写在前面的话
哈喽，好久不见，你们还好吗？
今天给大家带来的是我在实际项目上遇到的一个问题。
流程大致是，调用接口，然后将接口返回的数据更新一份到本地数据库，然后返回给前端。更新到本地数据库这个操作原本是用的异步。
国庆回老家，公司打电话来，前端转几秒的圈圈，然后无数据。经查，是Redis出了问题，用不了。
什么意思？
从接口请求到的数据，更新到本地数据库，这里有一个策略，先将数据放到Redis中，然后进行对比，如果不一致，再更新。Redis不可用，那么都查询数据库，就会很慢，前端请求接口一般是5s超时。
如果是异步，也就不会出现这个问题了。
所以，我们就先看看当时，我的代码明明是异步的，为什么没有生效呢？
@Async无效
先看一个例子。
Controller代码如下：
<pre mdtype="fences" cid="n31" lang="java" class="md-fences md-end-block ty-contain-cm modeLoaded" spellcheck="false" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">@GetMapping("/invalid")
public String invalidAsyncExample() {
iTestAsyncService.invalidAsyncExample();
return "测试完成 " + LocalDateTime.now().toString();
}</pre>
Service代码如下：
<pre mdtype="fences" cid="n35" lang="java" class="md-fences md-end-block ty-contain-cm modeLoaded" spellcheck="false" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">@Override
public void invalidAsyncExample() {
log.info("流程-1-{}", Thread.currentThread().getId());
invalidAsyncTask();
log.info("流程-3-{}", Thread.currentThread().getId());
}</pre>
Async代码如下：
<pre mdtype="fences" cid="n43" lang="java" class="md-fences md-end-block ty-contain-cm modeLoaded" spellcheck="false" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">@Async
public void invalidAsyncTask() {
try {
Thread.sleep(2000);
} catch (InterruptedException e) {
e.printStackTrace();
}
log.info("流程-2-{}", Thread.currentThread().getId());
}</pre>
执行结果：
<pre mdtype="fences" cid="n49" lang="" class="md-fences md-end-block ty-contain-cm modeLoaded" spellcheck="false" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">2020-11-11 21:14:06.784 INFO 13592 --- [nio-8080-exec-1] c.f.s.a.s.impl.TestAsyncServiceImpl : 流程-1-125
2020-11-11 21:14:08.785 INFO 13592 --- [nio-8080-exec-1] c.f.s.a.s.impl.TestAsyncServiceImpl : 流程-2-125
2020-11-11 21:14:08.785 INFO 13592 --- [nio-8080-exec-1] c.f.s.a.s.impl.TestAsyncServiceImpl : 流程-3-125</pre>
结果分析：确实是同步执行，没什么明明加了@Async的，异步没生效呢？
带这个这样一个疑问，在百度上寻找答案。同时，也决定阅读这一块的源码。想看一下，这个异步到底是怎么实现的。
通过阅读源码，会发现，Spring默认是用代理实现异步的。
什么意思？
你可以这样理解，你调用的类需要Spring帮你代理，然后才能异步去执行。
上面的示例代码，invalidAsyncTask(); 调用的方法很明确，不需要代理，这时候Spring也就不能帮你异步去执行了。
关于源码分析，后面在写源码博文的时候，再来。
无返回值的异步任务
首先呢，需要 @EnableAsync
Controller：
<pre mdtype="fences" cid="n105" lang="java" class="md-fences md-end-block ty-contain-cm modeLoaded" spellcheck="false" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">@GetMapping("/no-value")
public String noValueAsyncExample() {
iTestAsyncService.noValueAsyncExample();
return "测试完成 " + LocalDateTime.now().toString();
}</pre>
Service：
<pre mdtype="fences" cid="n111" lang="java" class="md-fences md-end-block ty-contain-cm modeLoaded" spellcheck="false" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">@Override
public void noValueAsyncExample() {
log.info("流程-1-{}", Thread.currentThread().getId());
iAsyncService.exampleTask();
log.info("流程-3-{}", Thread.currentThread().getId());
}</pre>
耗时任务：
<pre mdtype="fences" cid="n117" lang="java" class="md-fences md-end-block ty-contain-cm modeLoaded" spellcheck="false" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">@Override
public void exampleTask() {
try {
Thread.sleep(2000);
} catch (InterruptedException e) {
e.printStackTrace();
}
log.info("耗时任务-2-{}", Thread.currentThread().getId());
}</pre>
Async：
<pre mdtype="fences" cid="n123" lang="java" class="md-fences md-end-block ty-contain-cm modeLoaded" spellcheck="false" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">@Override
@Async
public void exampleTask() {
iTestAsyncService.exampleTask();
}</pre>
这里要注意，因为我们把耗时的任务放在同一个service里面，所以就会产生循环依赖的问题，需要用到 @Lazy 。
测试结果：
<pre mdtype="fences" cid="n134" lang="" class="md-fences md-end-block ty-contain-cm modeLoaded" spellcheck="false" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">2020-11-11 22:32:50.019 INFO 18888 --- [nio-8080-exec-7] c.f.s.a.s.impl.TestAsyncServiceImpl : 流程-1-131
2020-11-11 22:32:50.020 INFO 18888 --- [nio-8080-exec-7] c.f.s.a.s.impl.TestAsyncServiceImpl : 流程-3-131
2020-11-11 22:32:52.021 INFO 18888 --- [ task-9] c.f.s.a.s.impl.TestAsyncServiceImpl : 耗时任务-2-152</pre>
有返回值的异步任务
也是需要 @EnableAsync
Controller：
<pre mdtype="fences" cid="n148" lang="java" class="md-fences md-end-block ty-contain-cm modeLoaded" spellcheck="false" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">@GetMapping("/value")
public int valueAsyncExample() {
return iTestAsyncService.valueAsyncExample();
}</pre>
Service：
<pre mdtype="fences" cid="n156" lang="java" class="md-fences md-end-block ty-contain-cm modeLoaded" spellcheck="false" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">@Override
public int valueAsyncExample() {
int result = 0;
long startTime = System.currentTimeMillis();
List<Future<Integer>> futureList = new ArrayList<>();
for (int i = 0; i < 10; i++) {
Future<Integer> future = iAsyncService.addTask(i);
futureList.add(future);
}
for (Future<Integer> f : futureList) {
Integer value = null;
try {
value = f.get();
} catch (InterruptedException | ExecutionException e) {
e.printStackTrace();
}
if (value != null)
result += value;
}
long endTime = System.currentTimeMillis();
log.info("耗时 {} s", (endTime - startTime) / 1000D);
return result;
}</pre>
任务：
<pre mdtype="fences" cid="n162" lang="java" class="md-fences md-end-block ty-contain-cm modeLoaded" spellcheck="false" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">@Override
public Future<Integer> addTask(int n) {
try {
Thread.sleep(2000);
} catch (InterruptedException e) {
e.printStackTrace();
}
log.info("计算任务-{}", Thread.currentThread().getId());
return AsyncResult.forValue(n + 2);
}</pre>
Async：
<pre mdtype="fences" cid="n168" lang="java" class="md-fences md-end-block ty-contain-cm modeLoaded" spellcheck="false" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">@Override
@Async
public Future<Integer> addTask(int i) {
return iTestAsyncService.addTask(i);
}</pre>
同样，这里要注意，因为我们把耗时的任务放在同一个service里面，所以就会产生循环依赖的问题，需要用到 @Lazy 。
测试结果：
<pre mdtype="fences" cid="n178" lang="" class="md-fences md-end-block ty-contain-cm modeLoaded" spellcheck="false" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">2020-11-11 22:27:05.152 INFO 18888 --- [ task-3] c.f.s.a.s.impl.TestAsyncServiceImpl : 计算任务-146
2020-11-11 22:27:05.152 INFO 18888 --- [ task-5] c.f.s.a.s.impl.TestAsyncServiceImpl : 计算任务-148
2020-11-11 22:27:05.152 INFO 18888 --- [ task-4] c.f.s.a.s.impl.TestAsyncServiceImpl : 计算任务-147
2020-11-11 22:27:05.152 INFO 18888 --- [ task-6] c.f.s.a.s.impl.TestAsyncServiceImpl : 计算任务-149
2020-11-11 22:27:05.153 INFO 18888 --- [ task-7] c.f.s.a.s.impl.TestAsyncServiceImpl : 计算任务-150
2020-11-11 22:27:05.152 INFO 18888 --- [ task-2] c.f.s.a.s.impl.TestAsyncServiceImpl : 计算任务-145
2020-11-11 22:27:05.153 INFO 18888 --- [ task-8] c.f.s.a.s.impl.TestAsyncServiceImpl : 计算任务-151
2020-11-11 22:27:05.152 INFO 18888 --- [ task-1] c.f.s.a.s.impl.TestAsyncServiceImpl : 计算任务-144
2020-11-11 22:27:07.154 INFO 18888 --- [ task-6] c.f.s.a.s.impl.TestAsyncServiceImpl : 计算任务-149
2020-11-11 22:27:07.154 INFO 18888 --- [ task-3] c.f.s.a.s.impl.TestAsyncServiceImpl : 计算任务-146
2020-11-11 22:27:07.154 INFO 18888 --- [nio-8080-exec-1] c.f.s.a.s.impl.TestAsyncServiceImpl : 耗时 4.006 s</pre>
页面结果
<pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="" cid="n185" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 0px; margin-top: 0px; width: inherit;">65</pre>
测试代码
https://github.com/fengwenyi/study-spring-boot/tree/master/spring-boot-async