Ajax PUT请求收到空响应

Question

我写了一个HttpCRUDServlet，它将执行以下任务（到目前为止）。

• 响应OPTIONS方法与适当的CORS标头（service()），
• 解析，并插入在所述数据库（doPut()）PUT请求中传递的数据。

所有的功能似乎工作正常，除了客户端收到空响应。

这里的源：

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); 
    } 
} 

} 

这里的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"); 
     } 
    }); 

我使用Firebug上iceweasel 3.5.16，响应409冲突（预期）。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？我确信在response.printWriter中写入了错误，并将其刷新并关闭。

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：这里是用于HTTP Spec的link。

如果创建新的资源，源服务器必须通过201（创建）响应通知 用户代理。如果修改现有资源 ，则应发送200（OK）或204（无内容）响应代码 以指示请求的成功完成。如果 资源无法创建或请求URI， 相应的错误反应，应给予反映 性质的问题

Answer 2

从Javadoc为HttpServletResponse.setStatus修改：

容器清除缓冲区并设置位置标题，保留Cookie和其他标题。

在将状态消息写入响应写入器之前，请尝试调用setStatus。