Servlet-Tomcat如何关闭response的outputStream

布满荆棘的人生 2021-06-22 15:36 652阅读 0赞

## **序** ##

在写文件下载的时候，遇到了一个问题，就是这个ServletOutputStream到底要不要自己flush以及close。这里以tomcat容易为例，解读一下。

## **CoyoteAdapter** ##

tomcat-embed-core-8.5.16-sources.jar!/org/apache/catalina/connector/CoyoteAdapter.java 主要看service这段代码：

@Override
        public void service(org.apache.coyote.Request req, org.apache.coyote.Response res)
                throws Exception {
    
            Request request = (Request) req.getNote(ADAPTER_NOTES);
            Response response = (Response) res.getNote(ADAPTER_NOTES);
    
            if (request == null) {
                // Create objects
                request = connector.createRequest();
                request.setCoyoteRequest(req);
                response = connector.createResponse();
                response.setCoyoteResponse(res);
    
                // Link objects
                request.setResponse(response);
                response.setRequest(request);
    
                // Set as notes
                req.setNote(ADAPTER_NOTES, request);
                res.setNote(ADAPTER_NOTES, response);
    
                // Set query string encoding
                req.getParameters().setQueryStringCharset(connector.getURICharset());
            }
    
            if (connector.getXpoweredBy()) {
                response.addHeader("X-Powered-By", POWERED_BY);
            }
    
            boolean async = false;
            boolean postParseSuccess = false;
    
            req.getRequestProcessor().setWorkerThreadName(THREAD_NAME.get());
    
            try {
                // Parse and set Catalina and configuration specific
                // request parameters
                postParseSuccess = postParseRequest(req, request, res, response);
                if (postParseSuccess) {
                    //check valves if we support async
                    request.setAsyncSupported(
                            connector.getService().getContainer().getPipeline().isAsyncSupported());
                    // Calling the container
                    // 这里调用具体的servlet方法，使用springmvc的话，就是调用mvc的方法
                    connector.getService().getContainer().getPipeline().getFirst().invoke(
                            request, response);
                }
                if (request.isAsync()) {
                    async = true;
                    ReadListener readListener = req.getReadListener();
                    if (readListener != null && request.isFinished()) {
                        // Possible the all data may have been read during service()
                        // method so this needs to be checked here
                        ClassLoader oldCL = null;
                        try {
                            oldCL = request.getContext().bind(false, null);
                            if (req.sendAllDataReadEvent()) {
                                req.getReadListener().onAllDataRead();
                            }
                        } finally {
                            request.getContext().unbind(false, oldCL);
                        }
                    }
    
                    Throwable throwable =
                            (Throwable) request.getAttribute(RequestDispatcher.ERROR_EXCEPTION);
    
                    // If an async request was started, is not going to end once
                    // this container thread finishes and an error occurred, trigger
                    // the async error process
                    if (!request.isAsyncCompleting() && throwable != null) {
                        request.getAsyncContextInternal().setErrorState(throwable, true);
                    }
                } else {
                    request.finishRequest();
                    //这里去关闭response
                    response.finishResponse();
                }
    
            } catch (IOException e) {
                // Ignore
            } finally {
                AtomicBoolean error = new AtomicBoolean(false);
                res.action(ActionCode.IS_ERROR, error);
    
                if (request.isAsyncCompleting() && error.get()) {
                    // Connection will be forcibly closed which will prevent
                    // completion happening at the usual point. Need to trigger
                    // call to onComplete() here.
                    res.action(ActionCode.ASYNC_POST_PROCESS,  null);
                    async = false;
                }
    
                // Access log
                if (!async && postParseSuccess) {
                    // Log only if processing was invoked.
                    // If postParseRequest() failed, it has already logged it.
                    Context context = request.getContext();
                    // If the context is null, it is likely that the endpoint was
                    // shutdown, this connection closed and the request recycled in
                    // a different thread. That thread will have updated the access
                    // log so it is OK not to update the access log here in that
                    // case.
                    if (context != null) {
                        context.logAccess(request, response,
                                System.currentTimeMillis() - req.getStartTime(), false);
                    }
                }
    
                req.getRequestProcessor().setWorkerThreadName(null);
    
                // Recycle the wrapper request and response
                if (!async) {
                    request.recycle();
                    response.recycle();
                }
            }
        }

## **Response.finishResponse** ##

tomcat-embed-core-8.5.16-sources.jar!/org/apache/catalina/connector/Response.java

public class Response implements HttpServletResponse {
        //......
        /**
         * The associated output buffer.
         */
        protected OutputBuffer outputBuffer;
    
        /**
         * The associated output stream.
         */
        protected CoyoteOutputStream outputStream;
       //......
       /**
         * Perform whatever actions are required to flush and close the output
         * stream or writer, in a single operation.
         *
         * @exception IOException if an input/output error occurs
         */
        public void finishResponse() throws IOException {
            // Writing leftover bytes
            outputBuffer.close();
        }
    
    }

## **OutputBuffer.close** ##

tomcat-embed-core-8.5.16-sources.jar!/org/apache/catalina/connector/OutputBuffer.java

/**
         * Close the output buffer. This tries to calculate the response size if
         * the response has not been committed yet.
         *
         * @throws IOException An underlying IOException occurred
         */
        @Override
        public void close() throws IOException {
    
            if (closed) {
                return;
            }
            if (suspended) {
                return;
            }
    
            // If there are chars, flush all of them to the byte buffer now as bytes are used to
            // calculate the content-length (if everything fits into the byte buffer, of course).
            if (cb.remaining() > 0) {
                flushCharBuffer();
            }
    
            if ((!coyoteResponse.isCommitted()) && (coyoteResponse.getContentLengthLong() == -1)
                    && !coyoteResponse.getRequest().method().equals("HEAD")) {
                // If this didn't cause a commit of the response, the final content
                // length can be calculated. Only do this if this is not a HEAD
                // request since in that case no body should have been written and
                // setting a value of zero here will result in an explicit content
                // length of zero being set on the response.
                if (!coyoteResponse.isCommitted()) {
                    coyoteResponse.setContentLength(bb.remaining());
                }
            }
    
            if (coyoteResponse.getStatus() == HttpServletResponse.SC_SWITCHING_PROTOCOLS) {
                doFlush(true);
            } else {
                doFlush(false);
            }
            closed = true;
    
            // The request should have been completely read by the time the response
            // is closed. Further reads of the input a) are pointless and b) really
            // confuse AJP (bug 50189) so close the input buffer to prevent them.
            Request req = (Request) coyoteResponse.getRequest().getNote(CoyoteAdapter.ADAPTER_NOTES);
            req.inputBuffer.close();
    
            coyoteResponse.action(ActionCode.CLOSE, null);
        }

> 这里flush了一下

private void flushCharBuffer() throws IOException {
            realWriteChars(cb.slice());
            clear(cb);
        }
    
        /**
         * Flush bytes or chars contained in the buffer.
         *
         * @param realFlush <code>true</code> if this should also cause a real network flush
         * @throws IOException An underlying IOException occurred
         */
        protected void doFlush(boolean realFlush) throws IOException {
    
            if (suspended) {
                return;
            }
    
            try {
                doFlush = true;
                if (initial) {
                    coyoteResponse.sendHeaders();
                    initial = false;
                }
                if (cb.remaining() > 0) {
                    flushCharBuffer();
                }
                if (bb.remaining() > 0) {
                    flushByteBuffer();
                }
            } finally {
                doFlush = false;
            }
    
            if (realFlush) {
                coyoteResponse.action(ActionCode.CLIENT_FLUSH, null);
                // If some exception occurred earlier, or if some IOE occurred
                // here, notify the servlet with an IOE
                if (coyoteResponse.isExceptionPresent()) {
                    throw new ClientAbortException(coyoteResponse.getErrorException());
                }
            }
    
        }

这个正好印证了servlet3.1规范里头说的(`5.6 Closure of Response Object`)

> When a response is closed, the container must immediately flush all remaining content in the response buffer to the client.

## **Response.getOutputStream** ##

/**
         * @return the servlet output stream associated with this Response.
         *
         * @exception IllegalStateException if <code>getWriter</code> has
         *  already been called for this response
         * @exception IOException if an input/output error occurs
         */
        @Override
        public ServletOutputStream getOutputStream()
            throws IOException {
    
            if (usingWriter) {
                throw new IllegalStateException
                    (sm.getString("coyoteResponse.getOutputStream.ise"));
            }
    
            usingOutputStream = true;
            if (outputStream == null) {
                outputStream = new CoyoteOutputStream(outputBuffer);
            }
            return outputStream;
    
        }

### **CoyoteOutputStream的flush和close方法** ###

tomcat-embed-core-8.5.16-sources.jar!/org/apache/catalina/connector/CoyoteOutputStream.java

/**
         * Will send the buffer to the client.
         */
        @Override
        public void flush() throws IOException {
            boolean nonBlocking = checkNonBlockingWrite();
            ob.flush();
            if (nonBlocking) {
                checkRegisterForWrite();
            }
        }
      
    @Override
        public void close() throws IOException {
            ob.close();
        }

> 也都是调用OutputBuffer的flush和close方法。因此手工调用貌似没有必要。

## **doc** ##

*  servlet-3\_1-fr-eval-spec
 *  Response.getWriter() should it be closed / flushed
 *  Do I need to flush the servlet outputstream?