Examples of JSON parsing and serialization using Jackson under Java

This article mainly introduces examples of JSON parsing and serialization using Jackson under Java. It has certain reference value. Interested friends can refer to it.

Common Json class libraries under Java include Gson, JSON-lib and Jackson, etc. Jackson is relatively efficient. In the project, Jackson is mainly used to convert JSON and Java objects. Here are some JSON of Jackson How to do it.

1. Preparation

First go to the official website to download the Jackson toolkit. Jackson has 1.x series and 2.x series. As of now, the latest version of the 2.x series is 2.2.3. The 2.x series has 3 jar packages that need to be downloaded:

jackson-core -2.2.3.jar

jackson-annotations-2.2.3.jar

jackson-databind-2.2.3.jar

//JSON序列化和反序列化使用的User类 
import java.util.Date; 
 
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; 
  } 
}

2. Convert JAVA object to JSON [JSON serialization]

import java.io.IOException; 
import java.text.ParseException; 
import java.text.SimpleDateFormat; 
 
import com.fasterxml.jackson.databind.ObjectMapper; 
 
public class JacksonDemo { 
  public static void main(String[] args) throws ParseException, IOException { 
    User user = new User(); 
    user.setName("小民");  
    user.setEmail("xiaomin@sina.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":"小民","age":20,"birthday":844099200000,"email":"xiaomin@sina.com"} 
    String json = mapper.writeValueAsString(user); 
    System.out.println(json); 
     
    //Java集合转JSON 
    //输出结果：[{"name":"小民","age":20,"birthday":844099200000,"email":"xiaomin@sina.com"}] 
    List<User> users = new ArrayList<User>(); 
    users.add(user); 
    String jsonlist = mapper.writeValueAsString(users); 
    System.out.println(jsonlist); 
  } 
}

3. JSON to Java class [JSON deserialization]

import java.io.IOException; 
import java.text.ParseException; 
import com.fasterxml.jackson.databind.ObjectMapper; 
 
public class JacksonDemo { 
  public static void main(String[] args) throws ParseException, IOException { 
    String json = "{\"name\":\"小民\",\"age\":20,\"birthday\":844099200000,\"email\":\"xiaomin@sina.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); 
  } 
}

4. JSON annotations

Jackson provides a series of annotations to facilitate control of JSON serialization and deserialization. Here are some commonly used annotations.

@JsonIgnore This annotation is used on attributes to ignore the attribute when performing JSON operations.

@JsonFormat This annotation is used on attributes. Its function is to directly convert the Date type into the desired format, such as @JsonFormat(pattern = "yyyy-MM-dd HH-mm-ss") .

@JsonProperty This annotation is used on properties. Its function is to serialize the name of the property into another name. For example, the trueName property is serialized into name, @JsonProperty( "name").

import java.util.Date; 
import com.fasterxml.jackson.annotation.*; 
 
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("mail") 
  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; 
  } 
}

import java.io.IOException; 
import java.text.ParseException; 
import java.text.SimpleDateFormat; 
 
import com.fasterxml.jackson.databind.ObjectMapper; 
 
public class JacksonDemo { 
 
  public static void main(String[] args) throws ParseException, IOException { 
    User user = new User(); 
    user.setName("小民");  
    user.setEmail("xiaomin@sina.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); 
    //输出结果：{"name":"小民","birthday":"1996年09月30日","mail":"xiaomin@sina.com"} 
  } 
}

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