Jackson学习笔记

Java下常见的Json类库有Gson、JSON-lib和Jackson等，Jackson相对来说比较高效，在项目中主要使用Jackson进行JSON和Java对象转换，下面给出一些Jackson的JSON操作方法。

一、准备工作

Jackson有1.x系列和2.x系列，2.x系列有3个jar包需要下载：
jackson-core-2.2.3.jar（核心jar包）
jackson-annotations-2.2.3.jar（该包提供Json注解支持）
jackson-databind-2.2.3.jar

一个maven依赖就够了

<dependency><groupId>com.fasterxml.jackson.core</groupId><artifactId>jackson-databind</artifactId><version>2.5.3</version>
</dependency>

import java.util.Date;/*** JSON序列化和反序列化使用的User类*/
public class User {private String name;private Integer age;private Date birthday;private String email;public String getName() {return name;}public void setName(String name) {this.name = name;}public Integer getAge() {return age;}public void setAge(Integer age) {this.age = age;}public Date getBirthday() {return birthday;}public void setBirthday(Date birthday) {this.birthday = birthday;}public String getEmail() {return email;}public void setEmail(String email) {this.email = email;}@Overridepublic String toString() {return "User{" +"name='" + name + '\'' +", age=" + age +", birthday=" + birthday +", email='" + email + '\'' +'}';}
}

二、JAVA对象转JSON[JSON序列化]

import java.io.IOException;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.List;
import com.fasterxml.jackson.databind.ObjectMapper;public class JacksonDemo {public static void main(String[] args) throws ParseException, IOException {User user = new User();user.setName("zhangsan");user.setEmail("zhangsan@163.com");user.setAge(20);SimpleDateFormat dateformat = new SimpleDateFormat("yyyy-MM-dd");user.setBirthday(dateformat.parse("1996-10-01"));/*** ObjectMapper是JSON操作的核心，Jackson的所有JSON操作都是在ObjectMapper中实现。* ObjectMapper有多个JSON序列化的方法，可以把JSON字符串保存File、OutputStream等不同的介质中。* writeValue(File arg0, Object arg1)把arg1转成json序列，并保存到arg0文件中。* writeValue(OutputStream arg0, Object arg1)把arg1转成json序列，并保存到arg0输出流中。* writeValueAsBytes(Object arg0)把arg0转成json序列，并把结果输出成字节数组。* writeValueAsString(Object arg0)把arg0转成json序列，并把结果输出成字符串。*/ObjectMapper mapper = new ObjectMapper();//User类转JSON//输出结果：{"name":"zhangsan","age":20,"birthday":844099200000,"email":"zhangsan@163.com"}String json = mapper.writeValueAsString(user);System.out.println(json);//Java集合转JSON//输出结果：[{"name":"zhangsan","age":20,"birthday":844099200000,"email":"zhangsan@163.com"}]List<User> users = new ArrayList<User>();users.add(user);String jsonlist = mapper.writeValueAsString(users);System.out.println(jsonlist);}
}

三、JSON转Java类[JSON反序列化]

public class JacksonDemo {public static void main(String[] args) throws ParseException, IOException {String json = "{\"name\":\"zhangsan\",\"age\":20,\"birthday\":844099200000,\"email\":\"zhangsan@163.com\"}";/*** ObjectMapper支持从byte[]、File、InputStream、字符串等数据的JSON反序列化。*/ObjectMapper mapper = new ObjectMapper();User user = mapper.readValue(json, User.class);System.out.println(user);}
}

结果

User{name='zhangsan', age=20, birthday=Tue Oct 01 00:00:00 CST 1996, email='zhangsan@163.com'}

public class JacksonDemo {public static ObjectMapper mapper = new ObjectMapper();public static void main(String[] args) throws ParseException, IOException {String json = "[{\"name\":\"zhangsan\",\"age\":20,\"birthday\":844099200000,\"email\":\"zhangsan@163.com\"}]";List<User> beanList = mapper.readValue(json, new TypeReference<List<User>>() {});System.out.println(beanList);}}

结果

[User{name='zhangsan', age=20, birthday=Tue Oct 01 00:00:00 CST 1996, email='zhangsan@163.com'}]

四、JSON注解

Jackson提供了一系列注解，方便对JSON序列化和反序列化进行控制，下面介绍一些常用的注解。
@JsonIgnore 此注解用于属性上，作用是进行JSON操作时忽略该属性。
@JsonFormat 此注解用于属性上，作用是把Date类型直接转化为想要的格式，如@JsonFormat(pattern = "yyyy-MM-dd HH-mm-ss")。
@JsonProperty 此注解用于属性上，作用是把该属性的名称序列化为另外一个名称，如把trueName属性序列化为name，@JsonProperty("name")。

import com.fasterxml.jackson.annotation.JsonFormat;
import com.fasterxml.jackson.annotation.JsonIgnore;
import com.fasterxml.jackson.annotation.JsonProperty;import java.util.Date;/*** JSON序列化和反序列化使用的User类*/
public class User {private String name;//不JSON序列化年龄属性
    @JsonIgnoreprivate Integer age;//格式化日期属性@JsonFormat(pattern = "yyyy年MM月dd日")private Date birthday;//序列化email属性为mail@JsonProperty("my_email")private String email;public String getName() {return name;}public void setName(String name) {this.name = name;}public Integer getAge() {return age;}public void setAge(Integer age) {this.age = age;}public Date getBirthday() {return birthday;}public void setBirthday(Date birthday) {this.birthday = birthday;}public String getEmail() {return email;}public void setEmail(String email) {this.email = email;}@Overridepublic String toString() {return "User{" +"name='" + name + '\'' +", age=" + age +", birthday=" + birthday +", email='" + email + '\'' +'}';}
}

import com.fasterxml.jackson.databind.ObjectMapper;
import java.io.IOException;
import java.text.ParseException;
import java.text.SimpleDateFormat;public class JacksonDemo {public static void main(String[] args) throws ParseException, IOException {User user = new User();user.setName("zhangsan");user.setEmail("zhangsan@163.com");user.setAge(20);SimpleDateFormat dateformat = new SimpleDateFormat("yyyy-MM-dd");user.setBirthday(dateformat.parse("1996-10-01"));ObjectMapper mapper = new ObjectMapper();String json = mapper.writeValueAsString(user);System.out.println(json);}
}

{"name":"zhangsan","birthday":"1996年09月30日","my_email":"zhangsan@163.com"}

 

 

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