Json解析详解

一，介绍

Json(JavaScript Object Notation)一种轻量级的数据交换格式。

二,Json数据的格式结构:对象和数组

1.Json对象：“Key/value"（”键/值“）对的无序集合格式

单个键值

{
"name":"xiaoming"
}

多个键值对，中间用"，"隔开(可读性好，可以看到各个值之间的联系,最后一个键值对不能加括号)

{
  "name":"xiaoming",
  "age":20
}

2，Json数组：值的有序列表

单个键值

{
  "person":[
  {"name":"xiaoming","age":10},
  {"name":"xiaoming","age":10},
  {"name":"xiaoming","age":10}
  ]
}

多个键值对

{
  "programmers":[
  {"name":"xiaoming","age":10},
  {"name":"xiaoming","age":10},
  {"name":"xiaoming","age":10}
  ]
  "student":[
  {"name":"xiaoming","age":10},
  {"name":"xiaoming","age":10},
  {"name":"xiaoming","age":10}
  ]
  "authors":[
  {"name":"xiaoming","age":10},
  {"name":"xiaoming","age":10},
  {"name":"xiaoming","age":10}
  ]
}

3.嵌套数据

{
  "name":"xiaoming",
  "age":20,
  "student":{
    "name":"xiaohong",
    "age":10
  }
}

三，解析Json数据

1.利用Android API中的JsonReader解析Json数据

Android develop 中的Example

解析嵌套数据

 [
   {
     "id": 912345678901,
     "text": "How do I read JSON on Android?",
     "geo": null,
     "user": {
       "name": "android_newb",
       "followers_count": 41
      
   },
   {
     "id": 912345678902,
     "text": "@android_newb just use android.util.JsonReader!",
     "geo": [50.454722, -104.606667],
     "user": {
       "name": "jesse",
       "followers_count": 2
     }
   }
 ]

This code implements the parser for the above structure:
 
public List readJsonStream(InputStream in) throws IOException {
     //Creates a new instance that reads a JSON-encoded stream from in.
     JsonReader reader = new JsonReader(new InputStreamReader(in, "UTF-8"));
     try {
       return readMessagesArray(reader);
       finally {
       reader.close();
     }
   }
   public List readMessagesArray(JsonReader reader) throws IOException {
     List messages = new ArrayList();
     reader.beginArray();//开始解析数组
     while (reader.hasNext()) {//// 判断是否有下一个对象
       messages.add(readMessage(reader));
     }
     reader.endArray();
     return messages;
   }
   public Message readMessage(JsonReader reader) throws IOException {
     long id = -1;
     String text = null;
     User user = null;
     List geo = null;
     reader.beginObject();
     while (reader.hasNext()) {
       String name = reader.nextName(); //获取属性名
       if (name.equals("id")) {
         id = reader.nextLong();//获取属性值，long类型，String会转化，不能转化则出粗
       } else if (name.equals("text")) {
         text = reader.nextString(); //获取属性值，String类型
       } else if (name.equals("geo") && reader.peek() != JsonToken.NULL) {
         //Returns the type of the next token without consuming it.
         geo = readDoublesArray(reader);
       } else if (name.equals("user")) {
         user = readUser(reader);
       } else {
         reader.skipValue();
       }
     }
     reader.endObject();
     return new Message(id, text, user, geo);
   }
   public List readDoublesArray(JsonReader reader) throws IOException {
     List doubles = new ArrayList();
     reader.beginArray();
     while (reader.hasNext()) {
       doubles.add(reader.nextDouble());
     }
     reader.endArray();
     return doubles;
   }
   public User readUser(JsonReader reader) throws IOException {
     String username = null;
     int followersCount = -1;
     reader.beginObject(); //开始解析
     while (reader.hasNext()) {
       String name = reader.nextName();
       if (name.equals("name")) {
         username = reader.nextString();
       } else if (name.equals("followers_count")) {
         followersCount = reader.nextInt();
       } else {
         reader.skipValue();
       }
     }
     reader.endObject(); //结束解析
     return new User(username, followersCount);
   }}

解析单个键/值对

private void jsonReaderTest() {
// 这里的Json放到string中，所以加上了转译
String jsonString = "{\"name\":\"xiaoming\",\"age\":20}";
 
JsonReader reader = new JsonReader(new StringReader(jsonString));
try {
reader.beginObject();
while (reader.nextName()) { 
String tagName = reader.nextName(); 
if (tagName.equals("name")) {
System.out.println(reader.nextString());
} else if (tagName.equals("age")) {
System.out.println(reader.nextString());
}
}
reader.endObject(); // 结束对象的解析
} catch (IOException e) {
// TODO 自动生成的 catch 块
e.printStackTrace();
}
}

解析多个键/值对

private void jsonReaderTest() {
        // 这里的Json放到string中，所以加上了转译
        String jsonString = "[{\"name\":\"xiaoming\",\"age\":20},{\"name\":\"xiaohong\",\"age\":10}]";
 
        JsonReader reader = new JsonReader(new StringReader(jsonString));
        try {
            reader.beginArray(); 
            while (reader.hasNext()) { 
                reader.beginObject();
                while (reader.hasNext()) {
                    String tagName = reader.nextName(); 
                    if (tagName.equals("name")) {
                        System.out.println(reader.nextString());
                    } else if (tagName.equals("age")) {
                        System.out.println(reader.nextString());
                    }
                }
                reader.endObject(); // 结束对象的解析
            }
            reader.endArray(); // 结束解析当前数组
        } catch (IOException e) {
            // TODO 自动生成的 catch 块
            e.printStackTrace();
        }
    }

2,通过Gson解析Json

1.解析单个键/值对

{
  "name":"xiaoming",
  "age":20
}

根据数据的格式定义一个类

(类里面的成员变量必须和Json字段里面的name,age一样，会自动对应)

 
public class Student {
public Student(String name,int age){
this.name = name;
this.age = age;
}
public String name;
public int age;
}

解析

String jsonData = "{\"name\":\"xiaoming\",\"age\":10}";
Student student = gson.fromJson(jsonData, Student.class);
if (student.name.equals("xiaoming")) {
   System.out.println(student.age);
}
System.out.println(student.age+student.name);

2,解析多个键/值对

//解析数组
String jsonDatas = "[{\"name\":\"xiaoming\",\"age\":10},{\"name\":\"xiaohong\",\"age\":15}]";
Student[] students = gson.fromJson(jsonDatas, Student[].class);
for (int i = 0; i < students.length; i++) {
System.out.println(students[i].age);
System.out.println(students[i].name);
}
 
//解析列表
ArrayList<Student> list = gson.fromJson(jsonDatas,new TypeToken<ArrayList<Student>>(){}.getType());
for (int i = 0; i < list.size(); i++) {
System.out.println(list.get(i).name);
System.out.println(list.get(i).age);
}

3,解析嵌套数据

String jsonData2 = "{\"name\":\"xiaoming\",\"age\":10,\"middle\":{\"name\":\"lili\",\"age\":20}}";
StudentMiddle studentMiddle = gson.fromJson(jsonData2, StudentMiddle.class);
System.out.println(studentMiddle.middle.name);

public class StudentMiddle {
public String name;
public int age;
public Middle middle;
public class Middle{
public String name;
public int age;
}
}