimeMillis() - beginTime);
            return result;
        }
    }

    @Slf4j
    public final static class InterfaceB {
        Integer result = 1;

        public int process() {
            long beginTime = System.currentTimeMillis();
            try {
                Thread.sleep(2000);
            } catch (Exception e) {
                log.error("InterfaceB.process Exception");
            }
            log.info("执行接口InterfaceB.process 耗时：{}ms", System.currentTimeMillis() - beginTime);
            return result;
        }
    }
}

ini复制代码22:03:43.180 [线程名称-1] INFO DemoTest$InterfaceB - 执行接口InterfaceB.process 耗时：2004ms
22:03:43.180 [线程名称-0] INFO DemoTest$InterfaceA - 执行接口InterfaceA.process 耗时：2004ms
22:03:43.190 [main] INFO DemoTest - 执行结果：2 耗时：2020

java复制代码import com.google.common.collect.Lists;
import lombok.extern.slf4j.Slf4j;

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.CompletableFuture;

@Slf4j
public class DemoTest {

    public static void main(String[] args) throws Exception {
        long beginTime = System.currentTimeMillis();

        CompletableFuture<Integer> interfaceFuturesA = CompletableFuture.supplyAsync(() -> new InterfaceA().process());
        CompletableFuture<Integer> interfaceFuturesB = CompletableFuture.supplyAsync(() -> new InterfaceB().process());
        CompletableFuture<List<Integer>> future = CompletableFuture
                .allOf(interfaceFuturesA, interfaceFuturesB)
                .thenApply((none) -> {
                    List<Integer> dataList = new ArrayList<>(2);
                    try {
                        dataList.add(interfaceFuturesA.get());
                        dataList.add(interfaceFuturesB.get());
                    } catch (Exception e) {
                        log.error("执行异常");
                    }
                    return dataList;
                }).exceptionally(e -> Lists.newArrayList());

        int result = future.get().get(0) + future.get().get(1);
        log.info("执行结果：{} 耗时：{}", result, System.currentTimeMillis() - beginTime);
    }

    @Slf4j
    public final static class InterfaceA {
        Integer result = 1;

        public int process() {
            long beginTime = System.currentTimeMillis();
            try {
                Thread.sleep(2000);
            } catch (Exception e) {
                log.error("InterfaceA.process Exception");
            }
            log.info("执行接口InterfaceA.process 耗时：{}ms", System.currentTimeMillis() - beginTime);
            return result;
        }
    }

    @Slf4j
    public final static class InterfaceB {
        Integer result = 1;

        public int process() {
            long beginTime = System.currentTimeMillis();
            try {
                Thread.sleep(2000);
            } catch (Exception e) {
                log.error("InterfaceB.process Exception");
            }
            log.info("执行接口InterfaceB.process 耗时：{}ms", System.currentTimeMillis() - beginTime);
            return result;
        }
    }
}

ini复制代码22:31:44.822 [ForkJoinPool.commonPool-worker-5] INFO DemoTest$InterfaceB - 执行接口InterfaceB.process 耗时：2005ms
22:31:44.822 [ForkJoinPool.commonPool-worker-3] INFO DemoTest$InterfaceA - 执行接口InterfaceA.process 耗时：2002ms
22:31:44.831 [main] INFO DemoTest - 执行结果：2 耗时：2027

java复制代码@Intercepts(
        {@org.apache.ibatis.plugin.Signature(
                type = Executor.class, 
                method = "query", 
                args = {MappedStatement.class, Object.class, RowBounds.class, ResultHandler.class})})
public class DefaultInterceptor implements Interceptor {

    private Logger logger = LoggerFactory.getLogger(this.getClass());


    @Override
    public Object intercept(Invocation invocation) throws Throwable {
        logger.info("------> this is in intercept <-------");
        return invocation.proceed();
    }

    @Override
    public Object plugin(Object target) {
        logger.info("------> this is in plugin <-------");
        return Plugin.wrap(target, this);
    }

    @Override
    public void setProperties(Properties properties) {
        logger.info("------> this is in setProperties <-------");
    }
}

java复制代码@Configuration
public class PluginsConfig {

    @Autowired
    private List<SqlSessionFactory> sqlSessionFactoryList;

    @PostConstruct
    public void addPageInterceptor() {
        DefaultInterceptor interceptor = new DefaultInterceptor();
        // 此处往 SqlSessionFactory 中添加
        for (SqlSessionFactory sqlSessionFactory : sqlSessionFactoryList) {
            sqlSessionFactory.getConfiguration().addInterceptor(interceptor);
        }
    }
}

java复制代码
M- Interceptor#intercept(Invocation invocation) : 拦截方法
M- plugin : 调用 Plugin#wrap(Object target, Interceptor interceptor) 方法，执行代理对象的创建
M- setProperties : 从 properties 获取一些需要的属性值

// 这里可以看到 , 其中强制实现的方法只有 intercept


public interface Interceptor {

  Object intercept(Invocation invocation) throws Throwable;

  default Object plugin(Object target) {
    return Plugin.wrap(target, this);
  }

  default void setProperties(Properties properties) {
  }

}

java复制代码// 主要的大纲如此所示
F- List<Interceptor> ArrayList
M- addInterceptor : 添加拦截器
    - 在 Configuration 的 #pluginElement(XNode parent) 方法中被调用
        - 创建 Interceptor 对象，并调用 Interceptor#setProperties(properties) 方法
        - 调用 Configuration#addInterceptor(interceptorInstance) 方法
        - 添加到 Configuration.interceptorChain 中
M- pluginAll : 应用所有拦截器到指定目标对象

java复制代码
// 步骤一 : 声明拦截器对象
@Intercepts(
        {@org.apache.ibatis.plugin.Signature(
                type = Executor.class, 
                method = "query", 
                args = {MappedStatement.class, Object.class, RowBounds.class, ResultHandler.class})})
                
                
//  步骤二 : sqlSessionFactory 中添加拦截器对象
sqlSessionFactory.getConfiguration().addInterceptor(interceptor);

java复制代码C01- Configuration
    F01_01- InterceptorChain interceptorChain
    M01_01- addInterceptor
        - interceptorChain.addInterceptor(interceptor)
                ?- 可以看到 , 这里往 InterceptorChain 添加了 interceptor
                
// M01_01 源代码            
public void addInterceptor(Interceptor interceptor) {
    interceptorChain.addInterceptor(interceptor);
}



public class InterceptorChain {

  private final List<Interceptor> interceptors = new ArrayList<Interceptor>();

  public Object pluginAll(Object target) {
    for (Interceptor interceptor : interceptors) {
      target = interceptor.plugin(target);
    }
    return target;
  }

  // 可以看到 , 这里将拦截器加到了拦截器链中
  // PS : 但是此处未完全完成 , 仅仅只是添加 , 具体的操作会在上面 pluginAll 中完成
  public void addInterceptor(Interceptor interceptor) {
    interceptors.add(interceptor);
  }
  
  public List<Interceptor> getInterceptors() {
    return Collections.unmodifiableList(interceptors);
  }

}

java复制代码
public static SqlSession getSqlSession(SqlSessionFactory sessionFactory, ExecutorType executorType, PersistenceExceptionTranslator exceptionTranslator) {

    notNull(sessionFactory, NO_SQL_SESSION_FACTORY_SPECIFIED);
    notNull(executorType, NO_EXECUTOR_TYPE_SPECIFIED);

    SqlSessionHolder holder = (SqlSessionHolder) TransactionSynchronizationManager.getResource(sessionFactory);

    SqlSession session = sessionHolder(executorType, holder);
    if (session != null) {
      return session;
    }
    
    // 核心节点 , 开启 Session
    session = sessionFactory.openSession(executorType);

    registerSessionHolder(sessionFactory, executorType, exceptionTranslator, session);

    return session;
  }

java复制代码C- DefaultSqlSessionFactory
// 打开的起点 : 打开 session 的时候 , 
  private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) {
    Transaction tx = null;
    try {
      final Environment environment = configuration.getEnvironment();
      final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);
      tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);
      
      // 此处构建 Executor 并且放入 Session
      final Executor executor = configuration.newExecutor(tx, execType);
      return new DefaultSqlSession(configuration, executor, autoCommit);
    } catch (Exception e) {
      closeTransaction(tx); // may have fetched a connection so lets call close()
      throw ExceptionFactory.wrapException("Error opening session.  Cause: " + e, e);
    } finally {
      ErrorContext.instance().reset();
    }
  }


// 调用拦截链
C- Configuration
public Executor newExecutor(Transaction transaction, ExecutorType executorType) {
    executorType = executorType == null ? defaultExecutorType : executorType;
    executorType = executorType == null ? ExecutorType.SIMPLE : executorType;
    Executor executor;
    if (ExecutorType.BATCH == executorType) {
      executor = new BatchExecutor(this, transaction);
    } else if (ExecutorType.REUSE == executorType) {
      executor = new ReuseExecutor(this, transaction);
    } else {
      executor = new SimpleExecutor(this, transaction);
    }
    if (cacheEnabled) {
      executor = new CachingExecutor(executor);
    }
    // 此处调用拦截链 , 构建 Executor 对象
    executor = (Executor) interceptorChain.pluginAll(executor);
    return executor;
}

// 拦截链处理
C- InterceptorChain
  public Object pluginAll(Object target) {
    // 此处是在构建拦截器链 , 返回的是最后的拦截器处理类  
    for (Interceptor interceptor : interceptors) {
      target = interceptor.plugin(target);
    }
    return target;
  }


C- Plugin
// 调用 Plugin wrap , 生成了一个新的 plugin , 该 plugin 包含对应的 interceptor 的 拦截方法
  public static Object wrap(Object target, Interceptor interceptor) {
    Map<Class<?>, Set<Method>> signatureMap = getSignatureMap(interceptor);
    Class<?> type = target.getClass();
    Class<?>[] interfaces = getAllInterfaces(type, signatureMap);
    if (interfaces.length > 0) {
      // 核心 , 对方法做了代理 , 同时为代理类传入了 Plugin  
      return Proxy.newProxyInstance(
          type.getClassLoader(),
          interfaces,
          new Plugin(target, interceptor, signatureMap));
    }
    return target;
  }

java复制代码public interface Executor {

  ResultHandler NO_RESULT_HANDLER = null;

  int update(MappedStatement ms, Object parameter) throws SQLException;

  <E> List<E> query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey cacheKey, BoundSql boundSql) throws SQLException;

  <E> List<E> query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler) throws SQLException;

  <E> Cursor<E> queryCursor(MappedStatement ms, Object parameter, RowBounds rowBounds) throws SQLException;

  List<BatchResult> flushStatements() throws SQLException;

  void commit(boolean required) throws SQLException;

  void rollback(boolean required) throws SQLException;

  CacheKey createCacheKey(MappedStatement ms, Object parameterObject, RowBounds rowBounds, BoundSql boundSql);

  boolean isCached(MappedStatement ms, CacheKey key);

  void clearLocalCache();

  void deferLoad(MappedStatement ms, MetaObject resultObject, String property, CacheKey key, Class<?> targetType);

  Transaction getTransaction();

  void close(boolean forceRollback);

  boolean isClosed();

  void setExecutorWrapper(Executor executor);

}

java复制代码// 1 . 选择合适的 plugin
C- DefaultSqlSession
  public <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds) {
    try {
      MappedStatement ms = configuration.getMappedStatement(statement);
      return executor.query(ms, wrapCollection(parameter), rowBounds, Executor.NO_RESULT_HANDLER);
    } catch (Exception e) {
      throw ExceptionFactory.wrapException("Error querying database.  Cause: " + e, e);
    } finally {
      ErrorContext.instance().reset();
    }
  }

// 2 . 中间通过 proxy 代理
    

// 3 . plugin 中调用拦截器
C05- Plugin
    F05_01- private final Interceptor interceptor;
    M05_01- invoke(Object proxy, Method method, Object[] args)
		- 获取可以拦截的 method
		- 判断当前的 method 是否在可拦截的
		
        
// M05_01 : invoke@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    try {
        Set<Method> methods = signatureMap.get(method.getDeclaringClass());
        if (methods != null && methods.contains(method)) {
            // 此处调用了拦截器
            return interceptor.intercept(new Invocation(target, method, args));
        }
        return method.invoke(target, args);
    } catch (Exception e) {
        throw ExceptionUtil.unwrapThrowable(e);
    }
}

// 4 . 调用 interceptor
public Object intercept(Invocation invocation) throws Throwable {
    // 此处调用代理方法的实际逻辑
    return invocation.proceed();
}

java复制代码@Intercepts(
        {
                @Signature(type = Executor.class, method = "query", args = {MappedStatement.class, Object.class, RowBounds.class, ResultHandler.class}),
                @Signature(type = Executor.class, method = "query", args = {MappedStatement.class, Object.class, RowBounds.class, ResultHandler.class, CacheKey.class, BoundSql.class}),
        }
)
public class PageInterceptor implements Interceptor {
    private volatile Dialect dialect;
    private String countSuffix = "_COUNT";
    protected Cache<String, MappedStatement> msCountMap = null;
    private String default_dialect_class = "com.github.pagehelper.PageHelper";

    @Override
    public Object intercept(Invocation invocation) throws Throwable {
        try {
            Object[] args = invocation.getArgs();
            
            // 获取请求的四个参数
            MappedStatement ms = (MappedStatement) args[0];
            Object parameter = args[1];
            RowBounds rowBounds = (RowBounds) args[2];
            ResultHandler resultHandler = (ResultHandler) args[3];
            Executor executor = (Executor) invocation.getTarget();
            CacheKey cacheKey;
            BoundSql boundSql;
            //由于逻辑关系，只会进入一次
            if (args.length == 4) {
                //4 个参数时
                // 获取绑定 SQL : select id, type_code, type_class, type_policy, type_name, supplier_id, supplier_name from sync_type
                boundSql = ms.getBoundSql(parameter);
                cacheKey = executor.createCacheKey(ms, parameter, rowBounds, boundSql);
            } else {
                //6 个参数时
                cacheKey = (CacheKey) args[4];
                boundSql = (BoundSql) args[5];
            }
            checkDialectExists();

            List resultList;
            //调用方法判断是否需要进行分页，如果不需要，直接返回结果
            if (!dialect.skip(ms, parameter, rowBounds)) {
                //判断是否需要进行 count 查询
                if (dialect.beforeCount(ms, parameter, rowBounds)) {
                    //查询总数
                    Long count = count(executor, ms, parameter, rowBounds, resultHandler, boundSql);
                    //处理查询总数，返回 true 时继续分页查询，false 时直接返回
                    if (!dialect.afterCount(count, parameter, rowBounds)) {
                        //当查询总数为 0 时，直接返回空的结果
                        return dialect.afterPage(new ArrayList(), parameter, rowBounds);
                    }
                }
                resultList = ExecutorUtil.pageQuery(dialect, executor,
                        ms, parameter, rowBounds, resultHandler, boundSql, cacheKey);
            } else {
                //rowBounds用参数值，不使用分页插件处理时，仍然支持默认的内存分页
                resultList = executor.query(ms, parameter, rowBounds, resultHandler, cacheKey, boundSql);
            }
            return dialect.afterPage(resultList, parameter, rowBounds);
        } finally {
            dialect.afterAll();
        }
    }

    /**
     * Spring bean 方式配置时，如果没有配置属性就不会执行下面的 setProperties 方法，就不会初始化
     * <p>
     * 因此这里会出现 null 的情况 fixed #26
     */
    private void checkDialectExists() {
        if (dialect == null) {
            synchronized (default_dialect_class) {
                if (dialect == null) {
                    setProperties(new Properties());
                }
            }
        }
    }

    private Long count(Executor executor, MappedStatement ms, Object parameter,
                       RowBounds rowBounds, ResultHandler resultHandler,
                       BoundSql boundSql) throws SQLException {
        String countMsId = ms.getId() + countSuffix;
        Long count;
        //先判断是否存在手写的 count 查询
        MappedStatement countMs = ExecutorUtil.getExistedMappedStatement(ms.getConfiguration(), countMsId);
        if (countMs != null) {
            count = ExecutorUtil.executeManualCount(executor, countMs, parameter, boundSql, resultHandler);
        } else {
            countMs = msCountMap.get(countMsId);
            //自动创建
            if (countMs == null) {
                //根据当前的 ms 创建一个返回值为 Long 类型的 ms
                countMs = MSUtils.newCountMappedStatement(ms, countMsId);
                msCountMap.put(countMsId, countMs);
            }
            count = ExecutorUtil.executeAutoCount(dialect, executor, countMs, parameter, boundSql, rowBounds, resultHandler);
        }
        return count;
    }

    @Override
    public Object plugin(Object target) {
        return Plugin.wrap(target, this);
    }

    @Override
    public void setProperties(Properties properties) {
        //缓存 count ms
        msCountMap = CacheFactory.createCache(properties.getProperty("msCountCache"), "ms", properties);
        String dialectClass = properties.getProperty("dialect");
        if (StringUtil.isEmpty(dialectClass)) {
            dialectClass = default_dialect_class;
        }
        try {
            Class<?> aClass = Class.forName(dialectClass);
            dialect = (Dialect) aClass.newInstance();
        } catch (Exception e) {
            throw new PageException(e);
        }
        dialect.setProperties(properties);

        String countSuffix = properties.getProperty("countSuffix");
        if (StringUtil.isNotEmpty(countSuffix)) {
            this.countSuffix = countSuffix;
        }
    }

}

java复制代码/**
* 执行自动生成的 count 查询
**/
public static Long executeAutoCount(Dialect dialect, Executor executor, MappedStatement countMs,
                                        Object parameter, BoundSql boundSql,
                                        RowBounds rowBounds, ResultHandler resultHandler) throws SQLException {
        Map<String, Object> additionalParameters = getAdditionalParameter(boundSql);
        //创建 count 查询的缓存 key
        CacheKey countKey = executor.createCacheKey(countMs, parameter, RowBounds.DEFAULT, boundSql);
        // 调用方言获取 count sql
        // SELECT count(0) FROM sync_type
        String countSql = dialect.getCountSql(countMs, boundSql, parameter, rowBounds, countKey);
        //countKey.update(countSql);
        BoundSql countBoundSql = new BoundSql(countMs.getConfiguration(), countSql, boundSql.getParameterMappings(), parameter);
        //当使用动态 SQL 时，可能会产生临时的参数，这些参数需要手动设置到新的 BoundSql 中
        for (String key : additionalParameters.keySet()) {
            countBoundSql.setAdditionalParameter(key, additionalParameters.get(key));
        }
        //执行 count 查询
        Object countResultList = executor.query(countMs, parameter, RowBounds.DEFAULT, resultHandler, countKey, countBoundSql);
        Long count = (Long) ((List) countResultList).get(0);
        return count;
}

java复制代码public static  <E> List<E> pageQuery(Dialect dialect, Executor executor, MappedStatement ms, Object parameter,
                                 RowBounds rowBounds, ResultHandler resultHandler,
                                 BoundSql boundSql, CacheKey cacheKey) throws SQLException {
        //判断是否需要进行分页查询
        if (dialect.beforePage(ms, parameter, rowBounds)) {
            //生成分页的缓存 key
            CacheKey pageKey = cacheKey;
            //处理参数对象 , 此处生成分页的参数
            parameter = dialect.processParameterObject(ms, parameter, boundSql, pageKey);
            //调用方言获取分页 sql
            String pageSql = dialect.getPageSql(ms, boundSql, parameter, rowBounds, pageKey);
            BoundSql pageBoundSql = new BoundSql(ms.getConfiguration(), pageSql, boundSql.getParameterMappings(), parameter);

            Map<String, Object> additionalParameters = getAdditionalParameter(boundSql);
            //设置动态参数
            for (String key : additionalParameters.keySet()) {
                pageBoundSql.setAdditionalParameter(key, additionalParameters.get(key));
            }
            //执行分页查询
            return executor.query(ms, parameter, RowBounds.DEFAULT, resultHandler, pageKey, pageBoundSql);
        } else {
            //不执行分页的情况下，也不执行内存分页
            return executor.query(ms, parameter, RowBounds.DEFAULT, resultHandler, cacheKey, boundSql);
        }
}

java复制代码PageHelper.startPage(page, size);
List<SyncType> allOrderPresentList = syncTypeDAO.findAll();

// Step 1 : startPage 核心代码
public static <E> Page<E> startPage(int pageNum, int pageSize, boolean count, Boolean reasonable, Boolean pageSizeZero) {
        Page<E> page = new Page<E>(pageNum, pageSize, count);
        page.setReasonable(reasonable);
        page.setPageSizeZero(pageSizeZero);
        //当已经执行过orderBy的时候
        Page<E> oldPage = getLocalPage();
        if (oldPage != null && oldPage.isOrderByOnly()) {
            page.setOrderBy(oldPage.getOrderBy());
        }
        setLocalPage(page);
        return page;
}

此处最核心的就是 setLocalPage , 会使用 ThreadLocal 保持线程参数
protected static final ThreadLocal<Page> LOCAL_PAGE = new ThreadLocal<Page>();

// Step 2 : 拦截器中的参数获取
// 可以看到第一句就是从 getLocalPage - ThreadLocal 中获取
C- AbstractHelperDialect # processParameterObject

public Object processParameterObject(MappedStatement ms, Object parameterObject, BoundSql boundSql, CacheKey pageKey) {
        //处理参数
        Page page = getLocalPage();
        //如果只是 order by 就不必处理参数
        if (page.isOrderByOnly()) {
            return parameterObject;
        }
        Map<String, Object> paramMap = null;
        if (parameterObject == null) {
            paramMap = new HashMap<String, Object>();
        } else if (parameterObject instanceof Map) {
            //解决不可变Map的情况
            paramMap = new HashMap<String, Object>();
            paramMap.putAll((Map) parameterObject);
        } else {
            paramMap = new HashMap<String, Object>();
            //动态sql时的判断条件不会出现在ParameterMapping中，但是必须有，所以这里需要收集所有的getter属性
            //TypeHandlerRegistry可以直接处理的会作为一个直接使用的对象进行处理
            boolean hasTypeHandler = ms.getConfiguration().getTypeHandlerRegistry().hasTypeHandler(parameterObject.getClass());
            MetaObject metaObject = MetaObjectUtil.forObject(parameterObject);
            //需要针对注解形式的MyProviderSqlSource保存原值
            if (!hasTypeHandler) {
                for (String name : metaObject.getGetterNames()) {
                    paramMap.put(name, metaObject.getValue(name));
                }
            }
            //下面这段方法，主要解决一个常见类型的参数时的问题
            if (boundSql.getParameterMappings() != null && boundSql.getParameterMappings().size() > 0) {
                for (ParameterMapping parameterMapping : boundSql.getParameterMappings()) {
                    String name = parameterMapping.getProperty();
                    if (!name.equals(PAGEPARAMETER_FIRST)
                            && !name.equals(PAGEPARAMETER_SECOND)
                            && paramMap.get(name) == null) {
                        if (hasTypeHandler
                                || parameterMapping.getJavaType().equals(parameterObject.getClass())) {
                            paramMap.put(name, parameterObject);
                            break;
                        }
                    }
                }
            }
        }
        return processPageParameter(ms, paramMap, page, boundSql, pageKey);
}

bash复制代码{
  "$schema": "http://json.schemastore.org/launchsettings.json",
  "profiles": {
    "Net5ByDocker": {
      "commandName": "Project",
      "launchBrowser": true,
      "launchUrl": "swagger",
      "environmentVariables": {
        "ASPNETCORE_ENVIRONMENT": "Development"
      },
      "dotnetRunMessages": "true",
      "applicationUrl": "http://localhost:5000"
    }
  }
}