Ajax PUT 请求接收空响应

Question

我已经编写了一个 HttpCRUDServlet，它将执行以下任务（到目前为止）。

• 使用适当的 CORS 标头 (service()) 响应 OPTIONS 方法，
• 将 PUT 请求中传递的数据解析并插入到数据库 (doPut())。

所有功能似乎都运行良好，除了客户端收到空响应。

来源：

package com.gamersdemokrasy.http;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;
import java.net.URLDecoder;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.json.JSONException;
import org.json.JSONObject;

import com.gamersdemokrasy.DAO;
import com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException;

/**
 * Servlet implementation class HttpCRUDServlet
 */
public class HttpCRUDServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
private String uri = null;

/**
 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
 */
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    // TODO Auto-generated method stub
}

/**
 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
 */
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    // TODO Auto-generated method stub
}

/*
 * @see HttpServlet#doDelete(HttpServletRequest, HttpServletResponse)
 */
@Override
protected void doDelete(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    // TODO Auto-generated method stub
    super.doDelete(request, response);
}

/*
 * @see HttpServlet#doPut(HttpServletRequest, HttpServletResponse)
 */
@Override
protected void doPut(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    JSONObject dataJson = getJsonData(new BufferedReader(new InputStreamReader(request.getInputStream())).readLine());

    response.getWriter().println("Hello");
    DAO dao = new DAO();
    try {
        if(dao.create(dataJson, uri)) {
            response.setStatus(HttpServletResponse.SC_OK);
        } else if(dao.getException() instanceof MySQLIntegrityConstraintViolationException) {
            response.setContentType("text/plain");
            response.getWriter().println(dao.getException().getMessage());
            response.setStatus(HttpServletResponse.SC_CONFLICT);
            dao.getException().printStackTrace();
        } else if(dao.getException() instanceof Exception) {
            response.setContentType("text/plain");
            response.getWriter().println(dao.getException().getMessage());
            response.setStatus(HttpServletResponse.SC_INTERNAL_SERVER_ERROR);
            dao.getException().printStackTrace();
        }
    } finally {
        response.getWriter().flush();
        response.getWriter().close();
    }

}

/**
 * Converts a parameter string into a JSONObject
 * 
 * @param data
 * @return
 */
private JSONObject getJsonData(String data) {
    JSONObject json = new JSONObject();

    String[] params = data.split("&");
    try {
        for(String param:params) {
            String tokens[] = param.split("=");
            json.accumulate(URLDecoder.decode(tokens[0].trim(),"utf-8"), URLDecoder.decode(tokens[1].trim(),"utf-8"));
        }
    } catch (JSONException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (UnsupportedEncodingException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

    return json;
}

/*
 * @see HttpServlet#service(HttpServletRequest, HttpServletResponse)
 */
@Override
protected void service(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    String method = request.getMethod();
    uri = request.getRequestURI().replaceFirst(request.getContextPath(), "");
    while(uri.endsWith("/")) {
        uri = uri.substring(0, uri.length()-1);
    }
    System.out.println("Debug>> Request:"+method + " " + uri);
    System.out.println("Debug>> ContextPath:"+request.getContextPath());

    if(request.getMethod().equals("OPTIONS")) {
        // Set CORS headers
        response.setHeader("Access-Control-Allow-Origin", "*");
        response.setHeader("Access-Control-Allow-Methods",
                "PUT,GET,POST,DELETE");
        response.setHeader("Allow", "PUT,GET,POST,DELETE");
        response.setHeader("Access-Control-Max-Age", "180");
        response.setHeader("Access-Control-Allow-Headers", "Content-type");
    } else if(method.equals("PUT") || method.equals("GET")
            || method.equals("POST") || method.equals("DELETE")) {
        super.service(request, response);
    }
}

}

这里是 ajax 代码：

    $.ajax({
        url: 'http://localhost:8080/gamedem/user/',
        type: 'PUT',
        data: {
            id: 'dominick',
            nick: 'pr@da.n4m3s!s',
            phno: '9739097300',
            steam_id: 'lorddominique',
            games_played: 'cs1.6'
            //phno1: 9999999999
        },
        //contentType: 'text/plain',
        contentType: 'application/json',
        success: function() {
            alert("Resource Created");
        }
    });

我在 iceweasel 3.5.16 上使用 Firebug，响应为 409 Conflict (Expected)。但是，PUT 请求下的响应选项卡是空的。

现在，为什么响应是空的？我确实在response.printWriter 中写了错误，并刷新并关闭了它。

Answer 1

当出现错误时，我认为您不会看到任何错误。你会得到相应的错误代码。根据 HTTP 规范：这里是 link 用于 HTTP 规范。

如果创建了新资源，源服务器必须通知 用户代理通过 201 (Created) 响应。如果现有资源 被修改，200 (OK) 或 204 (No Content) 响应代码 应该发送以指示请求成功完成。如果 无法使用 Request-URI 创建或修改资源， 应该给出一个适当的错误响应，以反映 问题的性质

Answer 2

从Javadoc 到HttpServletResponse.setStatus：

容器清除缓冲区并设置 Location 标头，保留 cookie 和其他标头。

在将状态消息写入响应编写器之前尝试调用setStatus。