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【转载】Java下利用Jackson进行JSON解析和序列化
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参考资料：
https://blog.csdn.net/sdut406/article/details/85647982
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>
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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;
} @Override
public 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
@JsonIgnore
private 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;
} @Override
public 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"}
