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!'}");
    }
}

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