txt复制代码sessionId | reqType | Content-Length | Content |

xml复制代码<dependency>
    <groupId>io.netty</groupId>
    <artifactId>netty-all</artifactId>
</dependency>
<dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>slf4j-log4j12</artifactId>
</dependency>
<dependency>
    <groupId>org.projectlombok</groupId>
    <artifactId>lombok</artifactId>
</dependency>

java复制代码@Data
public class Header{
    private long sessionId; //会话id  : 占8个字节
    private byte type; //消息类型： 占1个字节

    private int length;     //消息长度 : 占4个字节
}

java复制代码@Data
public class MessageRecord{

    private Header header;
    private Object body;
}

java复制代码public enum OpCode {

    BUSI_REQ((byte)0),
    BUSI_RESP((byte)1),
    PING((byte)3),
    PONG((byte)4);

    private byte code;

    private OpCode(byte code) {
        this.code=code;
    }

    public byte code(){
        return this.code;
    }
}

java复制代码@Slf4j
public class MessageRecordEncoder extends MessageToByteEncoder<MessageRecord> {

    @Override
    protected void encode(ChannelHandlerContext channelHandlerContext, MessageRecord record, ByteBuf byteBuf) throws Exception {
        log.info("===========开始编码Header部分===========");
        Header header=record.getHeader();
        byteBuf.writeLong(header.getSessionId()); //保存8个字节的sessionId
        byteBuf.writeByte(header.getType());  //写入1个字节的请求类型

        log.info("===========开始编码Body部分===========");
        Object body=record.getBody();
        if(body!=null){
            ByteArrayOutputStream bos=new ByteArrayOutputStream();
            ObjectOutputStream oos=new ObjectOutputStream(bos);
            oos.writeObject(body);
            byte[] bytes=bos.toByteArray();
            byteBuf.writeInt(bytes.length); //写入消息体长度:占4个字节
            byteBuf.writeBytes(bytes); //写入消息体内容
        }else{
            byteBuf.writeInt(0); //写入消息长度占4个字节，长度为0
        }
    }
}

java复制代码@Slf4j
public class MessageRecordDecode extends ByteToMessageDecoder {

    @Override
    protected void decode(ChannelHandlerContext channelHandlerContext, ByteBuf byteBuf, List<Object> list) throws Exception {
        MessageRecord record=new MessageRecord();
        Header header=new Header();
        header.setSessionId(byteBuf.readLong());  //读取8个字节的sessionid
        header.setType(byteBuf.readByte()); //读取一个字节的操作类型
        record.setHeader(header);
        //如果byteBuf剩下的长度还有大于4个字节，说明body不为空
        if(byteBuf.readableBytes()>4){
            int length=byteBuf.readInt(); //读取四个字节的长度
            header.setLength(length);
            byte[] contents=new byte[length];
            byteBuf.readBytes(contents,0,length);
            ByteArrayInputStream bis=new ByteArrayInputStream(contents);
            ObjectInputStream ois=new ObjectInputStream(bis);
            record.setBody(ois.readObject());
            list.add(record);
            log.info("序列化出来的结果："+record);
        }else{
            log.error("消息内容为空");
        }
    }
}

java复制代码public class CodesMainTest {
    public static void main( String[] args ) throws Exception {
        EmbeddedChannel channel=new EmbeddedChannel(
            new LoggingHandler(),
            new MessageRecordEncoder(),
            new MessageRecordDecode());
        Header header=new Header();
        header.setSessionId(123456);
        header.setType(OpCode.PING.code());
        MessageRecord record=new MessageRecord();
        record.setBody("Hello World");
        record.setHeader(header);
        channel.writeOutbound(record);

        ByteBuf buf= ByteBufAllocator.DEFAULT.buffer();
        new MessageRecordEncoder().encode(null,record,buf);
        channel.writeInbound(buf);
    }
}

txt复制代码         +-------------------------------------------------+
         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 00 00 00 00 00 01 e2 40 03 00 00 00 12 ac ed 00 |.......@........|
|00000010| 05 74 00 0b 48 65 6c 6c 6f 20 57 6f 72 6c 64    |.t..Hello World |
+--------+-------------------------------------------------+----------------+

java复制代码public class CodesMainTest {
    public static void main( String[] args ) throws Exception {
        //EmbeddedChannel是netty专门针对ChannelHandler的单元测试而提供的类。可以通过这个类来测试channel输入入站和出站的实现
        EmbeddedChannel channel=new EmbeddedChannel(
                //解决粘包和半包问题
//                new LengthFieldBasedFrameDecoder(2048,10,4,0,0),
                new LoggingHandler(),
                new MessageRecordEncoder(),
                new MessageRecordDecode());
        Header header=new Header();
        header.setSessionId(123456);
        header.setType(OpCode.PING.code());
        MessageRecord record=new MessageRecord();
        record.setBody("Hello World");
        record.setHeader(header);
        channel.writeOutbound(record);

        ByteBuf buf= ByteBufAllocator.DEFAULT.buffer();
        new MessageRecordEncoder().encode(null,record,buf);

       //*********模拟半包和粘包问题************//
        //把一个包通过slice拆分成两个部分
        ByteBuf bb1=buf.slice(0,7); //获取前面7个字节
        ByteBuf bb2=buf.slice(7,buf.readableBytes()-7); //获取后面的字节
        bb1.retain();

        channel.writeInbound(bb1);
        channel.writeInbound(bb2);
    }
}

txt复制代码2021-08-31 15:53:01,385 [io.netty.handler.logging.LoggingHandler]-[DEBUG] [id: 0xembedded, L:embedded - R:embedded] READ: 7B
         +-------------------------------------------------+
         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 00 00 00 00 00 01 e2                            |.......         |
+--------+-------------------------------------------------+----------------+
2021-08-31 15:53:01,397 [io.netty.handler.logging.LoggingHandler]-[DEBUG] [id: 0xembedded, L:embedded - R:embedded] READ COMPLETE
Exception in thread "main" io.netty.handler.codec.DecoderException: java.lang.IndexOutOfBoundsException: readerIndex(0) + length(8) exceeds writerIndex(7): UnpooledSlicedByteBuf(ridx: 0, widx: 7, cap: 7/7, unwrapped: PooledUnsafeDirectByteBuf(ridx: 0, widx: 31, cap: 256))

java复制代码public class CodesMainTest {
    public static void main( String[] args ) throws Exception {
        EmbeddedChannel channel=new EmbeddedChannel(
                //解决粘包和半包问题
                new LengthFieldBasedFrameDecoder(1024,
                        9,4,0,0),
                new LoggingHandler(),
                new MessageRecordEncoder(),
                new MessageRecordDecode());
        Header header=new Header();
        header.setSessionId(123456);
        header.setType(OpCode.PING.code());
        MessageRecord record=new MessageRecord();
        record.setBody("Hello World");
        record.setHeader(header);
        channel.writeOutbound(record);

        ByteBuf buf= ByteBufAllocator.DEFAULT.buffer();
        new MessageRecordEncoder().encode(null,record,buf);

       //*********模拟半包和粘包问题************//
        //把一个包通过slice拆分成两个部分
        ByteBuf bb1=buf.slice(0,7);
        ByteBuf bb2=buf.slice(7,buf.readableBytes()-7);
        bb1.retain();

        channel.writeInbound(bb1);
        channel.writeInbound(bb2);
    }
}

java复制代码2021-08-31 16:09:35,115 [com.netty.example.codec.MessageRecordDecode]-[INFO] 序列化出来的结果：MessageRecord(header=Header(sessionId=123456, type=3, length=18), body=Hello World)
2021-08-31 16:09:35,116 [io.netty.handler.logging.LoggingHandler]-[DEBUG] [id: 0xembedded, L:embedded - R:embedded] READ COMPLETE

java复制代码@Slf4j
public class ProtocolServer {

    public static void main(String[] args){
        EventLoopGroup boss = new NioEventLoopGroup();
        //2 用于对接受客户端连接读写操作的线程工作组
        EventLoopGroup work = new NioEventLoopGroup();
        ServerBootstrap b = new ServerBootstrap();
        b.group(boss, work)	//绑定两个工作线程组
            .channel(NioServerSocketChannel.class)	//设置NIO的模式
            // 初始化绑定服务通道
            .childHandler(new ChannelInitializer<SocketChannel>() {
                @Override
                protected void initChannel(SocketChannel sc) throws Exception {
                    sc.pipeline()
                        .addLast(
                        new LengthFieldBasedFrameDecoder(1024,
                                                         9,4,0,0))
                        .addLast(new MessageRecordEncoder())
                        .addLast(new MessageRecordDecode())
                        .addLast(new ServerHandler());
                }
            });
        ChannelFuture cf= null;
        try {
            cf = b.bind(8080).sync();
            log.info("ProtocolServer start success");
            cf.channel().closeFuture().sync();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }finally {
            work.shutdownGracefully();
            boss.shutdownGracefully();
        }
    }
}

java复制代码@Slf4j
public class ServerHandler extends ChannelInboundHandlerAdapter {

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        MessageRecord messageRecord=(MessageRecord)msg;
        log.info("server receive message:"+messageRecord);
        MessageRecord res=new MessageRecord();
        Header header=new Header();
        header.setSessionId(messageRecord.getHeader().getSessionId());
        header.setType(OpCode.BUSI_RESP.code());
        String message="Server Response Message!";
        res.setBody(message);
        header.setLength(message.length());
        ctx.writeAndFlush(res);
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        log.error("服务器读取数据异常");
        super.exceptionCaught(ctx, cause);
        ctx.close();
    }
}

java复制代码public class ProtocolClient {

    public static void main(String[] args) {
        //创建工作线程组
        EventLoopGroup group = new NioEventLoopGroup();
        Bootstrap b = new Bootstrap();
        b.group(group).channel(NioSocketChannel.class)
            .handler(new ChannelInitializer<SocketChannel>() {
                @Override
                public void initChannel(SocketChannel ch) throws Exception {
                    ch.pipeline().addLast(new LengthFieldBasedFrameDecoder(1024,
                                                                           9,4,0,0))
                        .addLast(new MessageRecordEncoder())
                        .addLast(new MessageRecordDecode())
                        .addLast(new ClientHandler());

                }
            });
        // 发起异步连接操作
        try {
            ChannelFuture future = b.connect(new InetSocketAddress("localhost", 8080)).sync();
            Channel c = future.channel();
            for (int i = 0; i < 500; i++) {
                MessageRecord message = new MessageRecord();
                Header header = new Header();
                header.setSessionId(10001);
                header.setType((byte) OpCode.BUSI_REQ.code());
                message.setHeader(header);
                String context="我是请求数据"+i;
                header.setLength(context.length());
                message.setBody(context);
                c.writeAndFlush(message);
            }
            //closeFuture().sync()就是让当前线程(即主线程)同步等待Netty server的close事件，Netty server的channel close后，主线程才会继续往下执行。closeFuture()在channel close的时候会通知当前线程。
            future.channel().closeFuture().sync();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }finally {
            group.shutdownGracefully();
        }
    }
}

java复制代码@Slf4j
public class ClientHandler extends ChannelInboundHandlerAdapter {
    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        MessageRecord record=(MessageRecord)msg;
        log.info("Client Receive message:"+record);
        super.channelRead(ctx, msg);
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        super.exceptionCaught(ctx, cause);
        ctx.close();
    }
}

c复制代码#include <stdio.h>

int main(int argc, const char * argv[]) {
    printf("Hello, World!\n");
  
  	printf("my Name is cxuan \n")
    
    printf("number = %d \n", number);
    
    return 0;
}

shell复制代码gcc -o hello hello.c

c复制代码// 这是一个单行注释

/* 多行注释用一行表示 */

/*
 	多行注释用多行表示
 	 	多行注释用多行表示
 	 	 	多行注释用多行表示
 	 	 	 	多行注释用多行表示

*/

c复制代码#include <stdio.h> 
int main(){
 int a = -5;
 printf("%d\n",a);
 
 unsigned int b = 6;
 printf("%d\n",b);
 
}

c复制代码long int lia;
long la;
long long lla;
short int sib;
short sb;
unsigned int uic;
unsigned uc;
unsigned long uld;
unsigned short usd;

c复制代码char a = 'x';
char b = 'y';

c复制代码#include <stdio.h>

int main(){
 char a = 'x';
 int b;
 b = 'y';
 
 printf("%d\n%d\n",a,b);
}

c复制代码#include <stdio.h>

int main(){

 float aboat = 2100.0;
 double abet = 2.14e9;
 long double dip = 5.32e-5;
 
 printf("%f\n", aboat);
 printf("%e\n", abet);
 printf("%Lf\n", dip);
 
}

c复制代码float toobig = 3.4E38 * 100.0f;printf("%e\n",toobig);

c复制代码float toosmall = 0.1234e-38/10;printf("%e\n", toosmall);

c复制代码330         /* 合法的 */315u        /* 合法的 */0xFeeL      /* 合法的 */048         /* 非法的：8 进制不能定义 8 */

c复制代码3.14159       /* 合法的 */314159E-5L    /* 合法的 */510E          /* 非法的：不完整的指数 */210f          /* 非法的：没有小数或指数 */

c复制代码#include <stdio.h>#define LENGTH 5#define WIDTH 10int main(){  int area = LENGTH * WIDTH;  printf("area = %d\n", area); }

c复制代码#include <stdio.h>int main(){  const int LENGTH = 10; const int WIDTH = 5;  int area; area = LENGTH * WIDTH;  printf("area = %d\n", area); }

sql复制代码------------------------
LATEST DETECTED DEADLOCK
------------------------
2021-11-10 17:03:10 0x7fb040672700
*** (1) TRANSACTION:
TRANSACTION 46913, ACTIVE 142 sec starting index read
mysql tables in use 1, locked 1
LOCK WAIT 4 lock struct(s), heap size 1136, 3 row lock(s), undo log entries 1
MySQL thread id 2997198, OS thread handle 140394973071104, query id 9145673 localhost root updating
update test_tb set stu_name = 'lisi' where stu_id = 1006
*** (1) WAITING FOR THIS LOCK TO BE GRANTED:
RECORD LOCKS space id 224 page no 4 n bits 80 index uk_stu_id of table `testdb`.`test_tb` trx id 46913 lock_mode X locks rec but not gap waiting
Record lock, heap no 7 PHYSICAL RECORD: n_fields 2; compact format; info bits 0
 0: len 4; hex 800003ee; asc     ;;
 1: len 4; hex 80000006; asc     ;;

*** (2) TRANSACTION:
TRANSACTION 46914, ACTIVE 103 sec starting index read
mysql tables in use 1, locked 1
4 lock struct(s), heap size 1136, 3 row lock(s), undo log entries 1
MySQL thread id 2997201, OS thread handle 140394971473664, query id 9145681 localhost root updating
update test_tb set age = 21  where stu_id = 1005
*** (2) HOLDS THE LOCK(S):
RECORD LOCKS space id 224 page no 4 n bits 80 index uk_stu_id of table `testdb`.`test_tb` trx id 46914 lock_mode X locks rec but not gap
Record lock, heap no 7 PHYSICAL RECORD: n_fields 2; compact format; info bits 0
 0: len 4; hex 800003ee; asc     ;;
 1: len 4; hex 80000006; asc     ;;

*** (2) WAITING FOR THIS LOCK TO BE GRANTED:
RECORD LOCKS space id 224 page no 4 n bits 80 index uk_stu_id of table `testdb`.`test_tb` trx id 46914 lock_mode X locks rec but not gap waiting
Record lock, heap no 6 PHYSICAL RECORD: n_fields 2; compact format; info bits 0
 0: len 4; hex 800003ed; asc     ;;
 1: len 4; hex 80000005; asc     ;;

*** WE ROLL BACK TRANSACTION (2)

# 以上为原文 下面增加个人分析
------------------------
LATEST DETECTED DEADLOCK
------------------------
2021-11-10 17:03:10 0x7fb040672700 #这里显示了最近一次发生死锁的日期和时间
*** (1) TRANSACTION: #死锁相关的第一个事务
TRANSACTION 46913, ACTIVE 142 sec starting index read
#这行表示事务id为46913，事务处于活跃状态142s，starting index read表示正在使用索引读取数据行
mysql tables in use 1, locked 1
#这行表示该事务正在使用1个表，且涉及锁的表有1个
LOCK WAIT 4 lock struct(s), heap size 1136, 3 row lock(s), undo log entries 1
#这行表示在等待4把锁，占用内存1136字节，涉及3行记录
MySQL thread id 2997198, OS thread handle 140394973071104, query id 9145673 localhost root updating
#这行表示该事务的线程ID信息，操作系统句柄信息，连接来源、用户
update test_tb set stu_name = 'lisi' where stu_id = 1006
#这行表示事务执行的最后一条SQL信息
*** (1) WAITING FOR THIS LOCK TO BE GRANTED: #事务1想要获取的锁
RECORD LOCKS space id 224 page no 4 n bits 80 index uk_stu_id of table `testdb`.`test_tb` trx id 46913 lock_mode X locks rec but not gap waiting
#这行信息表示等待的锁是一个record lock，空间id是224，页编号为4，大概位置在页的80位处，锁发生在表testdb.test_tb的uk_stu_id索引上，是一个X锁，但是不是gap lock，waiting表示正在等待锁
Record lock, heap no 7 PHYSICAL RECORD: n_fields 2; compact format; info bits 0
 0: len 4; hex 800003ee; asc     ;;
 1: len 4; hex 80000006; asc     ;;

*** (2) TRANSACTION: #死锁相关的第一个事务
TRANSACTION 46914, ACTIVE 103 sec starting index read
#这行表示事务2的id为46914，事务处于活跃状态103s
mysql tables in use 1, locked 1
#正在使用1个表，涉及锁的表有1个
4 lock struct(s), heap size 1136, 3 row lock(s), undo log entries 1
#涉及4把锁，3行记录
MySQL thread id 2997201, OS thread handle 140394971473664, query id 9145681 localhost root updating
#事务2的线程ID信息，操作系统句柄信息，连接来源、用户
update test_tb set age = 21  where stu_id = 1005
#第二个事务的SQL
*** (2) HOLDS THE LOCK(S): # 事务2持有的锁 正是事务1想要获取的锁
RECORD LOCKS space id 224 page no 4 n bits 80 index uk_stu_id of table `testdb`.`test_tb` trx id 46914 lock_mode X locks rec but not gap
Record lock, heap no 7 PHYSICAL RECORD: n_fields 2; compact format; info bits 0
 0: len 4; hex 800003ee; asc     ;;
 1: len 4; hex 80000006; asc     ;;

*** (2) WAITING FOR THIS LOCK TO BE GRANTED:
RECORD LOCKS space id 224 page no 4 n bits 80 index uk_stu_id of table `testdb`.`test_tb` trx id 46914 lock_mode X locks rec but not gap waiting
Record lock, heap no 6 PHYSICAL RECORD: n_fields 2; compact format; info bits 0
 0: len 4; hex 800003ed; asc     ;;
 1: len 4; hex 80000005; asc     ;;
#上面这部分是事务二正在等待的锁，从信息上看，等待的是同一个表，同一个索引，同一个page上的record lock X锁，但是heap no位置不同，即不同的行上的锁

*** WE ROLL BACK TRANSACTION (2) #表示事务2被回滚

sql复制代码# 查看参数是否开启
mysql> show variables like 'innodb_print_all_deadlocks';
+----------------------------+-------+
| Variable_name              | Value |
+----------------------------+-------+
| innodb_print_all_deadlocks | OFF   |
+----------------------------+-------+

# 开启innodb_print_all_deadlocks,此参数是全局参数，可以动态调整。记得要加入到配置文件中
mysql> set global innodb_print_all_deadlocks = 1;
Query OK, 0 rows affected (0.00 sec)

mysql> show variables like 'innodb_print_all_deadlocks';
+----------------------------+-------+
| Variable_name              | Value |
+----------------------------+-------+
| innodb_print_all_deadlocks | ON    |
+----------------------------+-------+

java复制代码@Aspect
public class PointCutExample {
    // 定义一个PointCut切点
    @Pointcut("execution(* com.spring.Aop..service.*.*(..))")
    public void businessService() {}
}

java复制代码@Aspect
public class AdviceExample {
    //定义一个advice通知
    @Before("com.spring.Aop.aspect.PointCutExample.businessService()")
    public void before(JoinPoint joinPoint) {
        log.info("准备执行方法:{},参数列表:{}",joinPoint, Arrays.asList(joinPoint.getArgs()));
    }

xml复制代码 <!--目标对象一个普通bean-->
 <bean id="userServiceImpl" class="com.spring.Aop.service.。在上例中目标点就是UserServiceImpl类中的"></bean>

 <!--声明一个advice-->
 <bean id="logArgsAdvice" class="com.spring.Aop.aspect.LogArgsAdvice"></bean>

<aop:config>
    <!--定义切点-->
    <aop:pointcut id="logArgsPointCut" expression="execution(* com.spring.Aop..service.*.*(..))"></aop:pointcut>
     <!--定义advice通知-->
    <aop:aspect ref="logArgsAdvice">
        <aop:before method="before" pointcut-ref="logArgsPointCut"></aop:before>
    </aop:aspect>
</aop:config>

java复制代码//advice通知并没有加注解@AspectJ
public class LogArgsAdvice {

    public void before(JoinPoint joinPoint) throws Throwable {
      log.info("准备执行方法:{},参数列表:{}",joinPoint, Arrays.asList(joinPoint.getArgs()));
    }
}

typescript复制代码//UserService接口
public interface UserService {
   User createUser(String name,Integer age);
   User queryUser();
}
//UserServiceImpl实现类
@Slf4j
public class UserServiceImpl implements UserService {
    private static User user = null;

    @Override
    public User createUser(String name, Integer age) {
        user = new User();
        user.setName(name);
        user.setAge(age);
        log.info("UserServiceImpl createUser 方法执行中....");
        return user;
    }

    @Override
    public User queryUser() {
        log.info("UserServiceImpl queryUser 方法执行中....");
        return user;
    }
}

java复制代码// 定义PointCut
@Aspect
public class UserPointCut {

    @Pointcut("execution(* com.spring.Aop..service.*.*(..))")
    public void businessService() {}
}

less复制代码@Slf4j
@Aspect
public class UserAdvice {

    @Before("com.spring.Aop.aspect.UserPointCut.businessService()")
    public void before(JoinPoint joinPoint) {
        log.info("准备执行方法:{},参数列表:{}",joinPoint, Arrays.asList(joinPoint.getArgs()));
    }

    @AfterReturning(pointcut = "com.spring.Aop.aspect.UserPointCut.businessService()",returning="returnValue")
    public void afterReturning(JoinPoint joinPoint,Object returnValue){
        log.info("{}方法执行返回:{}",joinPoint,returnValue);
    }

xml复制代码<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns="http://www.springframework.org/schema/beans"
       xmlns:aop="http://www.springframework.org/schema/aop"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/aop
        http://www.springframework.org/schema/aop/spring-aop-2.0.xsd">
    <!--普通bean-->
    <bean id="userService" class="com.spring.Aop.service.UserServiceImpl"></bean>

    <!--定义advice通知-->
    <bean id="userAdvice" class="com.spring.Aop.aspect.UserAdvice"></bean>

    <!--开启@AspectJ配置-->
    <aop:aspectj-autoproxy/>

</beans>

ini复制代码ClassPathXmlApplicationContext applicationContext =  new ClassPathXmlApplicationContext("classpath:springAop-2.0aspectJ.xml");
UserService userService =  applicationContext.getBean(UserService.class);
userService.createUser("Jom",12);
userService.queryUser();

less复制代码//解析方法
@Override
@Nullable
public BeanDefinition parse(Element element, ParserContext parserContext) {
//注册类到Ioc容器
AopNamespaceUtils.registerAspectJAnnotationAutoProxyCreatorIfNecessary(parserContext, element);
   extendBeanDefinition(element, parserContext);
   return null;
}

scss复制代码public static void registerAspectJAnnotationAutoProxyCreatorIfNecessary(
      ParserContext parserContext, Element sourceElement) {
    //将一个类定义注册到IOC容器,并返回对象BeanDefinition
    //这个就是AnnotationAwareAspectJAutoProxyCreator.class
   BeanDefinition beanDefinition = AopConfigUtils.registerAspectJAnnotationAutoProxyCreatorIfNecessary(
         parserContext.getRegistry(), parserContext.extractSource(sourceElement));
   //处理proxy-target-class与expose-proxy属性,将beanDefinition对应的属性设置为true/false
   useClassProxyingIfNecessary(parserContext.getRegistry(), sourceElement);
   //注册组件
   registerComponentIfNecessary(beanDefinition, parserContext);
}

scss复制代码@Override
public void refresh() throws BeansException, IllegalStateException {
   synchronized (this.startupShutdownMonitor) {
      StartupStep contextRefresh = this.applicationStartup.start("spring.context.refresh");

      // Prepare this context for refreshing.
      prepareRefresh();

      // a.此处加载AnnotationAwareAspectJAutoProxyCreator的bean定义
      ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

      // Prepare the bean factory for use in this context.
      prepareBeanFactory(beanFactory);

      try {
         // Allows post-processing of the bean factory in context subclasses.
         postProcessBeanFactory(beanFactory);

         StartupStep beanPostProcess = this.applicationStartup.start("spring.context.beans.post-process");
         // Invoke factory processors registered as beans in the context.
         invokeBeanFactoryPostProcessors(beanFactory);

         // b.注册和创建AnnotationAwareAspectJAutoProxyCreator对象
         registerBeanPostProcessors(beanFactory);
         beanPostProcess.end();

         // Initialize message source for this context.
         initMessageSource();

         // Initialize event multicaster for this context.
         initApplicationEventMulticaster();

         // Initialize other special beans in specific context subclasses.
         onRefresh();

         // Check for listener beans and register them.
         registerListeners();

         // c.注册创建普通的bean对象
         finishBeanFactoryInitialization(beanFactory);

         // Last step: publish corresponding event.
         finishRefresh();
      }

scss复制代码@Override
protected final void refreshBeanFactory() throws BeansException {
   if (hasBeanFactory()) {
      destroyBeans();
      closeBeanFactory();
   }
   try {
      DefaultListableBeanFactory beanFactory = createBeanFactory();
      beanFactory.setSerializationId(getId());
      //对IOC容器进行定制化,如设置是否允许循环引用、是否允许bean定义覆盖重写等
      customizeBeanFactory(beanFactory);
      //加载Bean定义
      loadBeanDefinitions(beanFactory);
      this.beanFactory = beanFactory;
   }
   catch (IOException ex) {
      throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
   }
}

scss复制代码public static void registerBeanPostProcessors(
      ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) {
      //查找实现了BeanPostProcessor的类
   String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false);

   int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length;
   beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));

   // Separate between BeanPostProcessors that implement PriorityOrdered,
   // Ordered, and the rest.
   // 存放实现PriorityOrdered的PostProcessors
   List<BeanPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
   // 存放实现MergedBeanDefinitionPostProcessor的PostProcessors
   List<BeanPostProcessor> internalPostProcessors = new ArrayList<>();
   // 存放实现Ordered的PostProcessors
   List<String> orderedPostProcessorNames = new ArrayList<>();
   // 存放以外情况的PostProcessors
   List<String> nonOrderedPostProcessorNames = new ArrayList<>();
   for (String ppName : postProcessorNames) {
      if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
         BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
         // 此时PostProcessors对象还没有被创建,所以存放beanName
         priorityOrderedPostProcessors.add(pp);
         if (pp instanceof MergedBeanDefinitionPostProcessor) {
            internalPostProcessors.add(pp);
         }
      }
      else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
         orderedPostProcessorNames.add(ppName);
      }
      else {
         nonOrderedPostProcessorNames.add(ppName);
      }
   }

   // First, register the BeanPostProcessors that implement PriorityOrdered.
   sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
   registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);

   // Next, register the BeanPostProcessors that implement Ordered.
   // 这里注册实现了Ordered的BeanPostProcessors
   List<BeanPostProcessor> orderedPostProcessors = new ArrayList<>(orderedPostProcessorNames.size());
   for (String ppName : orderedPostProcessorNames) {
       // 重点:创建BeanPostProcessors对象 最终会调用执行doCreateBean方法.
      BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
      orderedPostProcessors.add(pp);
      if (pp instanceof MergedBeanDefinitionPostProcessor) {
         internalPostProcessors.add(pp);
      }
   }
   sortPostProcessors(orderedPostProcessors, beanFactory);
   //将创建好的BeanPostProcessors对象 存放到beanPostProcessors列表中.
   registerBeanPostProcessors(beanFactory, orderedPostProcessors);

   // Now, register all regular BeanPostProcessors.
   List<BeanPostProcessor> nonOrderedPostProcessors = new ArrayList<>(nonOrderedPostProcessorNames.size());
   for (String ppName : nonOrderedPostProcessorNames) {
      BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
      nonOrderedPostProcessors.add(pp);
      if (pp instanceof MergedBeanDefinitionPostProcessor) {
         internalPostProcessors.add(pp);
      }
   }
   registerBeanPostProcessors(beanFactory, nonOrderedPostProcessors);

   // Finally, re-register all internal BeanPostProcessors.
   sortPostProcessors(internalPostProcessors, beanFactory);
   registerBeanPostProcessors(beanFactory, internalPostProcessors);

   // Re-register post-processor for detecting inner beans as ApplicationListeners,
   // moving it to the end of the processor chain (for picking up proxies etc).
   beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext));
}

scss复制代码//省略。。。。
if (instanceWrapper == null) {
    // 创建对象
    instanceWrapper = createBeanInstance(beanName, mbd, args);
}
//省略。。。。
// Initialize the bean instance.
Object exposedObject = bean;
try {
    // 填充Bean，设置属性啥的
   populateBean(beanName, mbd, instanceWrapper);
   // 初始化Bean
   exposedObject = initializeBean(beanName, exposedObject, mbd);
}
//省略。。。。

ini复制代码protected Object initializeBean(String beanName, Object bean, @Nullable RootBeanDefinition mbd) {
   if (System.getSecurityManager() != null) {
      AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
         invokeAwareMethods(beanName, bean);
         return null;
      }, getAccessControlContext());
   }
   else {
      invokeAwareMethods(beanName, bean);
   }

   Object wrappedBean = bean;
   if (mbd == null || !mbd.isSynthetic()) {
       // 1. 执行每一个 BeanPostProcessor 的 postProcessBeforeInitialization 方法   
      wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
   }

   try {
       // 调用 bean 配置中的 init-method="xxx"
      invokeInitMethods(beanName, wrappedBean, mbd);
   }
   ....
   if (mbd == null || !mbd.isSynthetic()) {
       // 2.重点关注 执行每一个 BeanPostProcessor 的 postProcessAfterInitialization方法
      wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
   }

   return wrappedBean;
}

less复制代码@Override
public Object postProcessAfterInitialization(@Nullable Object bean, String beanName) {
    //此处的参数bean和beanName就是目标对象,此时目标对象已经被创建出来了.
   if (bean != null) {
       //从缓存中获取bean的名字key,如果是FactoryBean类型的key前面加&标识，以外的正常返回
      Object cacheKey = getCacheKey(bean.getClass(), beanName);
      if (this.earlyProxyReferences.remove(cacheKey) != bean) {
          //执行处理,处理完如果是aop类型就返回代理后的对象，给到ioc容器
         return wrapIfNecessary(bean, beanName, cacheKey);
      }
   }
   return bean;
}

kotlin复制代码protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) {
   //beanName不可空 && 已经处理过的直接返回
   if (StringUtils.hasLength(beanName) && this.targetSourcedBeans.contains(beanName)) {
      return bean;
   }
   //advisedBeans中包含是类型为Advice、Pointcut、Advisor、AopInfrastructureBean都跳过直接返回.
   if (Boolean.FALSE.equals(this.advisedBeans.get(cacheKey))) {
      return bean;
   }
   //同样的处理
   if (isInfrastructureClass(bean.getClass()) || shouldSkip(bean.getClass(), beanName)) {
      this.advisedBeans.put(cacheKey, Boolean.FALSE);
      return bean;
   }
   // 4.5.1 寻找匹配该目标Bean的横切逻辑方法(advice和advisor之类的)
   // 在我们上面的例子就是UserAdvice里的before和afterReturning方法
   Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null);
   if (specificInterceptors != DO_NOT_PROXY) {
      this.advisedBeans.put(cacheKey, Boolean.TRUE);
      //4.5.2生成真正的代理对象proxy，即利用JDK动态代理或cglib生成的$proxy0@xxx对象
      Object proxy = createProxy(
            bean.getClass(), beanName, specificInterceptors, new SingletonTargetSource(bean));
      this.proxyTypes.put(cacheKey, proxy.getClass());
      return proxy;
   }

   this.advisedBeans.put(cacheKey, Boolean.FALSE);
   return bean;
}

less复制代码@Nullable
protected abstract Object[] getAdvicesAndAdvisorsForBean(Class<?> beanClass, String beanName,
      @Nullable TargetSource customTargetSource) throws BeansException;

less复制代码protected Object[] getAdvicesAndAdvisorsForBean(
      Class<?> beanClass, String beanName, @Nullable TargetSource targetSource) {
   //查找合适的advisor(继承和注解advisor的类)
   List<Advisor> advisors = findEligibleAdvisors(beanClass, beanName);
   if (advisors.isEmpty()) {
      return DO_NOT_PROXY;
   }
   return advisors.toArray();
}

scss复制代码protected List<Advisor> findEligibleAdvisors(Class<?> beanClass, String beanName) {
   //先找到容器中全部的advisor
   List<Advisor> candidateAdvisors = findCandidateAdvisors();
   //再匹配beanName对应的advisor
   List<Advisor> eligibleAdvisors = findAdvisorsThatCanApply(candidateAdvisors, beanClass, beanName);
   extendAdvisors(eligibleAdvisors);
   if (!eligibleAdvisors.isEmpty()) {
      eligibleAdvisors = sortAdvisors(eligibleAdvisors);
   }
   return eligibleAdvisors;
}

kotlin复制代码protected List<Advisor> findCandidateAdvisors() {
   // 找到所有继承了Advisor.class的子类
   List<Advisor> advisors = super.findCandidateAdvisors();
   // Build Advisors for all AspectJ aspects in the bean factory.
   if (this.aspectJAdvisorsBuilder != null) {
       //寻找注解的advisor
      advisors.addAll(this.aspectJAdvisorsBuilder.buildAspectJAdvisors());
   }
   return advisors;
}

scss复制代码public static List<Advisor> findAdvisorsThatCanApply(List<Advisor> candidateAdvisors, Class<?> clazz) {
   if (candidateAdvisors.isEmpty()) {
      return candidateAdvisors;
   }
   List<Advisor> eligibleAdvisors = new ArrayList<>();
   for (Advisor candidate : candidateAdvisors) {
      if (candidate instanceof IntroductionAdvisor && canApply(candidate, clazz)) {
         eligibleAdvisors.add(candidate);
      }
   }
   boolean hasIntroductions = !eligibleAdvisors.isEmpty();
   for (Advisor candidate : candidateAdvisors) {
      if (candidate instanceof IntroductionAdvisor) {
         // already processed
         continue;
      }
      if (canApply(candidate, clazz, hasIntroductions)) {
         eligibleAdvisors.add(candidate);
      }
   }
   return eligibleAdvisors;
}

scss复制代码protected Object createProxy(Class<?> beanClass, @Nullable String beanName,
      @Nullable Object[] specificInterceptors, TargetSource targetSource) {

   if (this.beanFactory instanceof ConfigurableListableBeanFactory) {
      AutoProxyUtils.exposeTargetClass((ConfigurableListableBeanFactory) this.beanFactory, beanName, beanClass);
   }

   ProxyFactory proxyFactory = new ProxyFactory();
   proxyFactory.copyFrom(this);
   // 判断proxy-target-class="true"
   if (proxyFactory.isProxyTargetClass()) {
      if (Proxy.isProxyClass(beanClass)) {
         for (Class<?> ifc : beanClass.getInterfaces()) {
            proxyFactory.addInterface(ifc);
         }
      }
   }
   else {
      // No proxyTargetClass flag enforced, let's apply our default checks...
      if (shouldProxyTargetClass(beanClass, beanName)) {
         proxyFactory.setProxyTargetClass(true);
      }
      else {
         evaluateProxyInterfaces(beanClass, proxyFactory);
      }
   }

   Advisor[] advisors = buildAdvisors(beanName, specificInterceptors);
   proxyFactory.addAdvisors(advisors);
   proxyFactory.setTargetSource(targetSource);
   customizeProxyFactory(proxyFactory);

   proxyFactory.setFrozen(this.freezeProxy);
   if (advisorsPreFiltered()) {
      proxyFactory.setPreFiltered(true);
   }

   // Use original ClassLoader if bean class not locally loaded in overriding class loader
   ClassLoader classLoader = getProxyClassLoader();
   if (classLoader instanceof SmartClassLoader && classLoader != beanClass.getClassLoader()) {
      classLoader = ((SmartClassLoader) classLoader).getOriginalClassLoader();
   }
   return proxyFactory.getProxy(classLoader);
}

less复制代码public Object getProxy(@Nullable ClassLoader classLoader) {
   return createAopProxy().getProxy(classLoader);
}

kotlin复制代码protected final synchronized AopProxy createAopProxy() {
   if (!this.active) {
      activate();
   }
   return getAopProxyFactory().createAopProxy(this);
}

arduino复制代码@Override
public AopProxy createAopProxy(AdvisedSupport config) throws AopConfigException {
   //此处的config参数就是proxyFactory对象
   if (!NativeDetector.inNativeImage() &&
         (config.isOptimize() || config.isProxyTargetClass() || hasNoUserSuppliedProxyInterfaces(config))) {
      Class<?> targetClass = config.getTargetClass();
       ... 
      if (targetClass.isInterface() || Proxy.isProxyClass(targetClass)) {
         return new JdkDynamicAopProxy(config);
      }
      return new ObjenesisCglibAopProxy(config);
   }
   else {
      return new JdkDynamicAopProxy(config);
   }
}

arduino复制代码public JdkDynamicAopProxy(AdvisedSupport config) throws AopConfigException {
   //如果不存在Advisor或者目标对象为空的话 抛出异常
   if (config.getAdvisorCount() == 0 && config.getTargetSource() == AdvisedSupport.EMPTY_TARGET_SOURCE) {
      throw new AopConfigException("No advisors and no TargetSource specified");
   }
   this.advised = config;
   //获取advised里代理对象所继承的所有接口
   this.proxiedInterfaces = AopProxyUtils.completeProxiedInterfaces(this.advised, true);
   //判断标记继承的接口是否有实现equals和hashCode方法
   findDefinedEqualsAndHashCodeMethods(this.proxiedInterfaces);
}

less复制代码@Override
public Object getProxy(@Nullable ClassLoader classLoader) {
   if (logger.isTraceEnabled()) {
      logger.trace("Creating JDK dynamic proxy: " + this.advised.getTargetSource());
   }
   return Proxy.newProxyInstance(classLoader, this.proxiedInterfaces, this);
}

kotlin复制代码final class JdkDynamicAopProxy implements AopProxy, InvocationHandler, Serializable {

kotlin复制代码public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
   Object oldProxy = null;
   boolean setProxyContext = false;

   TargetSource targetSource = this.advised.targetSource;
   Object target = null;

   try {
      if (!this.equalsDefined && AopUtils.isEqualsMethod(method)) {
         // The target does not implement the equals(Object) method itself.
         return equals(args[0]);
      }
      else if (!this.hashCodeDefined && AopUtils.isHashCodeMethod(method)) {
         // The target does not implement the hashCode() method itself.
         return hashCode();
      }
      //method.getDeclaringClass获取Method对应的目标类,method.getClass获得是Method类
      else if (method.getDeclaringClass() == DecoratingProxy.class) {
         // There is only getDecoratedClass() declared -> dispatch to proxy config.
         return AopProxyUtils.ultimateTargetClass(this.advised);
      }
      //Advised接口或者其父接口中定义的方法,直接反射调用,不应用通知
      else if (!this.advised.opaque && method.getDeclaringClass().isInterface() &&
            method.getDeclaringClass().isAssignableFrom(Advised.class)) {
         // Service invocations on ProxyConfig with the proxy config...
         return AopUtils.invokeJoinpointUsingReflection(this.advised, method, args);
      }

      Object retVal;

      if (this.advised.exposeProxy) {
         // Make invocation available if necessary.
         oldProxy = AopContext.setCurrentProxy(proxy);
         setProxyContext = true;
      }
      //获取目标对象的类
      target = targetSource.getTarget();
      Class<?> targetClass = (target != null ? target.getClass() : null);

      // 获取目标方法的拦截器链.程序上我们可以定义多个Aop切面,而某个目标方法就有可能被多个Aop匹配上，故需要循环执行每个匹配的aop通知.
      List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass);
      //拦截器链为空的，则直接调用目标对象方法
      if (chain.isEmpty()) { 
         Object[] argsToUse = AopProxyUtils.adaptArgumentsIfNecessary(method, args);
         retVal = AopUtils.invokeJoinpointUsingReflection(target, method, argsToUse);
      }
      else {
         // 创建MethodInvocation
         MethodInvocation invocation =
               new ReflectiveMethodInvocation(proxy, target, method, args, targetClass, chain);
         // Proceed to the joinpoint through the interceptor chain.
         retVal = invocation.proceed();
      }

      //最终方法执行的返回结果
      Class<?> returnType = method.getReturnType();
      if (retVal != null && retVal == target &&
            returnType != Object.class && returnType.isInstance(proxy) &&
            !RawTargetAccess.class.isAssignableFrom(method.getDeclaringClass())) {
         retVal = proxy;
      }
      else if (retVal == null && returnType != Void.TYPE && returnType.isPrimitive()) {
         throw new AopInvocationException(
               "Null return value from advice does not match primitive return type for: " + method);
      }
      return retVal;
   }
   finally {
      if (target != null && !targetSource.isStatic()) {
         // Must have come from TargetSource.
         targetSource.releaseTarget(target);
      }
      if (setProxyContext) {
         // Restore old proxy.
         AopContext.setCurrentProxy(oldProxy);
      }
   }
}

kotlin复制代码public Object proceed() throws Throwable {
   // 如果执行Interceptor完了，则执行joinPoint.注意currentInterceptorIndex初始值为-1
   if (this.currentInterceptorIndex == this.interceptorsAndDynamicMethodMatchers.size() - 1) {
      return invokeJoinpoint();
   }
   // 执行Interceptor,根据currentInterceptorIndex逐个获取Interceptor
   Object interceptorOrInterceptionAdvice =
         this.interceptorsAndDynamicMethodMatchers.get(++this.currentInterceptorIndex);
   //是否需要动态匹配     
   if (interceptorOrInterceptionAdvice instanceof InterceptorAndDynamicMethodMatcher) {
      // Evaluate dynamic method matcher here: static part will already have
      // been evaluated and found to match.
      InterceptorAndDynamicMethodMatcher dm =
            (InterceptorAndDynamicMethodMatcher) interceptorOrInterceptionAdvice;
      Class<?> targetClass = (this.targetClass != null ? this.targetClass : this.method.getDeclaringClass());
      if (dm.methodMatcher.matches(this.method, targetClass, this.arguments)) {
         return dm.interceptor.invoke(this);
      }
      else {
         // Dynamic matching failed.
         // Skip this interceptor and invoke the next in the chain.
         return proceed();
      }
   }
   else {
      // It's an interceptor, so we just invoke it: The pointcut will have
      // been evaluated statically before this object was constructed.
      //执行当前IntercetporAdvice的invoke方法
      return ((MethodInterceptor) interceptorOrInterceptionAdvice).invoke(this);
   }
}

scss复制代码public Object invoke(MethodInvocation mi) throws Throwable {
   //先执行before方法,执行完后再回调ReflectiveMethodInvocation.proceed()
   this.advice.before(mi.getMethod(), mi.getArguments(), mi.getThis());
   return mi.proceed();
}

java复制代码public Object invoke(MethodInvocation mi) throws Throwable {
    //先回调ReflectiveMethodInvocation.proceed(),因为调用joinPoint在这里
   Object retVal = mi.proceed();
   //再执行afterReturning
   this.advice.afterReturning(retVal, mi.getMethod(), mi.getArguments(), mi.getThis());
   return retVal;
}

scss复制代码Input
["CombinationIterator", "next", "hasNext", "next", "hasNext", "next", "hasNext"]
[["abc", 2], [], [], [], [], [], []]
Output
[null, "ab", true, "ac", true, "bc", false]

Explanation
CombinationIterator itr = new CombinationIterator("abc", 2);
itr.next();    // return "ab"
itr.hasNext(); // return True
itr.next();    // return "ac"
itr.hasNext(); // return True
itr.next();    // return "bc"
itr.hasNext(); // return False

vbnet复制代码1 <= combinationLength <= characters.length <= 15
All the characters of characters are unique.
At most 10^4 calls will be made to next and hasNext.
It's guaranteed that all calls of the function next are valid.

python复制代码class CombinationIterator(object):

    def __init__(self, characters, combinationLength):
        """
        :type characters: str
        :type combinationLength: int
        """
        self.characters = characters
        self.L = [''.join(i) for i in itertools.combinations(characters, combinationLength)]
        

    def next(self):
        """
        :rtype: str
        """
        return self.L.pop(0)
        
        
    def hasNext(self):
        """
        :rtype: bool
        """
        if self.L:
            return True
        return False

rust复制代码Runtime: 44 ms, faster than 81.82% of Python online submissions for Iterator for Combination.
Memory Usage: 16 MB, less than 72.73% of Python online submissions for Iterator for Combination.

python复制代码class CombinationIterator(object):

    def __init__(self, characters, combinationLength):
        """
        :type characters: str
        :type combinationLength: int
        """
        self.characters = characters
        self.n = combinationLength
        self.N = len(characters)
        self.L = []
        self.permute('', 0)
    
    def permute(self, s, start):
        if len(s) == self.n:
            self.L.append(s)
            return
        else:
            for i in range(start, self.N):
                self.permute(s + self.characters[i], i + 1)

    def next(self):
        """
        :rtype: str
        """
        return self.L.pop(0)
        
        
    def hasNext(self):
        """
        :rtype: bool
        """
        if self.L:
            return True
        return False

rust复制代码Runtime: 52 ms, faster than 54.55% of Python online submissions for Iterator for Combination.
Memory Usage: 15.9 MB, less than 72.73% of Python online submissions for Iterator for Combination.