類：AjaxExchange
作用：將後臺取到的資料以JSON或HTML的形式返回

package org.sun.com;

import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import javax.servlet.http.HttpServletResponse;

import net.sf.json.JSONArray;
import net.sf.json.JsonConfig;

public class AjaxExchange {
    
    // 轉換成HTML形式返回，引數為String型別
    public static void printData(HttpServletResponse response, String msg) {  
        try {  
        	// 跨域配置
            response.setHeader("Access-Control-Allow-Origin","*");
            response.setHeader("Access-Control-Allow-Methods", "POST, PUT, GET, OPTIONS, DELETE");
            response.setHeader("Access-Control-Allow-Credentials", "true");
            response.setHeader("Access-Control-Max-Age", "3600");	// 保持跨域Ajax時的Cookie
            response.setHeader("Access-Control-Allow-Headers", "x-auth-token, x-requested-with,Authorization,Origin, Accept, Content-Type,x-xsrf-token");

            response.setContentType("text/html;charset=utf-8");  
            response.setCharacterEncoding("UTF-8");  
            PrintWriter out = new PrintWriter(new OutputStreamWriter(response.getOutputStream(), "UTF-8"));  
            out.println(msg);  
            out.close();  
        } catch (Exception e) {    
            e.printStackTrace();  
        }  
   }  

    // 將任意型別的item轉換成JSON並返回  
    public static void printDataJason(HttpServletResponse response, Object item) {  
        try {  
        	// 跨域配置
            response.setHeader("Access-Control-Allow-Origin","*");
            response.setHeader("Access-Control-Allow-Methods", "POST, PUT, GET, OPTIONS, DELETE");
            response.setHeader("Access-Control-Allow-Credentials", "true");
            response.setHeader("Access-Control-Max-Age", "3600");	// 保持跨域Ajax時的Cookie
            response.setHeader("Access-Control-Allow-Headers", "x-auth-token, x-requested-with,Authorization,Origin, Accept, Content-Type,x-xsrf-token");

        	response.setContentType("text/json;charset=utf-8");  
        	response.setCharacterEncoding("UTF-8");  
        	PrintWriter out = new PrintWriter(new OutputStreamWriter(response.getOutputStream(), "UTF-8"));  
    		
        	// currentUser裡面有迴圈導致json處理不了
    		JsonConfig jsonConfig = new JsonConfig();  //建立配置檔案
    		jsonConfig.setIgnoreDefaultExcludes(false);  //設定預設忽略
    		jsonConfig.setExcludes(new String[]{"currentUser"});
    		
        	JSONArray jsonArr = JSONArray.fromObject(item, jsonConfig);
            out.println(jsonArr); 
  
            out.close();  
        } catch (Exception e) {    
        	e.printStackTrace();    
        }  
	}  

    // 帶JsonConfig的JSON轉換
    public static void printDataJason(HttpServletResponse response, Object item, JsonConfig jsonConfig) {  
        try {  
        	// 跨域配置
            response.setHeader("Access-Control-Allow-Origin","*");
            response.setHeader("Access-Control-Allow-Methods", "POST, PUT, GET, OPTIONS, DELETE");
            response.setHeader("Access-Control-Allow-Credentials", "true");
            response.setHeader("Access-Control-Max-Age", "3600");	// 保持跨域Ajax時的Cookie
            response.setHeader("Access-Control-Allow-Headers", "x-auth-token, x-requested-with,Authorization,Origin, Accept, Content-Type,x-xsrf-token");

        	response.setContentType("text/json;charset=utf-8");  
        	response.setCharacterEncoding("UTF-8");  
        	PrintWriter out = new PrintWriter(new OutputStreamWriter(response.getOutputStream(), "UTF-8"));  
           
        	JSONArray jsonArr = JSONArray.fromObject(item, jsonConfig);
            out.println(jsonArr); 
  
            out.close();  
        } catch (Exception e) {    
        	e.printStackTrace();    
        }  
	}
}
 

這裡第二個方法和第三個方法很像，區別在於第三個方法多了個JsonConfig的引數，這是用來設定Json轉換時的一些引數的。

我在返回資料轉Json的時候到這樣的問題：
我想返回的引數是型別A，但是型別A繼承了型別B，型別B裡面有些資料是型別C，型別C裡面有些型別是型別D
結果變成了這樣A→B→C→D→...
JSONArray轉換的時候，會根據這個順序迴圈，把型別ABCD...裡面的資料都JSON化。
如果A→B→C→D→C時，C和D產生迴圈的話，JSON就無法轉換了。

        	// currentUser裡面有迴圈導致json處理不了
    		JsonConfig jsonConfig = new JsonConfig();  //建立配置檔案
    		jsonConfig.setIgnoreDefaultExcludes(false);  //設定預設忽略
    		jsonConfig.setExcludes(new String[]{"currentUser"});
 

我找到了發生型別迴圈出錯的引數並在方法2中寫死了。也可以在外面設定出錯的引數並傳到方法3中。 呼叫方法如下：

    @RequestMapping(value = "/restful/getQuestion")
    public void getQuestion(HttpServletRequest request, HttpServletResponse response) {

    	RestfulResult restfulResult = new RestfulResult();
    	
    	try{
                // 將資料取出放入restfulResult
	        ...
                restfulResult.setData(...);
    	}
	catch(Exception ex)
	{
	  	restfulResult.setResult("Error");
	    	restfulResult.setMessage(ex.getMessage());
	}

    	AjaxExchange.printDataJason(response, restfulResult);
    } 
 

追加：

也可以在Entity定義的時候，加上@jsonignore

json會在轉換的時候自動忽略此欄位