我知道在EJB里面搞线程是大忌,但我想请教一下如何处理这个案例。我的EJB正在调用一个外部的Web服务,这个服务有时会返回一个 "繁忙 "状态。当这种情况发生时,我希望等待一段时间,然后使用与之前相同的数据重新提交请求。
实现这个问题的最好方法是什么?
EJB 3.1带来了一个新的 @Asynchronous
特征 你可以利用的。
@Asynchronous
@TransactionAttribute(NOT_SUPPORTED)
public Future<WebServiceResult> callWebService(int retries) {
WebServiceResult result = webService.call();
if (!result.equals(BUSY)) {
return result;
}
if (retries <= 0) {
throw new TooBusyException();
}
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
}
return callWebService(retries - 1);
}
然后简单地调用你的网络服务,
Future<WebServiceResult> result = yourEJB.callWebService(1);
// Can do some interesting stuff here.
// ...
// ...
result.get(2, SECONDS); // Block for up to 2 seconds.
如你所见,你可以免费获得可配置的重试次数和超时次数。
这与仅仅调用 Thread.sleep()
? 返回 Future
是比较明确和容易管理的。另外,我不认为 Thread.sleep()
是那么的有害。唯一的问题是,现在这个EJB实例不能再被其他客户重用了。有了 Future
异步调用发生在其他EJB和线程池内。至于 Thread#interrupt()
挡板内,请参考 为什么在捕捉任何InterruptException时要调用Thread.currentThread.interrupt()?
另一个想法:在调用web服务时使用方面,捕捉 BusyException
一次,然后重试。
但是外部的web服务是外部的,你要给它开通网络连接,你希望做一些管理的事情。 这就是JCA的作用,而不是EJB。
这里有一个建议(或者说是另一种方法),用简单控件的池子。
1 - 把你的上下文(EJB)作为参数传给你的方法(rest endpoint, scheduler, default's methods)
2-用互补的调度器或实体标志来控制状态。
3 - 小心数据处理的数量
4-建议。强烈建议指标、日志和测试、试验、测试。
5 - 这段代码是在SpringBoot上,但在Jboss中进行了测试(经过修改),在EJB上下文下--仔细测试。
6-根据您的意愿进行修改。(发送建议-评论)
BaseControlExecutor.java
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;
import java.util.concurrent.ScheduledThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
public class BaseControlExecutor {
private final ScheduledThreadPoolExecutor poolExec = new ScheduledThreadPoolExecutor(2);
public void execWithTimeout(final Runnable runnable, long timeout,
TimeUnit timeUnit) throws Exception {
execWithTimeout(new Callable<Object>() {
@Override
public Object call() throws Exception {
runnable.run();
return null;
}
}, timeout, timeUnit);
}
public <T> T execWithTimeout(Callable<T> callable, long timeout, TimeUnit timeUnit) throws Exception {
final Future<T> future = poolExec.submit(callable);
try {
return future.get(timeout, timeUnit);
} catch (TimeoutException e) {
future.cancel(true);
throw e;
} catch (ExecutionException e) {
Throwable t = e.getCause();
if (t instanceof Error) {
throw (Error) t;
} else if (t instanceof Exception) {
throw (Exception) t;
} else {
throw new IllegalStateException(t);
}
}
}
}
EndpointControlRest.java
import java.time.Duration;
import java.time.Instant;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
import java.util.concurrent.atomic.AtomicLong;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import io.swagger.annotations.Api;
import io.swagger.annotations.ApiOperation;
@RestController
@RequestMapping(value = "/report")
@Api(tags = "Endpoint of Future")
public class EndpointControlRest extends BaseControlExecutor {
Logger logger = LoggerFactory.getLogger(EndpointControlRest.class);
//single metric of execution
protected final AtomicLong counter = new AtomicLong();
@GetMapping(path = "/withThread", produces = { "application/json" })
@ApiOperation(value = "Return Hello count.")
public String greeting() {
Long countRunner = counter.incrementAndGet();
String json = ""; //or EJB context to use in Thread - becareful
new Thread(() -> {
try {
execWithTimeout(new Runnable() {
@Override
public void run() {
Instant start = Instant.now();
logger.info("Report init - " + countRunner);
//generating reports
generateBackgroundReport(json);
logger.info("Report End - " + countRunner);
Instant finish = Instant.now();
long timeElapsed = Duration.between(start, finish).toMillis();
logger.info("###DEBUG - " + countRunner + " - OK |Time exe: " + timeElapsed);
}
}, 120, TimeUnit.SECONDS);
} catch (TimeoutException e) {
logger.info("###DEBUG - " + countRunner + " - Timeout - " + e.getMessage());
} catch (Exception e) {
logger.info("###DEBUG - " + countRunner + " - Exception - " + e.getMessage());
}
}).start();
logger.info("####DEBUG - Rest call released");
return "Hello " + countRunner;
}
public String generateBackgroundReport(String json){
//simulating work
Long x = 0L;
for(Long i = 0L; i < 1000000000L; i ++){
x = i + 1;
}
logger.info("####DEBUG -report: " + x);
return "OK";
}
}