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";