007_支持序列化空值

1. 默认情况下, Gson生成优化的Json内容, 忽略NULL值。但是GsonBuilder使用GsonBuilder.serializeNulls()方法提供了在Json输出中显示NULL值的标志。

GsonBuilder builder = new GsonBuilder();
builder.serializeNulls();
Gson gson = builder.create();

2. 例子

2.1. 新建一个名为GsonSerializeNulls的Java项目, 同时添加相关jar包。

2.2. 新建Student.java

package com.fj.sn;

public class Student {
	private String name;
	private int age;

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

	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 String toString() {
		return "Student [name: " + name + ", age: " + age + "]";
	}
}

2.3. 新建App.java

package com.fj.sn;

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;

public class App {
	public static void main(String[] args) {
		// 创建一个学生对象
		Student student = new Student(null, 21);
		
		Gson gson = new Gson(); 
		String jsonString = gson.toJson(student);
	    System.out.println(jsonString); 
	      
		// 1. Gson构造器
		GsonBuilder builder = new GsonBuilder();
		// 2. 支持序列化空值
		builder.serializeNulls();
		// 3. 格式良好的输出
		builder.setPrettyPrinting();
		// 4. 创建Gson对象
		gson = builder.create();
		// 5. JavaBean转化为JSON字符串
		jsonString = gson.toJson(student);
		System.out.println(jsonString);
	}
}

2.4. 运行项目