Java下常見的Json類庫有Gson、JSON-lib和Jackson等,Jackson相對來說比較高效,在項目中主要使用Jackson進行JSON和Java對象轉換,下面給出一些Jackson的JSON操作方法。
一、準備工作
Jackson有1.x系列和2.x系列,2.x系列有3個jar包需要下載:
jackson-core-2.2.3.jar(核心jar包)
jackson-annotations-2.2.3.jar(該包提供Json註解支持)
jackson-databind-2.2.3.jar
一個maven依賴就夠了
<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類
*/
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對象轉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("[email protected]");
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中實現。
* ObjectMapper有多個JSON序列化的方法,可以把JSON字符串保存File、OutputStream等不同的介質中。
* writeValue(File arg0, Object arg1)把arg1轉成json序列,並保存到arg0文件中。
* writeValue(OutputStream arg0, Object arg1)把arg1轉成json序列,並保存到arg0輸出流中。
* writeValueAsBytes(Object arg0)把arg0轉成json序列,並把結果輸出成字節數組。
* writeValueAsString(Object arg0)把arg0轉成json序列,並把結果輸出成字符串。
*/
ObjectMapper mapper = new ObjectMapper();
//User類轉JSON
//輸出結果:{"name":"zhangsan","age":20,"birthday":844099200000,"email":"[email protected]"}
String json = mapper.writeValueAsString(user);
System.out.println(json);
//Java集合轉JSON
//輸出結果:[{"name":"zhangsan","age":20,"birthday":844099200000,"email":"[email protected]"}]
List<User> users = new ArrayList<User>();
users.add(user);
String jsonlist = mapper.writeValueAsString(users);
System.out.println(jsonlist);
}
}
三、JSON轉Java類[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\":\"[email protected]\"}";
/**
* ObjectMapper支持從byte[]、File、InputStream、字符串等數據的JSON反序列化。
*/
ObjectMapper mapper = new ObjectMapper();
User user = mapper.readValue(json, User.class);
System.out.println(user);
}
}
結果
User{name='zhangsan', age=20, birthday=Tue Oct 01 00:00:00 CST 1996, email='[email protected]'}
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\":\"[email protected]\"}]";
List<User> beanList = mapper.readValue(json, new TypeReference<List<User>>() {});
System.out.println(beanList);
}
}
結果
[User{name='zhangsan', age=20, birthday=Tue Oct 01 00:00:00 CST 1996, email='[email protected]'}]
四、JSON註解
Jackson提供了一系列註解,方便對JSON序列化和反序列化進行控制,下面介紹一些常用的註解。
@JsonIgnore 此註解用於屬性上,作用是進行JSON操作時忽略該屬性。
@JsonFormat 此註解用於屬性上,作用是把Date類型直接轉化爲想要的格式,如@JsonFormat(pattern = "yyyy-MM-dd HH-mm-ss")。
@JsonProperty 此註解用於屬性上,作用是把該屬性的名稱序列化爲另外一個名稱,如把trueName屬性序列化爲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類
*/
public class User {
private String name;
//不JSON序列化年齡屬性
@JsonIgnore
private Integer age;
//格式化日期屬性
@JsonFormat(pattern = "yyyy年MM月dd日")
private Date birthday;
//序列化email屬性爲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("[email protected]");
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":"[email protected]"}