kotlin复制代码abstract suspend fun load(loadType: LoadType, state: PagingState<Key, Value>): MediatorResult

less复制代码sealed class MediatorResult {
    class Error(val throwable: Throwable) : MediatorResult()

    class Success(
        @get:JvmName("endOfPaginationReached") val endOfPaginationReached: Boolean
    ) : MediatorResult()
}

kotlin复制代码sealed class LoadState( val endOfPaginationReached: Boolean) {
    class NotLoading( endOfPaginationReached: Boolean) :LoadState(endOfPaginationReached) {
        ......
    }

    object Loading : LoadState(false) {
        ......
    }

    class Error(val error: Throwable) : LoadState(false) {
        ......
    }
}

csharp复制代码sealed class PokemonResult<out T> {
    data class Success<out T>(val value: T) : PokemonResult<T>()

    data class Failure(val throwable: Throwable?) : PokemonResult<Nothing>()
}

kotlin复制代码override suspend fun featchPokemonInfo(name: String): Flow<PokemonResult<PokemonInfoModel>> {
    return flow {
        try {
            
            emit(PokemonResult.Success(model)) // 成功
        } catch (e: Exception) {
            emit(PokemonResult.Failure(e.cause)) // 失败
        }
    }.flowOn(Dispatchers.IO) // 通过 flowOn 切换到 io 线程
}

csharp复制代码when (result) {
    is PokemonResult.Failure -> {
        _failure.value = result.throwable?.message ?: "failure"
    }
    is PokemonResult.Success -> {
        _pokemon.postValue(result.value)
    }
}

kotlin复制代码inline fun <reified T> PokemonResult<T>.doSuccess(success: (T) -> Unit) {
    if (this is PokemonResult.Success) {
        success(value)
    }
}

inline fun <reified T> PokemonResult<T>.doFailure(failure: (Throwable?) -> Unit) {
    if (this is PokemonResult.Failure) {
        failure(throwable)
    }
}

scss复制代码result.doFailure { throwable ->
    _failure.value = throwable?.message ?: "failure"
}
result.doSuccess { value ->
    _pokemon.postValue(value)
    emit(value)
}

css复制代码android {
    kotlinOptions {
        freeCompilerArgs += ["-Xopt-in=kotlin.RequiresOptIn"]
    }
}

kotlin复制代码@Dao
interface PokemonDao {

    @Insert(onConflict = OnConflictStrategy.REPLACE)
    suspend fun insertPokemon(pokemonList: List<PokemonEntity>)

    @Query("SELECT * FROM PokemonEntity")
    fun getPokemon(): PagingSource<Int, PokemonEntity>

}

kotlin复制代码@OptIn(ExperimentalPagingApi::class)
class PokemonRemoteMediator(
    val api: PokemonService,
    val db: AppDataBase
) : RemoteMediator<Int, PokemonEntity>() {

    override suspend fun load(
        loadType: LoadType,
        state: PagingState<Int, PokemonEntity>
    ): MediatorResult {
       /**
         * 在这个方法内将会做三件事
         *
         * 1. 参数 LoadType 有个三个值，关于这三个值如何进行判断
         *      LoadType.REFRESH
         *      LoadType.PREPEND
         *      LoadType.APPEND
         *
         * 2. 请问网络数据
         *
         * 3. 将网络数据插入到本地数据库中
         */
    }
}

kotlin复制代码val pageKey = when (loadType) {
   // 首次访问 或者调用 PagingDataAdapter.refresh()
   LoadType.REFRESH -> null
   // 在当前加载的数据集的开头加载数据时
   LoadType.PREPEND -> return MediatorResult.Success(endOfPaginationReached = true)
   LoadType.APPEND -> { // 下来加载更多时触发
       /**
        * 方式一：这种方式比较简单，当前页面最后一条数据是下一页的开始位置
        * 通过 load 方法的参数 state 获取当页面最后一条数据
        */
//       val lastItem = state.lastItemOrNull()
//       if (lastItem == null) {
//           return MediatorResult.Success(
//             endOfPaginationReached = true
//          )
//         }
//        lastItem.page

       /**
        * 方式二：比较麻烦，当前分页数据没有对应的远程 key，这个时候需要我们自己建表
        */
       val remoteKey = db.withTransaction {
           db.remoteKeysDao().getRemoteKeys(remotePokemon)
       }
       if (remoteKey == null || remoteKey.nextKey == null) {
           return MediatorResult.Success(endOfPaginationReached = true)
       }
       remoteKey.nextKey
   }
}

ini复制代码val page = pageKey ?: 0
val result = api.fetchPokemonList(
    state.config.pageSize,
    page * state.config.pageSize
).results

scss复制代码remoteKeysDao.insertAll(entity)
pokemonDao.insertPokemon(item)

scss复制代码Pager(
    config = pageConfig,
    remoteMediator = PokemonRemoteMediator(api, db)
) {
    db.pokemonDao().getPokemon()
}.flow.map { pagingData ->
    pagingData.map { mapper2ItemMolde.map(it) }
}

kotlin复制代码fun postOfData(): LiveData<PagingData<PokemonItemModel>> =
    polemonRepository.featchPokemonList().cachedIn(viewModelScope).asLiveData()

kotlin复制代码fun <T : Any> Flow<PagingData<T>>.cachedIn(
    scope: CoroutineScope
)

java复制代码public static <T> List<T> unmodifiableList(List<? extends T> list) {  
    return (list instanceof RandomAccess ?  
            new Collections.UnmodifiableRandomAccessList<>(list) :  
            new Collections.UnmodifiableList<>(list));  
}

java复制代码List<String> list = new ArrayList<>(Arrays.asList("沉默王二", "沉默王三", "沉默王四"));  
List<String> unmodifiableList = Collections.unmodifiableList(list);

java复制代码unmodifiableList.add("沉默王五");

复制代码Exception in thread "main" java.lang.UnsupportedOperationException  
    at java.base/java.util.Collections$UnmodifiableCollection.add(Collections.java:1062)  
    at com.cmower.mkyong.immutablelist.ImmutableListDemo.main(ImmutableListDemo.java:16)

java复制代码static <E> List<E> of(E e1, E e2, E e3) {  
    return new ImmutableCollections.ListN<>(e1, e2, e3);  
}

java复制代码static <E> List<E> of(E e1) {  
        return new ImmutableCollections.List12<>(e1);  
    }  
static <E> List<E> of(E e1, E e2) {  
        return new ImmutableCollections.List12<>(e1, e2);  
    }  
static <E> List<E> of(E e1, E e2, E e3, E e4) {  
    return new ImmutableCollections.ListN<>(e1, e2, e3, e4);  
}  
static <E> List<E> of(E e1, E e2, E e3, E e4, E e5) {  
    return new ImmutableCollections.ListN<>(e1, e2, e3, e4, e5);  
}  
static <E> List<E> of(E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8, E e9, E e10) {  
    return new ImmutableCollections.ListN<>(e1, e2, e3, e4, e5,  
            e6, e7, e8, e9, e10);  
}

java复制代码static <E> List<E> of(E... elements) {  
    switch (elements.length) { // implicit null check of elements  
        case 0:  
            @SuppressWarnings("unchecked")  
            var list = (List<E>) ImmutableCollections.ListN.EMPTY_LIST;  
            return list;  
        case 1:  
            return new ImmutableCollections.List12<>(elements[0]);  
        case 2:  
            return new ImmutableCollections.List12<>(elements[0], elements[1]);  
        default:  
            return new ImmutableCollections.ListN<>(elements);  
    }  
}

java复制代码static final class List12<E> extends ImmutableCollections.AbstractImmutableList<E>  
        implements Serializable {  
  
    @Stable  
    private final E e0;  
  
    @Stable  
    private final E e1;  
}  
  
static final class ListN<E> extends ImmutableCollections.AbstractImmutableList<E>  
        implements Serializable {  
  
    // EMPTY_LIST may be initialized from the CDS archive.  
    static @Stable List<?> EMPTY_LIST;  
  
    static {  
        VM.initializeFromArchive(ImmutableCollections.ListN.class);  
        if (EMPTY_LIST == null) {  
            EMPTY_LIST = new ImmutableCollections.ListN<>();  
        }  
    }  
  
    @Stable  
    private final E[] elements;  
}

java复制代码final List<String> unmodifiableList = List.of("沉默王二", "沉默王三", "沉默王四");  
unmodifiableList.add("沉默王五");

复制代码Exception in thread "main" java.lang.UnsupportedOperationException  
    at java.base/java.util.ImmutableCollections.uoe(ImmutableCollections.java:73)  
    at java.base/java.util.ImmutableCollections$AbstractImmutableCollection.add(ImmutableCollections.java:77)  
    at com.cmower.mkyong.immutablelist.ImmutableListDemo.main(ImmutableListDemo.java:20)

复制代码<dependency>  
    <groupId>com.google.guava</groupId>  
    <artifactId>guava</artifactId>  
    <version>28.1-jre</version>  
</dependency>

java复制代码@GwtCompatible(serializable = true, emulated = true)  
@SuppressWarnings("serial") // we're overriding default serialization  
public abstract class ImmutableList<E> extends ImmutableCollection<E>  
    implements List<E>, RandomAccess {  
}

java复制代码java.lang.Object  
  ↳ java.util.AbstractCollection  
      ↳ com.google.common.collect.ImmutableCollection  
          ↳ com.google.common.collect.ImmutableList

java复制代码List<String> list = new ArrayList<>(Arrays.asList("沉默王二", "沉默王三", "沉默王四"));  
List<String> unmodifiableList = ImmutableList.copyOf(list);  
unmodifiableList.add("沉默王五");

复制代码Exception in thread "main" java.lang.UnsupportedOperationException  
    at com.google.common.collect.ImmutableCollection.add(ImmutableCollection.java:244)  
    at com.cmower.mkyong.immutablelist.ImmutableListDemo.main(ImmutableListDemo.java:25)

java复制代码List<String> unmodifiableList = ImmutableList.of("沉默王二", "沉默王三", "沉默王四");

java复制代码ImmutableList<String> iList = ImmutableList.<String>builder()  
        .add("沉默王二", "沉默王三", "沉默王四")  
        .build();  
  
List<String> list = List.of("沉默王二", "沉默王三", "沉默王四");  
ImmutableList<String> iList = ImmutableList.<String>builder()  
        .addAll(list)  
        .build();  
  
List<String> list = List.of("沉默王二", "沉默王三", "沉默王四");  
ImmutableList<String> iList = ImmutableList.<String>builder()  
        .addAll(list)  
        .add("沉默王五")  
        .build();

java复制代码List<String> list = new ArrayList<>();  
list.add("沉默王二");  
  
List<String> iList = Collections.unmodifiableList(list);  
  
list.add("沉默王三");  
list.add("沉默王四");  
  
System.out.println(iList);

复制代码[沉默王二, 沉默王三, 沉默王四]

java复制代码List<String> list = new ArrayList<>();  
list.add("沉默王二");  
  
ImmutableList<String> iList = ImmutableList.copyOf(list);  
  
list.add("沉默王三");  
list.add("沉默王四");  
  
System.out.println(iList);

复制代码[沉默王二]

复制代码    /**
     * Returns a power of two size for the given target capacity.
     */
    static final int tableSizeFor(int cap) {
        int n = cap - 1;
        n |= n >>> 1;
        n |= n >>> 2;
        n |= n >>> 4;
        n |= n >>> 8;
        n |= n >>> 16;
        return (n < 0) ? 1 : (n >= MAXIMUM_CAPACITY) ? MAXIMUM_CAPACITY : n + 1;
    }

复制代码    public V put(K key, V value) {
        return putVal(hash(key), key, value, false, true);
    }
    
    static final int hash(Object key) {
        int h;
        return (key == null) ? 0 : (h = key.hashCode()) ^ (h >>> 16);
    }
    
    final V putVal(int hash, K key, V value, boolean onlyIfAbsent,
                   boolean evict) {
        ...
        if ((p = tab[i = (n - 1) & hash]) == null)
            tab[i] = newNode(hash, key, value, null);
        ...
    }

复制代码import pandas as pd
import numpy as np
import os
import seaborn as sns
import matplotlib.pyplot as plt
# 绘图显示中文
plt.rcParams['font.sans-serif'] = ['SimHei']
plt.rcParams['axes.unicode_minus'] = False

复制代码file_list = os.listdir('./data/a-share/')

pieces = []
for file_name in file_list:
    path = './data/a-share/%s' % file_name
    file = pd.read_csv(path, encoding ='gb2312')
    pieces.append(file)
    
shares = pd.concat(pieces)

复制代码shares.reset_index(inplace=True, drop=True)
shares.head()

复制代码len(shares['代码'].unique())

复制代码# 计算每只股票的最早交易时间（即：上市时间）
shares_min_date = shares.groupby('简称').agg({'日期':'min'})
shares_min_date['上市年份'] = shares_min_date['日期'].apply(lambda x: str(x)[:4])

# 每年上市公司的数量
shares_min_date.groupby('上市年份').count().plot()

复制代码shares_market_value = shares[shares['日期'] == '2016-06-08'][['简称', '总市值(元)']].sort_values(by='总市值(元)', ascending=False)

# 市值最大的公司 top10
tmp_df = shares_market_value.head(10)

# 画图
sns.barplot(x=tmp_df['总市值(元)'], y=tmp_df['简称'])

复制代码shares_110609 = shares[shares['日期'] == '2011-06-09'][['代码', '简称', '收盘价(元)']]
shares_160609 = shares[shares['日期'] == '2016-06-08'][['代码', '收盘价(元)']]

# 按照股票代码将2天数据关联
shares_price = shares_110609.merge(shares_160609, on='代码')
shares_price

复制代码# 多少家股票是上涨的
shares_price[shares_price['涨跌幅(%)'] > 0].count()

复制代码# 多少家股票是上涨的
shares_price[shares_price['涨跌幅(%)'] < 0].count()

复制代码bins = np.array([0, 40, 70, 100, 1700])
# 股价上涨的公司
shares_up = shares_price[shares_price['涨跌幅(%)'] > 0]
# 按涨幅进行分组
shares_up['label'] = pd.cut(shares_up['涨跌幅(%)'], bins)
# 分组统计
up_label_count = shares_up[['label', '代码']].groupby('label').count()
up_label_count['占比'] = up_label_count['代码'] / up_label_count.sum().values
sns.barplot(x=up_label_count['占比'], y=up_label_count.index)

复制代码# 涨幅最大的公司
tmp_df = shares_up.sort_values(by='涨跌幅(%)', ascending=False)[:8]
sns.barplot(y=tmp_df['简称'], x=tmp_df['涨跌幅(%)'])

复制代码// of 方法是 Java9 开始提供的静态工厂
java.util.List.of(1, 2, 3, 4, 5)
                .stream()
                .filter(i -> i > 3)
                .map(i -> i * 2)
                .collect(Collectors.toList());

复制代码io.vavr.collection.List.of(1, 2, 3, 4, 5)
    .filter(i -> i > 3)
    .map(i -> i * 2);

复制代码var list = io.vavr.collection.List.of(1, 2)
var list2 = list
  .append(List.of(3, 4))
  .append(List.of(5, 6))
  .append(7);
// list = [1, 2]
// list2 = [1, 2, 3, 4, 5, 6]

复制代码var javaList = java.util.List.of(1, 2, 3);
java.util.List<Integer> javaList2 = io.vavr.collection.List.ofAll(javaList)
    .filter(i -> i > 1)
    .map(i -> i * 2)
    .toJavaList();

复制代码/**
* 用户信息
*/
@Data
class User {
  private Long id;
  private String name;
  private Integer age;
}

复制代码public Map<Integer, List<String>> userStatistic(List<User> users) {
    return users.stream()
      .filter(u -> u.getAge() >= 18)
      .collect(Collectors.groupingBy(User::getAge, Collectors.mapping(User::getName, Collectors.toList())));
}

复制代码public Map<Integer, List<String>> userStatistic(List<User> users) {
    return users.filter(u -> u.getAge() >= 18)
      .groupBy(User::getAge)
      .mapValues(usersGroup -> usersGroup.map(User::getName));
}

复制代码// scala 的元组，用括号构建
val tup = (1, "ok", true)

// 按索引取值，执行对应类型的操作
val sum = tup._1 + 2  // int 加法
val world = "hello "+tup._2 // 字符串拼接
val res = !tup._3 // 布尔取反

复制代码import io.vavr.Tuple;

public TupleTest {
  
    @Test
    public void testTuple() {
        // 一元组
        var oneTuple = Tuple.of("string");
        String oneTuple_1 = oneTuple._1;

        // 二元组
        var twoTuple = Tuple.of("string", 1);
        String twoTuple_1 = twoTuple._1;
        Integer twoTuple_2 = twoTuple._2;

      	// 五元组
        var threeTuple = Tuple.of("string", 2, 1.2F, 2.4D, 'c');
        String threeTuple_1 = threeTuple._1;
        Integer threeTuple_2 = threeTuple._2;
        Float threeTuple_3 = threeTuple._3;
        Double threeTuple_4 = threeTuple._4;
        Character threeTuple_5 = threeTuple._5;
    }
}

复制代码Tuple5<String, Integer, Float, Double, Character> tuple5 = Tuple.of("string", 2, 1.2F, 2.4D, 'c');

复制代码var tup = Tuple.of("hello", 1);

// 模式匹配
Match(tup).of(
   Case($Tuple2($(is("hello")), $(is(1))), (t1, t2) -> run(() -> {})),
   Case($Tuple2($(), $()),(t1, t2) ->run(() -> {}))
);

复制代码// 等同于 if...else
if (tup._1.equalas("hello")  && tup._2 == 1) {
  // ...  do something
} else {
  // ... do something
}

复制代码@Test
public void testOption() {
  	// 通过 of 工厂方法构造
    Assert.assertTrue(Option.of(null) instanceof Option.None);
    Assert.assertTrue(Option.of(1) instanceof Option.Some);
    
  	// 通过 none 或 some 构造
    Assert.assertTrue(Option.none() instanceof Option.Some);
    Assert.assertTrue(Option.some(1) instanceof Option.Some);
}

复制代码@Test
public void testOptional() {
    Assert.assertTrue(Optional.ofNullable(null) instanceof Optional);
    Assert.assertTrue(Optional.of(1) instanceof Optional);
    Assert.assertTrue(Optional.empty() instanceof Optional);
    Assert.assertTrue(Optional.ofNullable(1) instanceof Optional);
}

复制代码@Test
public void testWithJavaOptional() {
    // Java Optional
    var result = Optional.of("hello")
      .map(str -> (String) null)
      .orElseGet(() -> "world");

  	// result = "world"
    Assert.assertEquals("word", result);
}

@Test
public void testWithVavrOption() {
  	// Vavr Option
    var result = Option.of("hello")
      .map(str -> (String) null)
      .getOrElse(() -> "world");
  
  	// result = null
    Assert.assertNull(result);
}

复制代码
@Test
public void testVavrOption() {
  	// option 直接转为 List
    List<String> result = Option.of("vavr hello world")
      .map(String::toUpperCase)
      .toJavaList();
    Assert.assertNotNull(result);
    Assert.assertEquals(1, result.size());
    Assert.assertEquals("vavr hello world", result.iterator().next());
  
  	// exists(Function)
    boolean exists = Option.of("ok").exists(str -> str.equals("ok"));
    Assert.assertTrue(exists);

  	// contains
    boolean contains = Option.of("ok").contains("ok");
    Assert.assertTrue(contains);
}

复制代码Option.of("toJava").toJavaOptional();

Option.ofOptional(Optional.empty());

复制代码try {
	//..
} catch (Throwable t) {
	//...
} finally {
  //....
}

复制代码/**
* 输出
*	 failure: / by zero
*  finally
*/
Try.of(() -> 1 / 0)
    .andThen(r -> System.out.println("and then " + r))
    .onFailure(error -> System.out.println("failure" + error.getMessage()))
    .andFinally(() -> {
      System.out.println("finally");
    });

复制代码@Test
public void testTryInstance() {
  	// 除以 0 ，构建出 Failure
    var error = Try.of(() -> 0 / 0);
    Assert.assertTrue(error instanceof Try.Failure);

  	// 合法的加法，构建出 Success
    var normal = Try.of(() -> 1 + 1);
    Assert.assertTrue(normal instanceof Try.Success);
}

复制代码@Test
public void testTryWithRecover() {
    Assert.assertEquals("NPE", testTryWithRecover(new NullPointerException()));
    Assert.assertEquals("IllegalState", testTryWithRecover(new IllegalStateException()));
    Assert.assertEquals("Unknown", testTryWithRecover(new RuntimeException()));
}

private String testTryWithRecover(Exception e) {
    return (String) Try.of(() -> {
      throw e;
    })
      .recoverWith(NullPointerException.class, Try.of(() -> "NPE"))
      .recoverWith(IllegalStateException.class, Try.of(() -> "IllegalState"))
      .recoverWith(RuntimeException.class, Try.of(() -> "Unknown"))
      .get();
}

复制代码@Test
public void testTryMap() {
    String res = Try.of(() -> "hello world")
      .map(String::toUpperCase)
      .toOption()
      .getOrElse(() -> "default");
    Assert.assertEquals("HELLO WORLD", res);
}

复制代码@Test
public void testFutureFailure() {
    final var word = "hello world";
    io.vavr.concurrent.Future
      .of(Executors.newFixedThreadPool(1), () -> word)
      .onFailure(throwable -> Assert.fail("不应该走到 failure 分支"))
      .onSuccess(result -> Assert.assertEquals(word, result));
}

@Test
public void testFutureSuccess() {
    io.vavr.concurrent.Future
      .of(Executors.newFixedThreadPool(1), () -> {
          throw new RuntimeException();
      })
      .onFailure(throwable -> Assert.assertTrue(throwable instanceof RuntimeException))
      .onSuccess(result -> Assert.fail("不应该走到 success 分支"));
}

复制代码Future.of(Executors.newFixedThreadPool(1), () -> "toJava").toCompletableFuture();

Future.fromCompletableFuture(CompletableFuture.runAsync(() -> {}));

复制代码public Either<Exception, String> compute() {
  //...
}

public void test() {
	Either<Exception, String> either = compute();
  
  // 异常值
  if (either.isLeft()) {
    Exception exception = compute().getLeft();
    throw new RuntimeException(exception);
  }

  // 正确值
  if (either.isRight()) {
    String result = compute().get();
    // ...
  }
}

复制代码Lazy<Double> lazy = Lazy.of(Math::random);
  lazy.isEvaluated(); // = false
  lazy.get();         // = 0.123 (random generated)
  lazy.isEvaluated(); // = true
  lazy.get();         // = 0.123 (memoized)

复制代码import static io.vavr.API.*;

@Test
public void testAPI() {
  // 构造 Option
  var some = Some(1);
  var none = None();

  // 构造 Future
  var future = Future(() -> "ok");

  // 构造 Try
  var tryInit = Try(() -> "ok");
}

复制代码def testPatternMatch(nameOpt: Option[String], nums: List[Int]) = {
	/**
	* 匹配 Option 的结构
	*/
  nameOpt match {
    case Some(name) => println(s"你好，$name")
    case None => println("无名之辈")
  }

  /**
  * 匹配 List 的结构
  */
  nums match {
    case Nil => println("空列表")
    case List(v) => println(s"size=1 $v")
    case List(v, v2) => println(s"size=2 $v、 $v2")
    case _ => println("size > 2")
  }
}

复制代码public String bmiFormat(double height, double weight) {
  double bmi = weight / (height * height);
  String desc;
  if (bmi < 18.5) {
    desc = "有些许晃荡！";
  } else if (bmi < 25) {
    desc = "继续加油哦！";
  } else if (bmi < 30) {
    desc = "你是真的稳！";
  } else {
    desc = "难受！";
  }
  return desc;
}

复制代码import static io.vavr.API.*;

复制代码public String bmiFormat(double height, double weight) {
  double bmi = weight / (height * height);
  return Match(bmi).of(
    // else if (bmi < 18.5)
    Case($(v -> v < 18.5), () -> "有些许晃荡！"),
    // else if (bmi < 25)
    Case($(v -> v < 25), () -> "继续加油哦！"),
    // else if (bmi < 30)
    Case($(v -> v < 30), () -> "你是真的稳！"),
    // else
    Case($(), () -> "难受！")
  );

}

复制代码public static <T> Match<T> Match(T value) {...}

public static <T, R> Case<T, R> Case(Pattern0<T> pattern, Function<? super T, ? extends R> f) {...}

public static <T> Pattern0<T> $(Predicate<? super T> predicate) {...}

复制代码public final <R> R of(Case<? extends T, ? extends R>... cases) {...}

复制代码匹配一下（这个东西）的结构，是不是下面的情况之一
// Match(XXX).Of(

  - 结构和 A 一样，做点什么事情
  //Case(  $(A),   () -> doSomethingA()   ),
  
  - 结构和 B 一样，做点什么事情
  //Case(  $(B),   () -> doSomethingB()   ),
  - .....
  
  - 和上面的结构都不一样，也做点事情
  //Case(  $(),    () -> doSomethingOthers())
  //);

复制代码import static io.vavr.API.*;
import static io.vavr.Patterns.$None;
import static io.vavr.Patterns.$Some;

public class PatternMatchTest {
  
    @Test
    public void testMatchNone() {
      // 匹配 None
        var noneOpt = Option.none();
        Match(noneOpt).of(
                Case($None(), r -> {
                    Assert.assertEquals(Option.none(), r);
                    return true;
                }),
                Case($(), this::failed)
        );
    }

    @Test
    public void testMatchValue() {
      // 匹配某一个值为 Nice 的 Some
        var opt2 = Option.of("Nice");
        Match(opt2).of(
                Case($Some($("Nice")), r -> {
                    Assert.assertEquals("Nice", r);
                    return true;
                }),
                Case($(), this::failed)
        );
    }

    @Test
    public void testMatchAnySome() {
      // 匹配 Some，值任意
        var opt = Option.of("hello world");
        Match(opt).of(
                Case($None(), this::failed),
                Case($Some($()), r -> {
                    Assert.assertEquals("hello world", r);
                    return true;
                })
        );
    }

    private boolean failed() {
        Assert.fail("不应该执行该分支");
        return false;
    }
}

复制代码import static io.vavr.API.*;
import static io.vavr.Patterns.*;
import static io.vavr.Predicates.instanceOf;

public class PatternMatchTest {

    @Test
    public void testMatchFailure() {
        var res = Try.of(() -> {
            throw new RuntimeException();
        });
        Match(res).of(
          // 匹配成功情况
                Case($Success($()), r -> run(Assert::fail)),
          // 匹配异常为 RuntimeException
                Case($Failure($(instanceOf(RuntimeException.class))), r -> true),
          // 匹配异常为 IllegalStateException
                Case($Failure($(instanceOf(IllegalStateException.class))), r -> run(Assert::fail)),
          // 匹配异常为 NullPointerException
                Case($Failure($(instanceOf(NullPointerException.class))), r -> run(Assert::fail)),
          // 匹配其余失败的情况
                Case($Failure($()), r -> run(Assert::fail))
        );
    }

    @Test
    public void testMatchSuccess() {
        var res = Try.of(() -> "Nice");
        Match(res).of(
          // 匹配任意成功的情况
                Case($Success($()), r -> run(() -> Assert.assertEquals("Nice", r))),
          // 匹配任意失败的情况
                Case($Failure($()), r -> run(Assert::fail))
        );
    }
}

复制代码//GO 
func BFSearch(haystack string, needle string) int { 
    l1 := len(haystack) 
    l2 := len(needle) 
    i, j := 0, 0 
    for i < l1 && j < l2 { 
        if haystack[i] == needle[j] { 
            i++ 
            j++
        } else {
            i -= j - 1
            j = 0
        }
    }
    if j == l2 {
        return i - j
    }
    return -1
}

复制代码 //GO 
func KmpSearch(haystack string, needle string, next []int) int { 
    l1 := len(haystack) 
    l2 := len(needle) 
    i, j := 0, 0 
    for i < l1 && j < l2 { 
        if j == -1 || haystack[i] == needle[j] { 
            i++
            j++
        } else {
            j = next[j]
        }
    }
    if j == l2 {
        return i - j
    }
    return -1
}

复制代码# clone code
git clone https://github.com/qishibo/AnotherRedisDesktopManager.git
cd AnotherRedisDesktopManager

# install dependencies
npm install

# if download electron failed during installing, use this command
# ELECTRON_MIRROR="https://npm.taobao.org/mirrors/electron/" npm install

# serve with hot reload at localhost:9988
npm start

# after the previous step is completed, open another tab, build up a desktop client
npm run electron

复制代码$ redis-server

复制代码$ redis-cli

复制代码$ config get requirepass

复制代码$ config set requirepass [new passward]

复制代码// config/db.ts
const productConfig = {
  mysql: {
    port: '数据库端口',
    host: '数据库地址',
    user: '用户名',
    password: '密码',
    database: 'nest_zero_to_one', // 库名
    connectionLimit: 10, // 连接限制
  },
+  redis: {
+    port: '线上 Redis 端口',
+    host: '线上 Redis 域名',
+    db: '库名',
+    password: 'Redis 访问密码',
+  }
};

const localConfig = {
  mysql: {
    port: '数据库端口',
    host: '数据库地址',
    user: '用户名',
    password: '密码',
    database: 'nest_zero_to_one', // 库名
    connectionLimit: 10, // 连接限制
  },
+  redis: {
+    port: 6379,
+    host: '127.0.0.1',
+    db: 0,
+    password: 'root',
+  }
};

// 本地运行是没有 process.env.NODE_ENV 的，借此来区分[开发环境]和[生产环境]
const config = process.env.NODE_ENV ? productConfig : localConfig;

export default config;

复制代码$ yarn add ioredis -S

复制代码// src/database/redis.ts
import * as Redis from 'ioredis';
import { Logger } from '../utils/log4js';
import config from '../../config/db';

let n: number = 0;
const redisIndex = []; // 用于记录 redis 实例索引
const redisList = []; // 用于存储 redis 实例

export class RedisInstance {
  static async initRedis(method: string, db: number = 0) {
    const isExist = redisIndex.some(x => x === db);
    if (!isExist) {
      Logger.debug(`[Redis ${db}]来自 ${method} 方法调用, Redis 实例化了 ${++n} 次 `);
      redisList[db] = new Redis({ ...config.redis, db });
      redisIndex.push(db);
    } else {
      Logger.debug(`[Redis ${db}]来自 ${method} 方法调用`);
    }
    return redisList[db];
  }
}

复制代码// src/logical/auth/auth.service.ts
import { Injectable } from '@nestjs/common';
import { UserService } from '../user/user.service';
import { JwtService } from '@nestjs/jwt';
import { encryptPassword } from '../../utils/cryptogram';
+ import { RedisInstance } from '../../database/redis';

@Injectable()
export class AuthService {
  constructor(private readonly usersService: UserService, private readonly jwtService: JwtService) {}

  // JWT验证 - Step 2: 校验用户信息
  async validateUser(username: string, password: string): Promise<any> {
    // console.log('JWT验证 - Step 2: 校验用户信息');
    const user = await this.usersService.findOne(username);
    if (user) {
      const hashedPassword = user.password;
      const salt = user.salt;
      const hashPassword = encryptPassword(password, salt);
      if (hashedPassword === hashPassword) {
        // 密码正确
        return {
          code: 1,
          user,
        };
      } else {
        // 密码错误
        return {
          code: 2,
          user: null,
        };
      }
    }
    // 查无此人
    return {
      code: 3,
      user: null,
    };
  }

  // JWT验证 - Step 3: 处理 jwt 签证
  async certificate(user: any) {
    const payload = {
      username: user.username,
-      sub: user.userId, // 之前笔误，写错了
+      sub: user.id,
      realName: user.realName,
      role: user.role,
    };
    // console.log('JWT验证 - Step 3: 处理 jwt 签证', `payload: ${JSON.stringify(payload)}`);
    try {
      const token = this.jwtService.sign(payload);
+      // 实例化 redis
+      const redis = await RedisInstance.initRedis('auth.certificate', 0);
+      // 将用户信息和 token 存入 redis，并设置失效时间，语法：[key, seconds, value]
+      await redis.setex(`${user.id}-${user.username}`, 300, `${token}`);
      return {
        code: 200,
        data: {
          token,
        },
        msg: `登录成功`,
      };
    } catch (error) {
      return {
        code: 600,
        msg: `账号或密码错误`,
      };
    }
  }
}

复制代码// src/guards/rbac.guard.ts
- import { CanActivate, ExecutionContext, Injectable, ForbiddenException } from '@nestjs/common';
+ import { CanActivate, ExecutionContext, Injectable, ForbiddenException, UnauthorizedException } from '@nestjs/common';
+ import { RedisInstance } from '../database/redis';

@Injectable()
export class RbacGuard implements CanActivate {
  // role[用户角色]: 0-超级管理员 | 1-管理员 | 2-开发&测试&运营 | 3-普通用户（只能查看）
  constructor(private readonly role: number) {}
  async canActivate(context: ExecutionContext): Promise<boolean> {
    const request = context.switchToHttp().getRequest();
    const user = request.user;

+    // 获取请求头里的 token
+    const authorization = request['headers'].authorization || void 0;
+    const token = authorization.split(' ')[1]; // authorization: Bearer xxx

+    // 获取 redis 里缓存的 token
+    const redis = await RedisInstance.initRedis('TokenGuard.canActivate', 0);
+    const key = `${user.userId}-${user.username}`;
+    const cache = await redis.get(key);

+    if (token !== cache) {
+      // 如果 token 不匹配，禁止访问
+      throw new UnauthorizedException('您的账号在其他地方登录，请重新登录');
+    }

    if (user.role > this.role) {
      // 如果权限不匹配，禁止访问
      throw new ForbiddenException('对不起，您无权操作');
    }
    return true;
  }
}

复制代码O(1)
$n=100000;
echo 'hello';

O(?)
$n=100000;
echo 'hello1';
echo 'hello2';
echo 'hello3';

复制代码O(n)
for($i = 1; $i <= $n; $i++) {
    echo 'hello';
}

O(n^2)
for($i = 1; $i <= $n; $i++) {
    for($j = 1; $j <= $n; $j++) {
        echo 'hello';
    }
}

复制代码O(log n)
for($i = 1; $i <= $n; $i = $i*2) {
    echo 'hello';
}

O(k^2)

fib($n) {
    if ($n < 2) {
        return $n;
    }
    
    return fib($n-1) + fib($n-2);
}

复制代码从1加到2一直加到n，求它的和

复制代码$sum = 0;
for ($i=1; $i <=$n; $i++) {
    $sum += $i;
}

复制代码y = n*(n+1)/2

复制代码Fib：0,1,1,2,3,5,8,13,21...

F(n) = F(n-1)+F(n-2)

复制代码fib($n) {
    if($n < 2) {
        retuen $n;
    }
    
    return fib($n-1)+fib($n-2);
}

复制代码<dependency>
  <groupId>net.coobird</groupId>
  <artifactId>thumbnailator</artifactId>
  <version>[0.4, 0.5)</version>
</dependency>

复制代码public class ImageUtils {
  /**
   * 根据指定大小压缩图片
   *
   * @param imageBytes 源图片字节数组
   * @param desFileSize 指定图片大小，单位kb
   * @param imageId 影像编号
   * @return 压缩质量后的图片字节数组
   */
  public static byte[] compressPicForScale(
      byte[] imageBytes, long desFileSize, String imageId, Double quality) {
    if (imageBytes == null || imageBytes.length <= 0 || imageBytes.length < desFileSize * 1024) {
      return imageBytes;
    }
    long srcSize = imageBytes.length;
    try {
      ByteArrayInputStream inputStream = new ByteArrayInputStream(imageBytes);
      ByteArrayOutputStream outputStream= new ByteArrayOutputStream(imageBytes.length);
      Thumbnails.of(inputStream).scale(1f).outputQuality(quality).toOutputStream(outputStream);
      imageBytes = outputStream.toByteArray();
      log.info(
          "【图片压缩】imageId={} | 图片原大小={}kb | 压缩后大小={}kb",
          imageId,
          srcSize / 1024,
          imageBytes.length / 1024);
    } catch (Exception e) {
      log.error("【图片压缩】msg=图片压缩失败!", e);
    }
    return imageBytes;
  }
}

复制代码public static boolean compressPic(String srcFilePath, String descFilePath) throws IOException {
    File file = null;
    BufferedImage src = null;
    FileOutputStream out = null;
    ImageWriter imgWrier;
    ImageWriteParam imgWriteParams;

    // 指定写图片的方式为 jpg
    imgWrier = ImageIO.getImageWritersByFormatName("jpg").next();
    imgWriteParams = new javax.imageio.plugins.jpeg.JPEGImageWriteParam(
            null);
    // 要使用压缩，必须指定压缩方式为MODE_EXPLICIT
    imgWriteParams.setCompressionMode(imgWriteParams.MODE_EXPLICIT);
    // 这里指定压缩的程度，参数qality是取值0~1范围内，
    imgWriteParams.setCompressionQuality((float)1);
    imgWriteParams.setProgressiveMode(imgWriteParams.MODE_DISABLED);
    ColorModel colorModel = ImageIO.read(new File(srcFilePath)).getColorModel();// ColorModel.getRGBdefault();
    // 指定压缩时使用的色彩模式
    // imgWriteParams.setDestinationType(new javax.imageio.ImageTypeSpecifier(
    // colorModel, colorModel.createCompatibleSampleModel(16, 16)));
    imgWriteParams.setDestinationType(new javax.imageio.ImageTypeSpecifier(
    colorModel, colorModel.createCompatibleSampleModel(16, 16)));
    try {
        if (isBlank(srcFilePath)) {
            return false;
        } else {
            file = new File(srcFilePath);
            System.out.println(file.length());
            src = ImageIO.read(file);
            out = new FileOutputStream(descFilePath);

            imgWrier.reset();
            // 必须先指定 out值，才能调用write方法, ImageOutputStream可以通过任何
            // OutputStream构造
            imgWrier.setOutput(ImageIO.createImageOutputStream(out));
            // 调用write方法，就可以向输入流写图片
            imgWrier.write(null, new IIOImage(src, null, null),
                    imgWriteParams);
            out.flush();
            out.close();
        }
    } catch (Exception e) {
        e.printStackTrace();
        return false;
    }
    return true;
}

public static boolean isBlank(String string) {
    if (string == null || string.length() == 0 || string.trim().equals("")) {
        return true;
    }
    return false;
}

复制代码<!--整合Knife4j-->
<dependency>
    <groupId>com.github.xiaoymin</groupId>
    <artifactId>knife4j-spring-boot-starter</artifactId>
    <version>2.0.4</version>
</dependency>

复制代码/**
 * Swagger2API文档的配置
 */
@Configuration
@EnableSwagger2
@EnableKnife4j
public class Swagger2Config {
    
}

复制代码/**
 * 品牌管理Controller
 * Created by macro on 2019/4/19.
 */
@Api(tags = "PmsBrandController", description = "商品品牌管理")
@Controller
@RequestMapping("/brand")
public class PmsBrandController {
    @Autowired
    private PmsBrandService brandService;

    private static final Logger LOGGER = LoggerFactory.getLogger(PmsBrandController.class);

    @ApiOperation("添加品牌")
    @ApiOperationSupport(ignoreParameters = {"id","productCount","productCommentCount"})
    @RequestMapping(value = "/create", method = RequestMethod.POST)
    @ResponseBody
    public CommonResult createBrand(@RequestBody PmsBrand pmsBrand) {
        CommonResult commonResult;
        int count = brandService.createBrand(pmsBrand);
        if (count == 1) {
            commonResult = CommonResult.success(pmsBrand);
            LOGGER.debug("createBrand success:{}", pmsBrand);
        } else {
            commonResult = CommonResult.failed("操作失败");
            LOGGER.debug("createBrand failed:{}", pmsBrand);
        }
        return commonResult;
    }
}