JavaでJsonをリスト、マップ、エンティティに相互に変換する方法

        <dependency>
            <groupId>com.google.code.gson</groupId>
            <artifactId>gson</artifactId>
            <version>2.8.6</version>
        </dependency>

public class Person
{
    private String name;
    private int age;
    private boolean isMale;
    private List<String> hobbies;

    // 省略构造器和getter/setter方法，注意重写toString方法，便于查看控制台输出。

    @Override
    public String toString()
    {
        final StringBuilder sb = new StringBuilder("Person{");
        sb.append("name=&#39;").append(name).append(&#39;\&#39;&#39;);
        sb.append(", age=").append(age);
        sb.append(", isMale=").append(isMale);
        sb.append(", hobbies=").append(hobbies);
        sb.append(&#39;}&#39;);
        return sb.toString();
    }
}

@Test
public void testBeanToJson()
{
    // 创建Bean
    Person p = new Person("艾伦·耶格尔", 16, true, Arrays.asList("自由", "迫害莱纳"));
    // 创建Gson对象
    Gson gson = new Gson();
    // 调用Gson的String toJson(Object)方法将Bean转换为json字符串
    String pJson = gson.toJson(p);

    System.out.println(pJson);
    // {"name":"艾伦·耶格尔","age":16,"isMale":true,"hobbies":["自由","迫害莱纳"]}
}

// 调用Gson的 <T> t fromJson(String, Class)方法，将Json串转换为对象
Person person = gson.fromJson(pJson, Person.class);
System.out.println(person);
// Person{name=&#39;艾伦·耶格尔&#39;, age=16, isMale=true, hobbies=[自由, 迫害莱纳]}

@Test
public void testListToJson()
{
    // 先准备一个List集合
    List<Person> list = new ArrayList<Person>();
    list.add(new Person("三笠·阿克曼", 16, false, Arrays.asList("砍巨人", "保护艾伦")));
    list.add(new Person("阿明·阿诺德", 16, true, Arrays.asList("看书", "玩海螺")));
    System.out.println(list);
    // 创建Gson实例
    Gson gson = new Gson();
    // 调用Gson的toJson方法
    String listJson = gson.toJson(list);
    System.out.println(listJson);
    // [{"name":"三笠·阿克曼","age":16,"isMale":false,"hobbies":["砍巨人","保护艾伦"]},{"name":"阿明·阿诺德","age":16,"isMale":true,"hobbies":["看书","玩海螺"]}]
}

......// 此处延续以上代码
List fromJson = gson.fromJson(listJson, List.class);
System.out.println(fromJson.get(0).getClass());
// class com.google.gson.internal.LinkedTreeMap

......// 此处延续以上代码
// 调用Gson的 T fromJson(String, Type)将List集合的json串反序列化为List对象
List<Person> plist = gson.fromJson(listJson, new TypeToken<List<Person>>(){}.getType());
System.out.println(plist);
// [Person{name=&#39;三笠·阿克曼&#39;, age=16, isMale=false, hobbies=[砍巨人, 保护艾伦]}, Person{name=&#39;阿明·阿诺德&#39;, age=16, isMale=true, hobbies=[看书, 玩海螺]}]

@Test
public void testMapToJson()
{
    Map<String, Person> map = new HashMap<>();
    map.put("p1", new Person("利威尔·阿克曼", 35, true, Arrays.asList("砍猴儿", "打扫卫生")));
    map.put("p2", new Person("韩吉·佐耶", 33, false, Arrays.asList("研究巨人", "讲故事")));

    Gson gson = new Gson();
    String mapJson = gson.toJson(map);

    System.out.println(mapJson);
    // {"p1":{"name":"利威尔·阿克曼","age":35,"isMale":true,"hobbies":["砍猴儿","打扫卫生"]},"p2":{"name":"韩吉·佐耶","age":33,"isMale":false,"hobbies":["研究巨人","讲故事"]}}
    Map<String, Person> jsonMap = gson.fromJson(mapJson, new TypeToken<Map<String, Person>>() { }.getType());
    System.out.println(jsonMap);
}