泽西岛SSE-发送第一条消息后，eventOutput.write会引发nullpointer [英] Jersey SSE - eventOutput.write throws nullpointer after first message is sent
问题描述
我已经使用Jersey实现了Restful Web界面，用于通过HTTP将从内部JMS发布者接收到的消息发送到外部客户端.我设法将测试消息发送给Java客户端，但是Thread在完成write()执行，关闭连接并阻止进一步通信之前引发了空指针异常.
I have implemented a Restful web interface using Jersey for sending messages received from an internal JMS publisher to external clients via HTTP. I have managed to get a test message out to a Java client, but the Thread throws a null pointer exception before completing the write() execution, closing the connection and preventing further communication.
这是我的资源分类:
@GET
@Path("/stream_data")
@Produces(SseFeature.SERVER_SENT_EVENTS)
public EventOutput getServerSentEvents(@Context ServletContext context){
final EventOutput eventOutput = new EventOutput();
new Thread( new ObserverThread(eventOutput, (MService) context.getAttribute("instance")) ).start();
return eventOutput;
}
这是我线程的运行方法:
And here is my thread's run method:
public class ObserverThread implements Observer, Runnable {
//constructor sets eventOutput & mService objects
//mService notifyObservers() called when JMS message received
//text added to Thread's message queue to await sending to client
public void run() {
try {
String message = "{'symbol':'test','entryType'='0','price'='test'}";
Thread.sleep(1000);
OutboundEvent.Builder builder = new OutboundEvent.Builder();
builder.mediaType(MediaType.APPLICATION_JSON_TYPE);
builder.data(String.class, message);
OutboundEvent event = builder.build();
eventOutput.write(event);
System.out.println(">>>>>>SSE CLIENT HAS BEEN REGISTERED!");
mService.addObserver(this);
while(!eventOutput.isClosed()){
if(!updatesQ.isEmpty()){
pushUpdate(updatesQ.dequeue());
}
}
System.out.println("<<<<<<<SSE CLIENT HAS BEEN DEREGISTERED!");
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
这是我的客户代码:
Client client = ClientBuilder.newBuilder().register(SseFeature.class).build();
WebTarget target = client.target(url);
EventInput eventInput = target.request().get(EventInput.class);
try {
while (!eventInput.isClosed()) {
eventInput.setChunkType(MediaType.WILDCARD_TYPE);
final InboundEvent inboundEvent = eventInput.read();
if (inboundEvent != null) {
String theString = inboundEvent.readData();
System.out.println(theString + "\n");
}
}
} catch (Exception e) {
e.printStackTrace();
}
我正在将"{'symbol':'test'，'entryType'='0'，'price'='test'}"测试消息打印到客户端控制台，但是服务器随后会在之前打印NullPointerException它可以打印">>>> SSE Client已注册"消息.这将关闭连接，因此客户端退出while循环并停止侦听更新.
I am getting the "{'symbol':'test','entryType'='0','price'='test'}" test message printed to the client console, but the server then prints a NullPointerException before it can print the ">>>>SSE Client registered" message. This closes the connection so the client exits the while loop and stops listening for updates.
我将项目转换为webapp 3.0版本，以便将异步支持的标签添加到web.xml，但是我收到相同的空指针错误.我倾向于认为这是由于Servlet在返回第一条消息后终止了Request/Response对象而引起的，证据显示在堆栈跟踪中:
I converted the project to a webapp 3.0 version facet in order to add an async-supported tag to the web.xml but i am receiving the same null pointer error. I am inclined to think that it is caused by the servlet ending the Request/Response objects once the first message is returned, evidence is shown in the stack trace:
Exception in thread "Thread-20" java.lang.NullPointerException
at org.apache.coyote.http11.InternalOutputBuffer.realWriteBytes(InternalOutputBuffer.java:741)
at org.apache.tomcat.util.buf.ByteChunk.flushBuffer(ByteChunk.java:434)
at org.apache.coyote.http11.InternalOutputBuffer.flush(InternalOutputBuffer.java:299)
at org.apache.coyote.http11.Http11Processor.action(Http11Processor.java:981)
at org.apache.coyote.Response.action(Response.java:183)
at org.apache.catalina.connector.OutputBuffer.doFlush(OutputBuffer.java:314)
at org.apache.catalina.connector.OutputBuffer.flush(OutputBuffer.java:288)
at org.apache.catalina.connector.CoyoteOutputStream.flush(CoyoteOutputStream.java:98)
at org.glassfish.jersey.message.internal.CommittingOutputStream.flush(CommittingOutputStream.java:292)
at org.glassfish.jersey.server.ChunkedOutput$1.call(ChunkedOutput.java:241)
at org.glassfish.jersey.server.ChunkedOutput$1.call(ChunkedOutput.java:192)
at org.glassfish.jersey.internal.Errors.process(Errors.java:315)
at org.glassfish.jersey.internal.Errors.process(Errors.java:242)
at org.glassfish.jersey.process.internal.RequestScope.runInScope(RequestScope.java:345)
at org.glassfish.jersey.server.ChunkedOutput.flushQueue(ChunkedOutput.java:192)
at org.glassfish.jersey.server.ChunkedOutput.write(ChunkedOutput.java:182)
at com.bpc.services.service.ObserverThread.run(MarketObserverThread.java:32)
at java.lang.Thread.run(Thread.java:745)
<<<<<<<SSE CLIENT HAS BEEN DEREGISTERED!
我也尝试过测试sse广播器.在这种情况下，我看不到任何异常，但是一旦收到第一条消息，连接就会关闭，这使我相信这是Servlet中的某种事情，它迫使连接关闭.谁能建议我如何在服务器端进行调试?
I have attempted to test an sse broadcaster as well. In this case I am not seeing any exceptions thrown, but the connection is closed once the first message has been received, leading me to believe it is something in the servlet forcing the connection to close. Can anyone advise me on how to debug this on the server-side?
推荐答案
我在Jersey对ExecutorService实例的@Context注入中似乎存在一个长期存在的错误，也遇到了类似的问题.在当前的Sse(版本2.27)中，
I had a similar issue from what seems to be a long standing bug in Jersey's @Context injection for ExecutorService instances. In their current implementation of Sse (version 2.27),
class JerseySse implements Sse {
@Context
private ExecutorService executorService;
@Override
public OutboundSseEvent.Builder newEventBuilder() {
return new OutboundEvent.Builder();
}
@Override
public SseBroadcaster newBroadcaster() {
return new JerseySseBroadcaster(executorService);
}
}
executorService字段从未初始化，因此在我的情况下，JerseySseBroadcaster会引发NullPointerException.我通过显式触发注入来解决该错误.
the executorService field is never initialized, so the JerseySseBroadcaster raises a NullPointerException in my case. I worked around the bug by explicitly triggering the injection.
如果您使用HK2进行CDI(Jersey的默认设置)，则上述问题的解决方案概图可能类似于以下内容:
If you're using HK2 for CDI (Jersey's default), a rough sketch of a solution to the question above could look similar to the following:
@Singleton
@Path("...")
public class JmsPublisher {
private Sse sse;
private SseBroadcaster broadcaster;
private final ExecutorService executor;
private final BlockingQueue<String> jmsMessageQueue;
...
@Context
public void setSse(Sse sse, ServiceLocator locator) {
locator.inject(sse); // Inject sse.executorService
this.sse = sse;
this.broadcaster = sse.newBroadcaster();
}
...
@GET
@Path("/stream_data")
@Produces(MediaType.SERVER_SENT_EVENTS)
public void register(SseEventSink eventSink) {
broadcaster.register(eventSink);
}
...
@PostConstruct
private void postConstruct() {
executor.submit(() -> {
try {
while(true) {
String message = jmsMessageQueue.take();
broadcaster.broadcast(sse.newEventBuilder()
.mediaType(MediaType.APPLICATION_JSON_TYPE)
.data(String.class, message)
.build());
}
} catch(InterruptedException e) {
Thread.currentThread().interrupt();
}
});
}
@PreDestroy
private void preDestroy() {
executor.shutdownNow();
}
}
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