CompletableFuture原理与实践-外卖商家端API的异步化-51CTO.COM

ExecutorService executor = Executors.newFixedThreadPool(5);
ListeningExecutorService guavaExecutor = MoreExecutors.listeningDecorator(executor);ListenableFuture<String> future1 = guavaExecutor.submit(() -> {
    //step 1
    System.out.println("执行step 1");
    return "step1 result";
});
ListenableFuture<String> future2 = guavaExecutor.submit(() -> {
    //step 2
    System.out.println("执行step 2");
    return "step2 result";
});
ListenableFuture<List<String>> future1And2 = Futures.allAsList(future1, future2);
Futures.addCallback(future1And2, new FutureCallback<List<String>>() {
    @Override
    public void onSuccess(List<String> result) {
        System.out.println(result);
        ListenableFuture<String> future3 = guavaExecutor.submit(() -> {
            System.out.println("执行step 3");
            return "step3 result";
        });
        Futures.addCallback(future3, new FutureCallback<String>() {
            @Override
            public void onSuccess(String result) {
                System.out.println(result);
            }        
            @Override
            public void onFailure(Throwable t) {
            }
        }, guavaExecutor);
    }

    @Override
    public void onFailure(Throwable t) {
    }}, guavaExecutor);

ExecutorService executor = Executors.newFixedThreadPool(5);
CompletableFuture<String> cf1 = CompletableFuture.supplyAsync(() -> {
    System.out.println("执行step 1");
    return "step1 result";
}, executor);
CompletableFuture<String> cf2 = CompletableFuture.supplyAsync(() -> {
    System.out.println("执行step 2");
    return "step2 result";
});
cf1.thenCombine(cf2, (result1, result2) -> {
    System.out.println(result1 + " , " + result2);
    System.out.println("执行step 3");
    return "step3 result";
}).thenAccept(result3 -> System.out.println(result3));

ExecutorService executor = Executors.newFixedThreadPool(5);
//1、使用runAsync或supplyAsync发起异步调用
CompletableFuture<String> cf1 = CompletableFuture.supplyAsync(() -> {
  return "result1";
}, executor);
//2、CompletableFuture.completedFuture()直接创建一个已完成状态的CompletableFuture
CompletableFuture<String> cf2 = CompletableFuture.completedFuture("result2");
//3、先初始化一个未完成的CompletableFuture，然后通过complete()、completeExceptionally()，完成该CompletableFuture
CompletableFuture<String> cf = new CompletableFuture<>();
cf.complete("success");

@FunctionalInterface
public interface ThriftAsyncCall {
    void invoke() throws TException;
}
 /**
  * 该方法为美团内部rpc注册监听的封装，可以作为其他实现的参照
  * OctoThriftCallback 为thrift回调方法
  * ThriftAsyncCall 为自定义函数，用来表示一次thrift调用（定义如上）
  */
  public static <T> CompletableFuture<T> toCompletableFuture(final OctoThriftCallback<?,T> callback , ThriftAsyncCall thriftCall) {
   //新建一个未完成的CompletableFuture
   CompletableFuture<T> resultFuture = new CompletableFuture<>();
   //监听回调的完成，并且与CompletableFuture同步状态
   callback.addObserver(new OctoObserver<T>() {
       @Override
       public void onSuccess(T t) {
           resultFuture.complete(t);
       }
       @Override
       public void onFailure(Throwable throwable) {
           resultFuture.completeExceptionally(throwable);
       }
   });
   if (thriftCall != null) {
       try {
           thriftCall.invoke();
       } catch (TException e) {
           resultFuture.completeExceptionally(e);
       }
   }
   return resultFuture;
  }

CompletableFuture<String> cf3 = cf1.thenApply(result1 -> {
  //result1为CF1的结果
  //......
  return "result3";
});
CompletableFuture<String> cf5 = cf2.thenApply(result2 -> {
  //result2为CF2的结果
  //......
  return "result5";
});

CompletableFuture<String> cf4 = cf1.thenCombine(cf2, (result1, result2) -> {
  //result1和result2分别为cf1和cf2的结果
  return "result4";
});

CompletableFuture<Void> cf6 = CompletableFuture.allOf(cf3, cf4, cf5);
CompletableFuture<String> result = cf6.thenApply(v -> {
  //这里的join并不会阻塞，因为传给thenApply的函数是在CF3、CF4、CF5全部完成时，才会执行 。
  result3 = cf3.join();
  result4 = cf4.join();
  result5 = cf5.join();
  //根据result3、result4、result5组装最终result;
  return "result";
});

ExecutorService threadPool1 = new ThreadPoolExecutor(10, 10, 0L, TimeUnit.MILLISECONDS, new ArrayBlockingQueue<>(100));
CompletableFuture<String> future1 = CompletableFuture.supplyAsync(() -> {
    System.out.println("supplyAsync 执行线程：" + Thread.currentThread().getName());
    //业务操作
    return "";
}, threadPool1);
//此时，如果future1中的业务操作已经执行完毕并返回，则该thenApply直接由当前main线程执行；否则，将会由执行以上业务操作的threadPool1中的线程执行。
future1.thenApply(value -> {
    System.out.println("thenApply 执行线程：" + Thread.currentThread().getName());
    return value + "1";
});
//使用ForkJoinPool中的共用线程池CommonPool
future1.thenApplyAsync(value -> {
//do something
  return value + "1";
});
//使用指定线程池
future1.thenApplyAsync(value -> {
//do something
  return value + "1";
}, threadPool1);

public Object doGet() {
  ExecutorService threadPool1 = new ThreadPoolExecutor(10, 10, 0L, TimeUnit.MILLISECONDS, new ArrayBlockingQueue<>(100));
  CompletableFuture cf1 = CompletableFuture.supplyAsync(() -> {
  //do sth
    return CompletableFuture.supplyAsync(() -> {
        System.out.println("child");
        return "child";
      }, threadPool1).join();//子任务
    }, threadPool1);
  return cf1.join();
}

@Autowired
private WmOrderAdditionInfoThriftService wmOrderAdditionInfoThriftService;//内部接口
public CompletableFuture<Integer> getCancelTypeAsync(long orderId) {
    CompletableFuture<WmOrderOpRemarkResult> remarkResultFuture = wmOrderAdditionInfoThriftService.findOrderCancelledRemarkByOrderIdAsync(orderId);//业务方法，内部会发起异步rpc调用
    return remarkResultFuture
      .exceptionally(err -> {//通过exceptionally 捕获异常，打印日志并返回默认值
         log.error("WmOrderRemarkService.getCancelTypeAsync Exception orderId={}", orderId, err);
         return 0;
      });
}

@Autowired
private WmOrderAdditionInfoThriftService wmOrderAdditionInfoThriftService;//内部接口
public CompletableFuture<Integer> getCancelTypeAsync(long orderId) {
    CompletableFuture<WmOrderOpRemarkResult> remarkResultFuture = wmOrderAdditionInfoThriftService.findOrderCancelledRemarkByOrderIdAsync(orderId);//业务方法，内部会发起异步rpc调用
    return remarkResultFuture
          .thenApply(result -> {//这里增加了一个回调方法thenApply，如果发生异常thenApply内部会通过new CompletionException(throwable) 对异常进行包装
      //这里是一些业务操作
        })
      .exceptionally(err -> {//通过exceptionally 捕获异常，这里的err已经被thenApply包装过，因此需要通过Throwable.getCause()提取异常
         log.error("WmOrderRemarkService.getCancelTypeAsync Exception orderId={}", orderId, ExceptionUtils.extractRealException(err));
         return 0;
      });
}

public class ExceptionUtils {
    public static Throwable extractRealException(Throwable throwable) {
          //这里判断异常类型是否为CompletionException、ExecutionException，如果是则进行提取，否则直接返回。
        if (throwable instanceof CompletionException || throwable instanceof ExecutionException) {
            if (throwable.getCause() != null) {
                return throwable.getCause();
            }
        }
        return throwable;
    }
}

@FunctionalInterface
public interface ThriftAsyncCall {
    void invoke() throws TException ;
}

/**
 * CompletableFuture封装工具类
 */
@Slf4j
public class FutureUtils {
/**
 * 该方法为美团内部rpc注册监听的封装，可以作为其他实现的参照
 * OctoThriftCallback 为thrift回调方法
 * ThriftAsyncCall 为自定义函数，用来表示一次thrift调用（定义如上）
 */
public static <T> CompletableFuture<T> toCompletableFuture(final OctoThriftCallback<?,T> callback , ThriftAsyncCall thriftCall) {
    CompletableFuture<T> thriftResultFuture = new CompletableFuture<>();
    callback.addObserver(new OctoObserver<T>() {
        @Override
        public void onSuccess(T t) {
            thriftResultFuture.complete(t);
        }
        @Override
        public void onFailure(Throwable throwable) {
            thriftResultFuture.completeExceptionally(throwable);
        }
    });
    if (thriftCall != null) {
        try {
            thriftCall.invoke();
        } catch (TException e) {
            thriftResultFuture.completeExceptionally(e);
        }
    }
    return thriftResultFuture;
}
  /**
   * 设置CF状态为失败
   */
  public static <T> CompletableFuture<T> failed(Throwable ex) {
   CompletableFuture<T> completableFuture = new CompletableFuture<>();
   completableFuture.completeExceptionally(ex);
   return completableFuture;
  }
  /**
   * 设置CF状态为成功
   */
  public static <T> CompletableFuture<T> success(T result) {
   CompletableFuture<T> completableFuture = new CompletableFuture<>();
   completableFuture.complete(result);
   return completableFuture;
  }
  /**
   * 将List<CompletableFuture<T>> 转为 CompletableFuture<List<T>>
   */
  public static <T> CompletableFuture<List<T>> sequence(Collection<CompletableFuture<T>> completableFutures) {
   return CompletableFuture.allOf(completableFutures.toArray(new CompletableFuture<?>[0]))
           .thenApply(v -> completableFutures.stream()
                   .map(CompletableFuture::join)
                   .collect(Collectors.toList())
           );
  }
  /**
   * 将List<CompletableFuture<List<T>>> 转为 CompletableFuture<List<T>>
   * 多用于分页查询的场景
   */
  public static <T> CompletableFuture<List<T>> sequenceList(Collection<CompletableFuture<List<T>>> completableFutures) {
   return CompletableFuture.allOf(completableFutures.toArray(new CompletableFuture<?>[0]))
           .thenApply(v -> completableFutures.stream()
                   .flatMap( listFuture -> listFuture.join().stream())
                   .collect(Collectors.toList())
           );
  }
  /*
   * 将List<CompletableFuture<Map<K, V>>> 转为 CompletableFuture<Map<K, V>>
   * @Param mergeFunction 自定义key冲突时的merge策略
   */
  public static <K, V> CompletableFuture<Map<K, V>> sequenceMap(
       Collection<CompletableFuture<Map<K, V>>> completableFutures, BinaryOperator<V> mergeFunction) {
   return CompletableFuture
           .allOf(completableFutures.toArray(new CompletableFuture<?>[0]))
           .thenApply(v -> completableFutures.stream().map(CompletableFuture::join)
                   .flatMap(map -> map.entrySet().stream())
                   .collect(Collectors.toMap(Entry::getKey, Entry::getValue, mergeFunction)));
  }
  /**
   * 将List<CompletableFuture<T>> 转为 CompletableFuture<List<T>>，并过滤调null值
   */
  public static <T> CompletableFuture<List<T>> sequenceNonNull(Collection<CompletableFuture<T>> completableFutures) {
   return CompletableFuture.allOf(completableFutures.toArray(new CompletableFuture<?>[0]))
           .thenApply(v -> completableFutures.stream()
                   .map(CompletableFuture::join)
                   .filter(e -> e != null)
                   .collect(Collectors.toList())
           );
  }
  /**
   * 将List<CompletableFuture<List<T>>> 转为 CompletableFuture<List<T>>，并过滤调null值
   * 多用于分页查询的场景
   */
  public static <T> CompletableFuture<List<T>> sequenceListNonNull(Collection<CompletableFuture<List<T>>> completableFutures) {
   return CompletableFuture.allOf(completableFutures.toArray(new CompletableFuture<?>[0]))
           .thenApply(v -> completableFutures.stream()
                   .flatMap( listFuture -> listFuture.join().stream().filter(e -> e != null))
                   .collect(Collectors.toList())
           );
  }
  /**
   * 将List<CompletableFuture<Map<K, V>>> 转为 CompletableFuture<Map<K, V>>
   * @Param filterFunction 自定义过滤策略
   */
  public static <T> CompletableFuture<List<T>> sequence(Collection<CompletableFuture<T>> completableFutures,
                                                     Predicate<? super T> filterFunction) {
   return CompletableFuture.allOf(completableFutures.toArray(new CompletableFuture<?>[0]))
           .thenApply(v -> completableFutures.stream()
                   .map(CompletableFuture::join)
                   .filter(filterFunction)
                   .collect(Collectors.toList())
           );
  }
  /**
   * 将List<CompletableFuture<List<T>>> 转为 CompletableFuture<List<T>>
   * @Param filterFunction 自定义过滤策略
   */
  public static <T> CompletableFuture<List<T>> sequenceList(Collection<CompletableFuture<List<T>>> completableFutures,
                                                         Predicate<? super T> filterFunction) {
   return CompletableFuture.allOf(completableFutures.toArray(new CompletableFuture<?>[0]))
           .thenApply(v -> completableFutures.stream()
                   .flatMap( listFuture -> listFuture.join().stream().filter(filterFunction))
                   .collect(Collectors.toList())
           );
  }
/**
 * 将CompletableFuture<Map<K,V>>的list转为 CompletableFuture<Map<K,V>>。 多个map合并为一个map。 如果key冲突，采用新的value覆盖。
 */
  public static <K, V> CompletableFuture<Map<K, V>> sequenceMap(
       Collection<CompletableFuture<Map<K, V>>> completableFutures) {
   return CompletableFuture
           .allOf(completableFutures.toArray(new CompletableFuture<?>[0]))
           .thenApply(v -> completableFutures.stream().map(CompletableFuture::join)
                   .flatMap(map -> map.entrySet().stream())
                   .collect(Collectors.toMap(Entry::getKey, Entry::getValue, (a, b) -> b)));
  }}

  public class ExceptionUtils {
   /**
    * 提取真正的异常
    */
   public static Throwable extractRealException(Throwable throwable) {
       if (throwable instanceof CompletionException || throwable instanceof ExecutionException) {
           if (throwable.getCause() != null) {
               return throwable.getCause();
           }
       }
       return throwable;
   }
  }

  @Slf4j
  public abstract class AbstractLogAction<R> {
  protected final String methodName;
  protected final Object[] args;
public AbstractLogAction(String methodName, Object... args) {
    this.methodName = methodName;
    this.args = args;
}
protected void logResult(R result, Throwable throwable) {
    if (throwable != null) {
        boolean isBusinessError = throwable instanceof TBase || (throwable.getCause() != null && throwable
                .getCause() instanceof TBase);
        if (isBusinessError) {
            logBusinessError(throwable);
        } else if (throwable instanceof DegradeException || throwable instanceof DegradeRuntimeException) {//这里为内部rpc框架抛出的异常，使用时可以酌情修改
            if (RhinoSwitch.getBoolean("isPrintDegradeLog", false)) {
                log.error("{} degrade exception, param:{} , error:{}", methodName, args, throwable);
            }
        } else {
            log.error("{} unknown error, param:{} , error:{}", methodName, args, ExceptionUtils.extractRealException(throwable));
        }
    } else {
        if (isLogResult()) {
            log.info("{} param:{} , result:{}", methodName, args, result);
        } else {
            log.info("{} param:{}", methodName, args);
        }
    }
}
private void logBusinessError(Throwable throwable) {
    log.error("{} business error, param:{} , error:{}", methodName, args, throwable.toString(), ExceptionUtils.extractRealException(throwable));
}
private boolean isLogResult() {
      //这里是动态配置开关，用于动态控制日志打印，开源动态配置中心可以使用nacos、apollo等，如果项目没有使用配置中心则可以删除
    return RhinoSwitch.getBoolean(methodName + "_isLogResult", false);
}}

/**
 * 发生异常时，根据是否为业务异常打印日志。
 * 跟CompletableFuture.whenComplete配合使用，不改变completableFuture的结果（正常OR异常）
 */
@Slf4j
public class LogErrorAction<R> extends AbstractLogAction<R> implements BiConsumer<R, Throwable> {
public LogErrorAction(String methodName, Object... args) {
    super(methodName, args);
}
@Override
public void accept(R result, Throwable throwable) {
    logResult(result, throwable);
}
}

completableFuture
.whenComplete(
  new LogErrorAction<>("orderService.getOrder", params));

/**
 * 当发生异常时返回自定义的值
 */
public class DefaultValueHandle<R> extends AbstractLogAction<R> implements BiFunction<R, Throwable, R> {
    private final R defaultValue;
/**
 * 当返回值为空的时候是否替换为默认值
 */
private final boolean isNullToDefault;
/**
 * @param methodName      方法名称
 * @param defaultValue 当异常发生时自定义返回的默认值
 * @param args            方法入参
 */
  public DefaultValueHandle(String methodName, R defaultValue, Object... args) {
   super(methodName, args);
   this.defaultValue = defaultValue;
   this.isNullToDefault = false;
  }
/**
 * @param isNullToDefault
 * @param defaultValue 当异常发生时自定义返回的默认值
 * @param methodName      方法名称
 * @param args            方法入参
 */
  public DefaultValueHandle(boolean isNullToDefault, R defaultValue, String methodName, Object... args) {
   super(methodName, args);
   this.defaultValue = defaultValue;
   this.isNullToDefault = isNullToDefault;
  }
@Override
public R apply(R result, Throwable throwable) {
    logResult(result, throwable);
    if (throwable != null) {
        return defaultValue;
    }
    if (result == null && isNullToDefault) {
        return defaultValue;
    }
    return result;
}
public static <R> DefaultValueHandle.DefaultValueHandleBuilder<R> builder() {
    return new DefaultValueHandle.DefaultValueHandleBuilder<>();
}
public static class DefaultValueHandleBuilder<R> {
    private boolean isNullToDefault;
    private R defaultValue;
    private String methodName;
    private Object[] args;
    DefaultValueHandleBuilder() {
    }
    public DefaultValueHandle.DefaultValueHandleBuilder<R> isNullToDefault(final boolean isNullToDefault) {
        this.isNullToDefault = isNullToDefault;
        return this;
    }
    public DefaultValueHandle.DefaultValueHandleBuilder<R> defaultValue(final R defaultValue) {
        this.defaultValue = defaultValue;
        return this;
    }
    public DefaultValueHandle.DefaultValueHandleBuilder<R> methodName(final String methodName) {
        this.methodName = methodName;
        return this;
    }
    public DefaultValueHandle.DefaultValueHandleBuilder<R> args(final Object... args) {
        this.args = args;
        return this;
    }
    public DefaultValueHandle<R> build() {
        return new DefaultValueHandle<R>(this.isNullToDefault, this.defaultValue, this.methodName, this.args);
    }
    public String toString() {
        return "DefaultValueHandle.DefaultValueHandleBuilder(isNullToDefault=" + this.isNullToDefault + ", defaultValue=" + this.defaultValue + ", methodName=" + this.methodName + ", args=" + Arrays.deepToString(this.args) + ")";
    }
}

completableFuture.handle(new DefaultValueHandle<>("orderService.getOrder", Collections.emptyMap(), params));