CompletableFuture常见用法
一般使用场景
合并两个接口返回数据
适合 合并显示两个服务或者多个接口查询到的数据等，提高程序效率。
public class Test {
public static void main(String[] args) {
long startTime = System.currentTimeMillis();
List<Bean> join = CompletableFuture.supplyAsync(() -> {
try {
// 模拟调用接口A 耗时2秒
Thread.sleep(2000);
} catch (InterruptedException e1) {
e1.printStackTrace();
}
List<Bean> beans = new ArrayList<>();
beans.add(new Bean(1, "111"));
beans.add(new Bean(2, "222"));
return beans;
}).thenCombine(CompletableFuture.supplyAsync(() -> {
try {
// 模拟调用接口B 耗时2秒
Thread.sleep(2000);
} catch (InterruptedException e1) {
e1.printStackTrace();
}
List<Bean> beans = new ArrayList<>();
beans.add(new Bean(3, "333"));
beans.add(new Bean(4, "444"));
return beans;
}), (a, b) -> {
// 两个接口数据合并
a.addAll(b);
return a;
}).join();
System.out.println(join);
System.out.println(System.currentTimeMillis() - startTime);
}
@Data
@AllArgsConstructor
public static class Bean {
private Integer id;
private String value;
}
}
输出
[ListTest.Bean(id=1, value=111), ListTest.Bean(id=2, value=222), ListTest.Bean(id=3, value=333), ListTest.Bean(id=4, value=444)]
2010
同时处理两段逻辑
以下模拟，当A业务且B业务执行完毕后输出：我也执行了
public class Test {
public static void main(String[] args) throws ExecutionException, InterruptedException {
CompletableFuture.allOf(CompletableFuture.runAsync(() -> {
try {
// 模拟处理业务 A
Thread.sleep(2000);
} catch (InterruptedException e1) {
e1.printStackTrace();
}
}), CompletableFuture.runAsync(() -> {
try {
// 模拟处理业务 B
Thread.sleep(2000);
} catch (InterruptedException e1) {
e1.printStackTrace();
}
})).get();
System.out.println("我也执行了");
}
}
模拟批量处理数据
大量数据处理，适合Excel文件数据处理。
public class Test {
public static void main(String[] args) throws ExecutionException, InterruptedException {
long startTime = System.currentTimeMillis();
List<String> urls = Arrays.asList("url1", "url2", "url3", "url4");
List<CompletableFuture<String>> completableFutures = urls.stream().map(m -> {
//并行查询接口数据文本
return CompletableFuture.supplyAsync(() -> {
try {
// 模拟调用接口
Thread.sleep(2000);
} catch (InterruptedException e) {
e.printStackTrace();
}
return m + "我是查询到的数据";
});
}).collect(Collectors.toList());
CompletableFuture<List<String>> listCompletableFuture = CompletableFuture.allOf(completableFutures.toArray(new CompletableFuture[0])).
thenApply(t -> completableFutures.stream().map(CompletableFuture::join)
.filter(f -> {
// 模拟需要过滤掉的数据
return !f.startsWith("url2");
})
.collect(Collectors.toList()));
System.out.println(listCompletableFuture.get());
System.out.println(System.currentTimeMillis() - startTime);
}
}
返回
[url1我是查询到的数据, url3我是查询到的数据, url4我是查询到的数据]
2010
帮助
CompletableFuture执行出错不出现异常信息？
看如下代码进行异步操作时，竟然没有打印出任何异常信息
CompletableFuture.runAsync(()->{
System.out.println("开始执行");
System.out.println(1/0);
});
输出
开始执行
如果需要获取程序出现的异常可以用以下方式：
CompletableFuture.runAsync(()->{
System.out.println("开始执行");
System.out.println(1/0);
}).exceptionally(e->{
e.printStackTrace();
return null;
});
输出
开始执行
java.util.concurrent.CompletionException: java.lang.ArithmeticException: / by zero
at java.base/java.util.concurrent.CompletableFuture.encodeThrowable(CompletableFuture.java:314)
at java.base/java.util.concurrent.CompletableFuture.completeThrowable(CompletableFuture.java:319)
at java.base/java.util.concurrent.CompletableFuture$AsyncRun.run(CompletableFuture.java:1739)
at java.base/java.util.concurrent.CompletableFuture$AsyncRun.exec(CompletableFuture.java:1728)
at java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:290)
at java.base/java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(ForkJoinPool.java:1020)
at java.base/java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1656)
at java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1594)
at java.base/java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:183)
Caused by: java.lang.ArithmeticException: / by zero
at test.lambda$main$1(TerminalBaseDetailedServiceImpl.java:80)
at java.base/java.util.concurrent.CompletableFuture$AsyncRun.run(CompletableFuture.java:1736)
... 6 more