通透Gson@Expose注解、@SerializedName、解析json数据
在讲如何解析数据之前，先描述一下gson中的两个注解@Expose和@SerializedName。
@Expose注解的作用：区分实体中不想被序列化的属性，其自身包含两个属性deserialize(反序列化)和serialize（序列化），默认都为true。
使用 new GsonBuilder().excludeFieldsWithoutExposeAnnotation().create();创建Gson对象，没有@Expose注释的属性将不会被序列化.。
private class User{
private int id;
@Expose
private String name;
.......
}@SerializedName注解的作用：定义属性序列化后的名称
public class User{
private int id;
@Expose
@SerializedName("username")
private String name;
.......
}另外想要不序列化某个属性，也可以使用transient。
private class User{
private int id;
private transient String name;
.......
}下面列举一下gson如何解析json数据的
//转换器
GsonBuilder builder = new GsonBuilder();
// 不转换没有 @Expose 注解的字段
builder.excludeFieldsWithoutExposeAnnotation();
Gson gson = builder.create();
//1、对象转string
Student stu = new Student();
stu.setStudentId(333);
stu.setStudentName("qqq");
String stuStr = gson.toJson(stu);
System.out.println(stuStr); //{"studentName":"qqq","studentId":333}
//2、string转对象
Student user2 = gson.fromJson(stuStr, Student.class);
System.out.println(user2);
String stuTemp = "{\"studentName\":\"qqq2\",\"studentId\":3335}";
Student user4 = gson.fromJson(stuTemp, Student.class);
System.out.println(user4);
//3、对象List转string
List testBeanList = new ArrayList();
Student testBean = new Student();
testBean.setStudentId(555);
testBean.setStudentName("552");
testBeanList.add(testBean);
//Gson gsonList = new Gson();
Type type = new TypeToken>(){}.getType(); //指定集合对象属性
String beanListToJson = gson.toJson(testBeanList, type);
System.out.println(beanListToJson); //[{"studentName":"552","studentId":555}]
//集合string转对象list
List testBeanListFromJson = gson.fromJson(beanListToJson, type);
System.out.println(testBeanListFromJson); //[555:552]
//4、集合如果不指定类型 默认为String
List testList = new ArrayList();
testList.add("first");
testList.add("second");
String listToJson = gson.toJson(testList);
System.out.println(listToJson); //["first","second"]
//5、集合字符串转回来需要指定类型
List testList2 = (List) gson.fromJson(listToJson,new TypeToken>() {}.getType());
System.out.println(testList2);
//6、 将HashMap字符串转换为 JSON
Map testMap = new HashMap();
testMap.put("id", "id.first");
testMap.put("name", "name.second");
String mapToJson = gson.toJson(testMap);
System.out.println(mapToJson); //{"id":"id.first","name":"name.second"}
//7、stringMap转对象
Map userMap2 = (Map) gson.fromJson(mapToJson,new TypeToken>() {}.getType());
System.out.println(userMap2); //{id=id.first, name=name.second}
//8、对象含有普通对象、集合、map情况
Student user1 = new Student();
user1.setStudentId(1001);
user1.setStudentName("张三");
Student user3 = new Student();
user3.setStudentId(1002);
user3.setStudentName("李四");
Map userMap = new HashMap();
userMap.put("user1", user1);
userMap.put("user3", user3);
List userList = new ArrayList();
userList.add(user1);
userList.add(user3);
Teacher groupBean = new Teacher();
groupBean.setStudent(user1);
groupBean.setStus(userList);
groupBean.setMap((HashMap)userMap);
//groupBean.setUserList(userList);
Gson gsonGroup = new Gson();
String sGroupBean = gsonGroup.toJson(groupBean, new TypeToken() {}.getType());
System.out.println(sGroupBean);
/*{"stus":[{"studentName":"张三","studentId":1001},{"studentName":"李四","studentId":1002}],"student":{"studentName":"张三","studentId":1001},"map":{"user3":{"studentName":"李四","studentId":1002},"user1":{"studentName":"张三","studentId":1001}},"id":0,"age":0}*/
//9、复杂对象string转对象
Teacher groupBean2 = (Teacher) gson.fromJson(sGroupBean,new TypeToken() {}.getType());
System.out.println(groupBean2);
package com.andtools;
import com.google.gson.annotations.Expose;
public class Student {
@Expose
private String studentName;
@Expose
private int studentId;
public Student(){}
public Student(int studentId,String studentName){
this.setStudentId(studentId);
this.setStudentName(studentName);
}
public String toString(){
return this.getStudentId() + ":" + this.getStudentName();
}
public String getStudentName() {
return studentName;
}
public void setStudentName(String studentName) {
this.studentName = studentName;
}
public int getStudentId() {
return studentId;
}
public void setStudentId(int studentId) {
this.studentId = studentId;
}
}
package com.andtools;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import com.google.gson.annotations.Expose;
public class Teacher {
@Expose
private int id;
@Expose
private String name;
@Expose
private int age;
@Expose
private Student student;
@Expose
private List stus;
@Expose
private HashMap map;
public String toString(){
return this.getId()+":"+this.getName()+":"+this.getAge() +":"+ this.getStudent().toString() + ":" + this.getStus() + ":" + this.getMap();
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public Student getStudent() {
return student;
}
public void setStudent(Student student) {
this.student = student;
}
public List getStus() {
return stus;
}
public void setStus(List stus) {
this.stus = stus;
}
public HashMap getMap() {
return map;
}
public void setMap(HashMap map) {
this.map = map;
}
}