java - HttpComponents 如何发送响应？

Question

我正在尝试学习如何使用 Apache HttpComponents 发送 HttpResponse。我发现some examples在 Apache 网站上，但它们非常困惑且不清楚。

在下面的代码中，我看不到 HttpResponse 是在哪里生成并发送回客户端的。跟踪代码后，似乎它一定发生在 HttpFileHandler 类的handle() 方法中，但不清楚在哪里。类(class)以

结束

...
response.setEntity(body);
System.out.println("File " + file.getPath() + " not found");
...

没有实际发送响应。最后以设置实体结束。

在此代码中，将响应发送回客户端实际上发生在哪里？

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package org.apache.http.examples;

import java.io.File;
import java.io.IOException;
import java.io.InterruptedIOException;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.net.ServerSocket;
import java.net.Socket;
import java.net.URLDecoder;
import java.util.Locale;

import org.apache.http.ConnectionClosedException;
import org.apache.http.HttpEntity;
import org.apache.http.HttpEntityEnclosingRequest;
import org.apache.http.HttpException;
import org.apache.http.HttpRequest;
import org.apache.http.HttpResponse;
import org.apache.http.HttpResponseInterceptor;
import org.apache.http.HttpServerConnection;
import org.apache.http.HttpStatus;
import org.apache.http.MethodNotSupportedException;
import org.apache.http.entity.ContentProducer;
import org.apache.http.entity.EntityTemplate;
import org.apache.http.entity.FileEntity;
import org.apache.http.impl.DefaultConnectionReuseStrategy;
import org.apache.http.impl.DefaultHttpResponseFactory;
import org.apache.http.impl.DefaultHttpServerConnection;
import org.apache.http.params.CoreConnectionPNames;
import org.apache.http.params.CoreProtocolPNames;
import org.apache.http.params.HttpParams;
import org.apache.http.params.SyncBasicHttpParams;
import org.apache.http.protocol.BasicHttpContext;
import org.apache.http.protocol.HttpContext;
import org.apache.http.protocol.HttpProcessor;
import org.apache.http.protocol.HttpRequestHandler;
import org.apache.http.protocol.HttpRequestHandlerRegistry;
import org.apache.http.protocol.HttpService;
import org.apache.http.protocol.ImmutableHttpProcessor;
import org.apache.http.protocol.ResponseConnControl;
import org.apache.http.protocol.ResponseContent;
import org.apache.http.protocol.ResponseDate;
import org.apache.http.protocol.ResponseServer;
import org.apache.http.util.EntityUtils;

/**
 * Basic, yet fully functional and spec compliant, HTTP/1.1 file server.
 * <p>
 * Please note the purpose of this application is demonstrate the usage of
 * HttpCore APIs. It is NOT intended to demonstrate the most efficient way of
 * building an HTTP file server.
 * 
 * 
 */
public class ElementalHttpServer {

    public static void main(String[] args) throws Exception {
        args = new String[] { "e:/tutoring/236369/Tutorials/httpCoreExamples/" };
        if (args.length < 1) {
            System.err.println("Please specify document root directory");
            System.exit(1);
        }
        Thread t = new RequestListenerThread(8080, args[0]);
        t.setDaemon(false);
        t.start();
    }

    static class HttpFileHandler implements HttpRequestHandler {

        private final String docRoot;

        public HttpFileHandler(final String docRoot) {
            super();
            this.docRoot = docRoot;
        }

        @Override
        public void handle(final HttpRequest request,
                final HttpResponse response, final HttpContext context)
                throws HttpException, IOException {

            String method = request.getRequestLine().getMethod()
                    .toUpperCase(Locale.ENGLISH);
            if (!method.equals("GET") && !method.equals("HEAD")
                    && !method.equals("POST")) {
                throw new MethodNotSupportedException(method
                        + " method not supported");
            }
            String target = request.getRequestLine().getUri();

            if (request instanceof HttpEntityEnclosingRequest) {
                HttpEntity entity = ((HttpEntityEnclosingRequest) request)
                        .getEntity();
                byte[] entityContent = EntityUtils.toByteArray(entity);
                System.out.println("Incoming entity content (bytes): "
                        + entityContent.length);
            }

            final File file = new File(this.docRoot, URLDecoder.decode(target));
            if (!file.exists()) {

                response.setStatusCode(HttpStatus.SC_NOT_FOUND);
                EntityTemplate body = new EntityTemplate(new ContentProducer() {

                    @Override
                    public void writeTo(final OutputStream outstream)
                            throws IOException {
                        OutputStreamWriter writer = new OutputStreamWriter(
                                outstream, "UTF-8");
                        writer.write("<html><body><h1>");
                        writer.write("File ");
                        writer.write(file.getPath());
                        writer.write(" not found");
                        writer.write("</h1></body></html>");
                        writer.flush();
                    }

                });
                body.setContentType("text/html; charset=UTF-8");
                response.setEntity(body);
                System.out.println("File " + file.getPath() + " not found");

            } else if (!file.canRead() || file.isDirectory()) {

                response.setStatusCode(HttpStatus.SC_FORBIDDEN);
                EntityTemplate body = new EntityTemplate(new ContentProducer() {

                    @Override
                    public void writeTo(final OutputStream outstream)
                            throws IOException {
                        OutputStreamWriter writer = new OutputStreamWriter(
                                outstream, "UTF-8");
                        writer.write("<html><body><h1>");
                        writer.write("Access denied");
                        writer.write("</h1></body></html>");
                        writer.flush();
                    }

                });
                body.setContentType("text/html; charset=UTF-8");
                response.setEntity(body);
                System.out.println("Cannot read file " + file.getPath());

            } else {

                response.setStatusCode(HttpStatus.SC_OK);
                FileEntity body = new FileEntity(file, "text/html");
                response.setEntity(body);
                System.out.println("Serving file " + file.getPath());

            }
        }

    }

    static class RequestListenerThread extends Thread {

        private final ServerSocket serversocket;
        private final HttpParams params;
        private final HttpService httpService;

        public RequestListenerThread(int port, final String docroot)
                throws IOException {
            this.serversocket = new ServerSocket(port);
            this.params = new SyncBasicHttpParams();
            this.params
                    .setIntParameter(CoreConnectionPNames.SO_TIMEOUT, 5000)
                    .setIntParameter(CoreConnectionPNames.SOCKET_BUFFER_SIZE,
                            8 * 1024)
                    .setBooleanParameter(
                            CoreConnectionPNames.STALE_CONNECTION_CHECK, false)
                    .setBooleanParameter(CoreConnectionPNames.TCP_NODELAY, true)
                    .setParameter(CoreProtocolPNames.ORIGIN_SERVER,
                            "HttpComponents/1.1");

            // Set up the HTTP protocol processor
            HttpProcessor httpproc = new ImmutableHttpProcessor(
                    new HttpResponseInterceptor[] { new ResponseDate(),
                            new ResponseServer(), new ResponseContent(),
                            new ResponseConnControl() });

            // Set up request handlers
            HttpRequestHandlerRegistry reqistry = new HttpRequestHandlerRegistry();
            reqistry.register("*", new HttpFileHandler(docroot));

            // Set up the HTTP service
            this.httpService = new HttpService(httpproc,
                    new DefaultConnectionReuseStrategy(),
                    new DefaultHttpResponseFactory(), reqistry, this.params);
        }

        @Override
        public void run() {
            System.out.println("Listening on port "
                    + this.serversocket.getLocalPort());
            while (!Thread.interrupted()) {
                try {
                    // Set up HTTP connection
                    Socket socket = this.serversocket.accept();
                    DefaultHttpServerConnection conn = new DefaultHttpServerConnection();
                    System.out.println("Incoming connection from "
                            + socket.getInetAddress());
                    conn.bind(socket, this.params);

                    // Start worker thread
                    Thread t = new WorkerThread(this.httpService, conn);
                    t.setDaemon(true);
                    t.start();
                } catch (InterruptedIOException ex) {
                    break;
                } catch (IOException e) {
                    System.err
                            .println("I/O error initialising connection thread: "
                                    + e.getMessage());
                    break;
                }
            }
        }
    }

    static class WorkerThread extends Thread {

        private final HttpService httpservice;
        private final HttpServerConnection conn;

        public WorkerThread(final HttpService httpservice,
                final HttpServerConnection conn) {
            super();
            this.httpservice = httpservice;
            this.conn = conn;
        }

        @Override
        public void run() {
            System.out.println("New connection thread");
            HttpContext context = new BasicHttpContext(null);
            try {
                while (!Thread.interrupted() && this.conn.isOpen()) {
                    this.httpservice.handleRequest(this.conn, context);
                }
            } catch (ConnectionClosedException ex) {
                System.err.println("Client closed connection");
            } catch (IOException ex) {
                System.err.println("I/O error: " + ex.getMessage());
            } catch (HttpException ex) {
                System.err.println("Unrecoverable HTTP protocol violation: "
                        + ex.getMessage());
            } finally {
                try {
                    this.conn.shutdown();
                } catch (IOException ignore) {
                }
            }
        }

    }

}

Answer 1

您正在此处运行服务器。

库已经实现了“谈论 HTTP”的通用代码。

您只需插入“业务逻辑”(以 HTTPRequestHandler 的形式)。

您的“业务逻辑”获取 HTTPResponse 的实例作为参数。该对象已由图书馆为您创建。您可以设置参数并写入数据。

当您的处理程序方法返回时(或者甚至在您操作响应对象之前)，该库负责通过网络获取数据。

Where does the sending of the response back to the client actually happen in this code?

作为方法handle的结果，响应对象现在包含一个具有内部类的实体，可以写出文件。该代码将被调用来发送数据。

在代码中放置断点并单步执行(包括句柄返回后的部分)以查看控制流可能会很有启发性(或者可能令人难以接受)。