在json的解析等处理方面,我更喜欢用阿里巴巴的Fastjson。Jackson也有许多实用的功能。今天整理几个比较常用的jackson实用功能:
示例代码
@RequestMapping("getuser")
@ResponseBody
public User getUser() {
User user = new User();
user.setUserName("mrbird");
user.setBirthday(new Date());
return user;
}
public class User implements Serializable {
private static final long serialVersionUID = 6222176558369919436L;
private String userName;
private int age;
private String password;
private Date birthday;
...
}
# 项目中统一返回时间格式化
访问getuser页面输出:
{"userName":"mrbird","age":0,"password":null,"birthday":1522634892365}
可看到时间默认以时间戳的形式输出,如果想要改变这个默认行为,我们可以自定义一个ObjectMapper来替代:
import java.text.SimpleDateFormat;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import com.fasterxml.jackson.databind.ObjectMapper;
@Configuration
public class JacksonConfig {
@Bean
public ObjectMapper getObjectMapper(){
ObjectMapper mapper = new ObjectMapper();
mapper.setDateFormat(new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"));
return mapper;
}
}
上面配置获取了ObjectMapper对象,并且设置了时间格式。再次访问getuser,页面输出:
{"userName":"mrbird","age":0,"password":null,"birthday":"2018-04-02 10:14:24"}
# Jackson注解
- @JsonProperty
作用在属性上,用来为JSON Key指定一个别名。
@JsonProperty("bth")
private Date birthday;
再次访问getuser页面输出:
{"userName":"mrbird","age":0,"password":null,"bth":"2018-04-02 10:38:37"}
- @Jsonlgnore
作用在属性上,用来忽略此属性。
@JsonIgnore
private String password;
再次访问getuser页面输出:
{"userName":"mrbird","age":0,"bth":"2018-04-02 10:40:45"}
password属性已被忽略。
- @JsonIgnoreProperties
忽略一组属性,作用于类上,比如JsonIgnoreProperties({ “password”, “age” })。
@JsonIgnoreProperties({ "password", "age" })
public class User implements Serializable {
...
}
再次访问getuser页面输出:
{"userName":"mrbird","bth":"2018-04-02 10:45:34"}
- @JsonFormat
用于日期格式化
@JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss")
private Date birthday;
- @JsonNaming
用于指定一个命名策略,作用于类或者属性上。Jackson自带了多种命名策略,你可以实现自己的命名策略,比如输出的key 由Java命名方式转为下面线命名方法 —— userName转化为user-name。
@JsonNaming(PropertyNamingStrategy.LowerCaseWithUnderscoresStrategy.class)
public class User implements Serializable {
...
}
再次访问getuser页面输出:
{"user_name":"mrbird","bth":"2018-04-02 10:52:12"}
- @JsonSerialize
指定一个实现类来自定义序列化。类必须实现JsonSerializer接口,代码如下:
import java.io.IOException;
import com.example.pojo.User;
import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.JsonSerializer;
import com.fasterxml.jackson.databind.SerializerProvider;
public class UserSerializer extends JsonSerializer<User> {
@Override
public void serialize(User user, JsonGenerator generator, SerializerProvider provider)
throws IOException, JsonProcessingException {
generator.writeStartObject();
generator.writeStringField("user-name", user.getUserName());
generator.writeEndObject();
}
}
上面的代码中我们仅仅序列化userName属性,且输出的key是user-name。 使用注解@JsonSerialize来指定User对象的序列化方式:
@JsonSerialize(using = UserSerializer.class)
public class User implements Serializable {
...
}
再次访问getuser页面输出:
{"user-name":"mrbird"}
- @JsonDeserialize
import java.io.IOException;
import com.example.pojo.User;
import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.JsonDeserializer;
import com.fasterxml.jackson.databind.JsonNode;
public class UserDeserializer extends JsonDeserializer<User> {
@Override
public User deserialize(JsonParser parser, DeserializationContext context)
throws IOException, JsonProcessingException {
JsonNode node = parser.getCodec().readTree(parser);
String userName = node.get("user-name").asText();
User user = new User();
user.setUserName(userName);
return user;
}
}
使用注解@JsonDeserialize来指定User对象的序列化方式:
@JsonDeserialize (using = UserDeserializer.class)
public class User implements Serializable {
...
}
测试:
@Autowired
ObjectMapper mapper;
@RequestMapping("readjsonasobject")
@ResponseBody
public String readJsonAsObject() {
try {
String json = "{\"user-name\":\"mrbird\"}";
User user = mapper.readValue(json, User.class);
String name = user.getUserName();
return name;
} catch (Exception e) {
e.printStackTrace();
}
return null;
}
访问readjsonasobject,页面输出:
mrbird
- @JsonView
作用在类或者属性上,用来定义一个序列化组。 比如对于User对象,某些情况下只返回userName属性就行,而某些情况下需要返回全部属性。 因此User对象可以定义成如下:
public class User implements Serializable {
private static final long serialVersionUID = 6222176558369919436L;
public interface UserNameView {};
public interface AllUserFieldView extends UserNameView {};
@JsonView(UserNameView.class)
private String userName;
@JsonView(AllUserFieldView.class)
private int age;
@JsonView(AllUserFieldView.class)
private String password;
@JsonView(AllUserFieldView.class)
private Date birthday;
...
}
User定义了两个接口类,一个为userNameView,另外一个为AllUserFieldView继承了userNameView接口。这两个接口代表了两个序列化组的名称。属性userName使用了@JsonView(UserNameView.class),而剩下属性使用了@JsonView(AllUserFieldView.class)。
Spring中Controller方法允许使用@JsonView指定一个组名,被序列化的对象只有在这个组的属性才会被序列化,代码如下:
@JsonView(User.UserNameView.class)
@RequestMapping("getuser")
@ResponseBody
public User getUser() {
User user = new User();
user.setUserName("mrbird");
user.setAge(26);
user.setPassword("123456");
user.setBirthday(new Date());
return user;
}
访问getuser页面输出:
{"userName":"mrbird"}
如果将@JsonView(User.UserNameView.class)替换为@JsonView(User.AllUserFieldView.class),输出:
{"userName":"mrbird","age":26,"password":"123456","birthday":"2018-04-02 11:24:00"}
因为接口AllUserFieldView继承了接口UserNameView所以userName也会被输出。
本文转载于MrBird