json学习六——>Java 读写json格式的文件方法详解

一、要解决这个问题首先要知道json格式是什么？ 

JSON格式： 
比如学生有学号，姓名，性别等。 
用json表示则为： 
{"studno":"11111","studname":"wwww","studsex":"男"}(各个字段都是字符型） 

这代表一个学生的信息。 

如果多个呢？ 

[{"studno":"122222","studname":"wwww","studsex":"男"}, 
{"studno":"11111","studname":"xxxx","studsex":"男"}, 
{"studno":"33333","studname":"ssss","studsex":"男"}] 

这就是json格式。 

二、那如何操作json格式的文件呢？ 

这个更简单了，说白了就是直接读写文件，再把读出来的文件内容格式化成json就可以了。 

三、具体操作。 

1.我有一个实体类，如下： 

public class ElectSet { 
public String xueqi; 
public String xuenian; 
public String startTime; 
public String endTime; 
public int menshu; 
public String isReadDB; 
//{"xueqi":,"xuenian":,"startTime":,"endTime":,"renshu":,"isReadDB":} 
public String getXueqi() { 
    return xueqi; 
} 
public void setXueqi(String xueqi) { 
    this.xueqi = xueqi; 
} 
public String getXuenian() { 
    return xuenian; 
} 
public void setXuenian(String xuenian) { 
    this.xuenian = xuenian; 
} 
public String getStartTime() { 
    return startTime; 
} 
public void setStartTime(String startTime) { 
    this.startTime = startTime; 
} 
public String getEndTime() { 
    return endTime; 
} 
public void setEndTime(String endTime) { 
    this.endTime = endTime; 
} 
public int getMenshu() { 
    return menshu; 
} 
public void setMenshu(int menshu) { 
    this.menshu = menshu; 
} 
public String getIsReadDB() { 
    return isReadDB; 
} 
public void setIsReadDB(String isReadDB) { 
    this.isReadDB = isReadDB; 
} 

} 

2.有一个json格式的文件，存的就是他的信息，如下 

Sets.json: 
{"xuenian":"2007-2008","xueqi":"1","startTime":"2009-07-19 08:30","endTime":"2009-07-22 18:00","menshu":"10","isReadDB":"Y"} 

3.具体操作. 
/* 
* 取出文件内容，填充对象 
*/ 
public ElectSet findElectSet(String path){ 
    ElectSet electset=new ElectSet(); 
    String sets=ReadFile(path);//获得json文件的内容 
    JSONObject jo=JSONObject.fromObject(sets);//格式化成json对象 
    //System.out.println("------------" jo); 
    //String name = jo.getString("xuenian"); 
    //System.out.println(name); 
    electset.setXueqi(jo.getString("xueqi")); 
    electset.setXuenian(jo.getString("xuenian")); 
    electset.setStartTime(jo.getString("startTime")); 
    electset.setEndTime(jo.getString("endTime")); 
    electset.setMenshu(jo.getInt("menshu")); 
    electset.setIsReadDB(jo.getString("isReadDB")); 
    return electset; 
} 
//设置属性，并保存 
public boolean setElect(String path,String sets){ 
    try { 
     writeFile(path,sets); 
     return true; 
    } catch (IOException e) { 
     // TODO Auto-generated catch block 
     e.printStackTrace(); 
     return false; 
    } 
} 
//读文件，返回字符串 
public String ReadFile(String path){ 
     File file = new File(path); 
     BufferedReader reader = null; 
     String laststr = ""; 
     try { 
      //System.out.println("以行为单位读取文件内容，一次读一整行："); 
      reader = new BufferedReader(new FileReader(file)); 
      String tempString = null; 
      int line = 1; 
      //一次读入一行，直到读入null为文件结束 
      while ((tempString = reader.readLine()) != null) { 
       //显示行号 
       System.out.println("line " line ": " tempString); 
       laststr = laststr tempString; 
       line ; 
      } 
      reader.close(); 
     } catch (IOException e) { 
      e.printStackTrace(); 
     } finally { 
      if (reader != null) { 
       try { 
        reader.close(); 
       } catch (IOException e1) { 
       } 
      } 
     } 
     return laststr; 
} 
          //把json格式的字符串写到文件 
public void writeFile(String filePath, String sets) throws IOException { 
     FileWriter fw = new FileWriter(filePath); 
     PrintWriter out = new PrintWriter(fw); 
     out.write(sets); 
     out.println(); 
     fw.close(); 
     out.close(); 
    } 

4.调用，使用（在网站的controller里调用的） 

//取出json对象 
public void GetElectSettings(HttpServletRequest request, 
     HttpServletResponse response) throws Exception { 
    ElectSet electset=new ElectSet(); 
    String absPath = request.getRealPath("\\"); 
    String filePath = absPath "public\\sets\\electSets.json"; 
    electset=businessService.findElectSets(filePath);//这里是调用，大家自己改改，我调用的业务层 的。 
    JSONArray jsonItems = new JSONArray(); 
    jsonItems.add(electset); 
    JSONObject jo=new JSONObject(); 
    jo.put("data", jsonItems); 
    System.out.println(jo); 
    request.setCharacterEncoding("utf-8"); 
    response.setContentType("application/json;charset=utf-8"); 
    PrintWriter out = response.getWriter(); 
    out.print(jo); 
} 

//修改json文件 
public void ChangeElectSet(HttpServletRequest request, 
     HttpServletResponse response) throws Exception { 
    request.setCharacterEncoding("UTF-8"); 
    response.setContentType("text/json;charset=utf-8"); 
    log.info("reach ChangeElectSet"); 
    String json = (String) request.getParameter("json").trim(); 
    log.info("Change ElectSet"); 
    log.info(json); 
    ElectSet sets = new ElectSet(); 
    JSONObject jsonObject = JSONObject.fromObject(json); 
    sets = (ElectSet) JSONObject.toBean(jsonObject, ElectSet.class); 
    if(sets.getIsReadDB()=="false"){ 
     sets.setIsReadDB("否"); 
    } 
    else{ 
     sets.setIsReadDB("是"); 
    } 
    String changes="{\"xuenian\":\"";//因为json的属性要用引号，所以要用\"转义一下 
    changes =sets.getXuenian() "\",\"xueqi\":\"" sets.getXueqi() "\",\"startTime\":\"" sets.getStartTime() "\",\"endTime\":\"" sets.getEndTime() "\",\"menshu\":\"" sets.getMenshu() "\",\"isReadDB\":\"" sets.getIsReadDB() "\"}"; 
    System.out.println(changes); 
    String absPath = request.getRealPath("\\"); 
    String filePath = absPath "public\\sets\\electSets.json"; 
    if(businessService.ChangeElectSets(filePath, changes)){ 
     log.info("选课设置修改成功"); 
     request.setCharacterEncoding("UTF-8"); 
     response.setContentType("text/json;charset=utf-8"); 
     response.getWriter().write("{success: true}"); 
    } else { 
     response.getWriter().write("{errors:'选课设置修改失败，请重新尝试!'}"); 
    } 
} 

摘自红色黑客联盟(www.7747.net) 原文：http://www.7747.net/kf/201009/74381.html