1.Maven Dependency
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion> <groupId>org.fool.jackson</groupId> <artifactId>Jackson</artifactId> <version>0.0.1-SNAPSHOT</version> <packaging>jar</packaging> <name>Jackson</name> <url>http://maven.apache.org</url> <properties> <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding> </properties> <dependencies> <dependency> <groupId>com.fasterxml.jackson.core</groupId> <artifactId>jackson-databind</artifactId> <version>2.1.3</version> </dependency> <dependency> <groupId>org.apache.commons</groupId> <artifactId>commons-lang3</artifactId> <version>3.1</version> </dependency> <dependency> <groupId>junit</groupId> <artifactId>junit</artifactId> <version>4.11</version> <scope>test</scope> </dependency> </dependencies> </project>
2.Project Directory
3.User.java
package org.fool.jackson;
import java.util.List;
import org.apache.commons.lang3.builder.ToStringBuilder;
import org.apache.commons.lang3.builder.ToStringStyle;
public class User
{
private String name;
private int age;
private List<String> msgs;
public User()
{
}
public User(String name, int age, List<String> msgs)
{
this.name = name;
this.age = age;
this.msgs = msgs;
}
public String getName()
{
return name;
}
public void setName(String name)
{
this.name = name;
}
public int getAge()
{
return age;
}
public void setAge(int age)
{
this.age = age;
}
public List<String> getMsgs()
{
return msgs;
}
public void setMsgs(List<String> msgs)
{
this.msgs = msgs;
}
@Override
public String toString()
{
return ToStringBuilder.reflectionToString(this,
ToStringStyle.SHORT_PREFIX_STYLE);
}
}
4.Java Object To Json
Convert an “user” object into JSON formatted string, and save it into a file “user.json“.
package org.fool.jackson;
import java.io.File;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import com.fasterxml.jackson.core.JsonGenerationException;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;
public class JavaObjectToJson
{
public static void main(String[] args)
{
List<String> msgs = new ArrayList<>();
msgs.add("msg1");
msgs.add("msg2");
msgs.add("msg3");
User user = new User("Hero", 30, msgs);
ObjectMapper mapper = new ObjectMapper();
try
{
// convert user object to json string, and save to a file
mapper.writeValue(new File("user.json"), user);
// display to console
System.out.println(mapper.writeValueAsString(user));
// this is Jackson 1.x API only
// System.out.println(mapper.defaultPrettyPrintingWriter()
// .writeValueAsString(user));
// for Jackson 2.x use the line below instead of the one
System.out.println(mapper.writer().withDefaultPrettyPrinter()
.writeValueAsString(user));
}
catch (JsonGenerationException e)
{
e.printStackTrace();
}
catch (JsonMappingException e)
{
e.printStackTrace();
}
catch (JsonProcessingException e)
{
e.printStackTrace();
}
catch (IOException e)
{
e.printStackTrace();
}
}
}
结果 — JavaObjectToJson
从图中可以看出,下面的JSON格式输出更加pretty,但是Jackson1.x和Jackson2.x的Pretty Print的API是不一样的
Jackson 1.x的Pretty Print 采用如下格式
System.out.println(mapper.defaultPrettyPrintingWriter().writeValueAsString(user));
Jackson 2.x的Pretty Print 采用如下格式
System.out.println(mapper.writer().withDefaultPrettyPrinter().writeValueAsString(user));
我这里由于使用的是Jackson 2.x的API,所以采用下面一种方法。
5.Json To Java Object
Read JSON string from file “user.json“, and convert it back to Java object.
package org.fool.jackson;
import java.io.File;
import java.io.IOException;
import com.fasterxml.jackson.core.JsonParseException;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;
public class JsonToJavaObject
{
public static void main(String[] args)
{
ObjectMapper mapper = new ObjectMapper();
try
{
// read from file, convert it to user class
User user = mapper.readValue(new File("user.json"), User.class);
// display to console
System.out.println(user);
}
catch (JsonParseException e)
{
e.printStackTrace();
}
catch (JsonMappingException e)
{
e.printStackTrace();
}
catch (IOException e)
{
e.printStackTrace();
}
}
}
结果 — JsonToJavaObject