使用GSON库转换Java对象为JSON对象的进阶实例详解
更新时间：2016年06月22日 11:14:37 作者：李坤
这篇文章主要介绍了使用GSON库转换Java对象为JSON对象的进阶实例详解,包括注册TypeAdapter及处理Enum类型等实际运用中可能遇到的一些复杂问题,需要的朋友可以参考下
对List和map等结构的常用转换操作基本上可以满足我们处理的绝大多数需求,但有时项目中对json有特殊的格式规定.比如下面的json串解析:
[{"tableName":"students","tableData":[{"id":1,"name":"李坤","birthDay":"Jun 22, 2012 9:54:49 PM"},{"id":2,"name":"曹贵生","birthDay":"Jun 22, 2012 9:54:49 PM"},{"id":3,"name":"柳波","birthDay":"Jun 22, 2012 9:54:49 PM"}]},{"tableName":"teachers","tableData":[{"id":1,"name":"米老师","title":"教授"},{"id":2,"name":"丁老师","title":"讲师"}]}]
分析之后我们发现普通的方式都不好处理上面的json串.请看本文是如何处理的吧:
实体类:
import java.util.Date;
public class Student {
private int id;
private String name;
private Date birthDay;
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 Date getBirthDay() {
return birthDay;
}
public void setBirthDay(Date birthDay) {
this.birthDay = birthDay;
}
@Override
public String toString() {
return "Student [birthDay=" + birthDay + ", id=" + id + ", name="
+ name + "]";
}
}
public class Teacher {
private int id;
private String name;
private String title;
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 String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
@Override
public String toString() {
return "Teacher [id=" + id + ", name=" + name + ", title=" + title
+ "]";
}
}
注意这里定义了一个TableData实体类:
import java.util.List;
public class TableData {
private String tableName;
private List tableData;
public String getTableName() {
return tableName;
}
public void setTableName(String tableName) {
this.tableName = tableName;
}
public List getTableData() {
return tableData;
}
public void setTableData(List tableData) {
this.tableData = tableData;
}
}
测试类:
(仔细看将json转回为对象的实现,这里经过两次转化,第一次转回的结果是map不是我们所期望的对象,对map再次转为json后再转为对象,我引用的是Gson2.1的jar处理正常,好像使用Gson1.6的jar会报错,所以建议用最新版本)
import java.util.ArrayList;
import java.util.Date;
import java.util.List;
import com.google.gson.Gson;
import com.google.gson.reflect.TypeToken;
public class GsonTest5 {
/**
* @param args
*/
public static void main(String[] args) {
// 对象转为Json-->start
Student student1 = new Student();
student1.setId(1);
student1.setName("李坤");
student1.setBirthDay(new Date());
Student student2 = new Student();
student2.setId(2);
student2.setName("曹贵生");
student2.setBirthDay(new Date());
Student student3 = new Student();
student3.setId(3);
student3.setName("柳波");
student3.setBirthDay(new Date());
List<Student> stulist = new ArrayList<Student>();
stulist.add(student1);
stulist.add(student2);
stulist.add(student3);
Teacher teacher1 = new Teacher();
teacher1.setId(1);
teacher1.setName("米老师");
teacher1.setTitle("教授");
Teacher teacher2 = new Teacher();
teacher2.setId(2);
teacher2.setName("丁老师");
teacher2.setTitle("讲师");
List<Teacher> teacherList = new ArrayList<Teacher>();
teacherList.add(teacher1);
teacherList.add(teacher2);
TableData td1 = new TableData();
td1.setTableName("students");
td1.setTableData(stulist);
TableData td2 = new TableData();
td2.setTableName("teachers");
td2.setTableData(teacherList);
List<TableData> tdList = new ArrayList<TableData>();
tdList.add(td1);
tdList.add(td2);
Gson gson = new Gson();
String s = gson.toJson(tdList);
System.out.println(s);
// 结果:[{"tableName":"students","tableData":[{"id":1,"name":"李坤","birthDay":"Jun 22, 2012 10:44:16 AM"},{"id":2,"name":"曹贵生","birthDay":"Jun 22, 2012 10:44:16 AM"},{"id":3,"name":"柳波","birthDay":"Jun 22, 2012 10:44:16 AM"}]},{"tableName":"teachers","tableData":[{"id":1,"name":"米老师","title":"教授"},{"id":2,"name":"丁老师","title":"讲师"}]}]
// 对象转为Json-->end
// /////////////////////////////////////////////////////////////////////
// 将json转为数据-->start
List<TableData> tableDatas2 = gson.fromJson(s,
new TypeToken<List<TableData>>() {
}.getType());
for (int i = 0; i < tableDatas2.size(); i++) {
TableData entityData = tableDatas2.get(i);
String tableName = entityData.getTableName();
List tableData = entityData.getTableData();
String s2 = gson.toJson(tableData);
// System.out.println(s2);
// System.out.println(entityData.getData());
if (tableName.equals("students")) {
System.out.println("students");
List<Student> retStuList = gson.fromJson(s2,
new TypeToken<List<Student>>() {
}.getType());
for (int j = 0; j < retStuList.size(); j++) {
System.out.println(retStuList.get(j));
}
} else if (tableName.equals("teachers")) {
System.out.println("teachers");
List<Teacher> retTchrList = gson.fromJson(s2,
new TypeToken<List<Teacher>>() {
}.getType());
for (int j = 0; j < retTchrList.size(); j++) {
System.out.println(retTchrList.get(j));
}
}
}
// Json转为对象-->end
}
}
输出结果:
[{"tableName":"students","tableData":[{"id":1,"name":"李坤","birthDay":"Jun 22, 2012 10:04:12 PM"},{"id":2,"name":"曹贵生","birthDay":"Jun 22, 2012 10:04:12 PM"},{"id":3,"name":"柳波","birthDay":"Jun 22, 2012 10:04:12 PM"}]},{"tableName":"teachers","tableData":[{"id":1,"name":"米老师","title":"教授"},{"id":2,"name":"丁老师","title":"讲师"}]}]
students
Student [birthDay=Fri Jun 22 22:04:12 CST 2012, id=1, name=李坤]
Student [birthDay=Fri Jun 22 22:04:12 CST 2012, id=2, name=曹贵生]
Student [birthDay=Fri Jun 22 22:04:12 CST 2012, id=3, name=柳波]
teachers
Teacher [id=1, name=米老师, title=教授]
Teacher [id=2, name=丁老师, title=讲师]
注册TypeAdapter及处理Enum类型
枚举类型给我们的程序带来了好处,如何用Gson来实现与Json的互转呢?请看本文.
本文重点掌握如何自己写一个TypeAdapter及注册TypeAdapter和处理Enum类型.
实体类:
public enum PackageState {
PLAY, UPDATE, UPDATING, DOWNLOAD, DOWNLOADING,
}
public class PackageItem {
private String name;
private PackageState state;
private String size;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public PackageState getState() {
return state;
}
public void setState(PackageState state) {
this.state = state;
}
public String getSize() {
return size;
}
public void setSize(String size) {
this.size = size;
}
@Override
public String toString() {
return "PackageItem [name=" + name + ", size=" + size + ", state="
+ state + "]";
}
}
自己写一个转换器实现JsonSerializer<T>接口和jsonDeserializer<T>接口:
import java.lang.reflect.Type;
import com.google.gson.JsonDeserializationContext;
import com.google.gson.JsonDeserializer;
import com.google.gson.JsonElement;
import com.google.gson.JsonParseException;
import com.google.gson.JsonPrimitive;
import com.google.gson.JsonSerializationContext;
import com.google.gson.JsonSerializer;
public class EnumSerializer implements JsonSerializer<PackageState>,
JsonDeserializer<PackageState> {
// 对象转为Json时调用,实现JsonSerializer<PackageState>接口
@Override
public JsonElement serialize(PackageState state, Type arg1,
JsonSerializationContext arg2) {
return new JsonPrimitive(state.ordinal());
}
// json转为对象时调用,实现JsonDeserializer<PackageState>接口
@Override
public PackageState deserialize(JsonElement json, Type typeOfT,
JsonDeserializationContext context) throws JsonParseException {
if (json.getAsInt() < PackageState.values().length)
return PackageState.values()[json.getAsInt()];
return null;
}
}
测试类:
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
public class GsonTest6 {
public static void main(String[] args) {
GsonBuilder gsonBuilder = new GsonBuilder();
gsonBuilder.registerTypeAdapter(PackageState.class,
new EnumSerializer());
Gson gson = gsonBuilder.create();
PackageItem item = new PackageItem();
item.setName("item_name");
item.setSize("500M");
item.setState(PackageState.UPDATING);// 这个 state是枚举值
String s = gson.toJson(item);
System.out.println(s);
System.out.println("--------------------------------");
PackageItem retItem = gson.fromJson(s, PackageItem.class);
System.out.println(retItem);
}
}
输出结果(结果中已经将state的对应枚举类型转为了int类型):
{"name":"item_name","state":2,"size":"500M"}
--------------------------------
PackageItem [name=item_name, size=500M, state=UPDATING]
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