jackson简单使用,对象转json,json转对象,json转list
http://www.flypeng.com win10系统 发布时间:2017-07-28 11:24 来源:未知 浏览:加载中

添加jackson依赖:

// https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-core
compile group: 'com.fasterxml.jackson.core', name: 'jackson-core', version: '2.8.2'
// https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-databind
compile group: 'com.fasterxml.jackson.core', name: 'jackson-databind', version: '2.8.2'
// https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-annotations
compile group: 'com.fasterxml.jackson.core', name: 'jackson-annotations', version: '2.8.2'

看到fasterxml还以为找错依赖,还以为和com.alibaba:fastjson这个有啥联系,还以为是一个叫做jack的人写的。为啥有三个依赖,当发现大多数的框架都依赖于jackson来处理json转换的时候就自然而然的当做理所当然了。

 

 

POJO序列化为json字符串:

准备一个POJO:

@JsonIgnoreProperties(ignoreUnknown = true)
class User implements Serializable {
    private static final long serialVersionUID = -5952920972581467417L;
    private String name;

    public User() {
    }

    public User(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }

    @Override
    public String toString() {
        return "User{" +
                "name=" + name +
                '}';
    }
}
  • @JsonIgnoreProperties(ignoreUnknown = true) 是为了反序列化的时候,如果遇到不认识的filed,忽略之
  • 无参构造函数是为了在反序列化的时候,jackson可以创建POJO实例
  • getter方法是为了序列化的时候,jackson可以获取filed值
  • toString是方便我自己debug看显示
  • 至于Serializable,习惯的给实体增加一个持久化的能力。

 

通过write来转化成jason字符串:

String expected = "{\"name\":\"Test\"}";
String test = mapper.writeValueAsString(new User("Test"));
Assert.assertEquals(expected, test);

通过read来parse json字符串为POJO对象:

User user = mapper.readValue(expected, User.class);
Assert.assertEquals("Test", user.getName());

 

 

jsonArray转换成Array数组:

String expected = "[{\"name\":\"Ryan\"},{\"name\":\"Test\"},{\"name\":\"Leslie\"}]";
ArrayType arrayType = mapper.getTypeFactory().constructArrayType(User.class);
User[] users = mapper.readValue(expected, arrayType);
Assert.assertEquals("Ryan", users[0].getName());

 

jsonArray转换成List<>泛型:

expected="[{\"a\":12},{\"b\":23},{\"name\":\"Ryan\"}]";
CollectionType listType = mapper.getTypeFactory().constructCollectionType(ArrayList.class, User.class);
//the sieze of the list is dependon the str json length although the json content is not the POJO type maybe
List<User> userList = mapper.readValue(expected, listType);
Assert.assertEquals(3, userList.size());
Assert.assertNull(userList.get(0).getName());
Assert.assertEquals("Ryan",userList.get(2).getName());

 

jackson默认将对象转换为LinkedHashMap:

String expected = "[{\"name\":\"Ryan\"},{\"name\":\"Test\"},{\"name\":\"Leslie\"}]";
ArrayList arrayList = mapper.readValue(expected, ArrayList.class);
Object o = arrayList.get(0);
Assert.assertTrue(o instanceof LinkedHashMap);

 

So do it,and change it,no regret!
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