Servlet 处理 applet 通信和 http 请求答案

【问题标题】：Servlet to handle both applet communication and http requestsServlet 处理 applet 通信和 http 请求
【发布时间】：2010-10-18 12:17:02
【问题描述】：

我正在构建一个解决方案，其中tomcat6 上的servlet 通过提供一个jsp 网页来处理来自另一台机器的输入。我还希望同一个 servlet 与同一台机器上的小程序通信，以显示一些结果并执行一些任务。

我可以使用 URLConnection 从小程序连接到 servlet，但是当从 servlet 接收消息时，我从小程序收到“无效的流标头”异常消息。

有什么想法吗？

编辑：错误信息：

java.io.StreamCorruptedException: invalid stream header: 0A0A0A3C at java.io.ObjectInputStream.readStreamHeader(ObjectInputStream.java:783) at java.io.ObjectInputStream.<init>(ObjectInputStream.java:280) at applet.viewApplet.onSendData(viewApplet.java:126)

小程序代码：

 private URLConnection getServletConnection()
        throws MalformedURLException, IOException {

    // Open the servlet connection
    URL urlServlet = new URL("http://localhost:8080/Servlet");
    connection = urlServlet.openConnection();

    // Config
    connection.setDoInput(true);
    connection.setDoOutput(true);

    connection.setUseCaches (false);
    connection.setDefaultUseCaches (false);

    connection.setRequestProperty(
            "Content-Type",
            "application/x-java-serialized-object");

    return connection;
}

private void onSendData() {
    try {
        // get input data for sending
        String input = "Applet string heading for servlet";

        // send data to the servlet
        connection = getServletConnection();
        OutputStream outstream = connection.getOutputStream();
        ObjectOutputStream oos = new ObjectOutputStream(outstream);
        oos.writeObject(input);
        oos.flush();
        oos.close()

        // receive result from servlet
        InputStream instr = connection.getInputStream();
        ObjectInputStream inputFromServlet = new ObjectInputStream(instr);
        String result = (String) inputFromServlet.readObject();
        inputFromServlet.close();
        instr.close();

        // show result
        textField.setText(result);

    } catch (java.net.MalformedURLException mue) {
        textField.setText("Invalid serlvetUrl, error: " + mue.getMessage());
    } catch (java.io.IOException ioe) {
        textField.setText("Couldn't open a URLConnection, error: " + ioe.getMessage());
    } catch (Exception e) {
        textField.setText("Exception caught, error: " + e.getMessage());
    }
}

Servlet 代码：

public class Servlet extends HttpServlet {

protected void processRequest(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    response.setContentType("text/html;charset=ISO-8859-1");
    PrintWriter out = response.getWriter();
    String defect = request.getParameter("defect").toString();

    try {
        out.println("<html>");
        out.println("<head>");
        out.println("<title>Servlet</title>");
        out.println("</head>");
        out.println("<body>");
        out.println("<h1>Servlet at " + request.getContextPath() + "</h1>");
        out.println("<p>Defect: " + defect + "</p>");
        out.println("</body>");
        out.println("</html>");
    } finally {
        out.close();
    }
}

@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    processRequest(request, response);
}

@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {

    try {
        response.setContentType("application/x-java-serialized-object");

        InputStream in = request.getInputStream();
        ObjectInputStream inputFromApplet = new ObjectInputStream(in);

        String servletText = "Text from Servlet";

        // echo it to the applet
        OutputStream outstr = response.getOutputStream();
        ObjectOutputStream oos = new ObjectOutputStream(outstr);
        oos.writeObject(servletText);
        oos.flush();
        oos.close();

    } catch (Exception e) {
        e.printStackTrace();
    }

    processRequest(request, response);
}

【问题讨论】：

看起来你处理 POST(doPost) 的 servlet 应该处理一个序列化的对象，而你的 URLConnection 将发送一个 get （并最终在 doGet 中） - 或者是故意的？

标签： java servlets applet stream urlconnection

【解决方案1】：

这是因为您尝试使用 ObjectInputStream 反序列化 servlet 的基于文本的响应主体，而它根本没有被序列化，您应该为此使用 Reader。

长话短说：How to fire and handle HTTP requests using URLConnection?。

【讨论】：