Jackson解析JSON例子

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本文介绍如何使用Jackson库进行Java对象与JSON之间的转换，包括单个实体、列表、地图及复杂类型的序列化与反序列化。

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

工程中JavaObjectToJson.java 和 JsonToJavaObject.java，在Jackson Basic(http://agilestyle.iteye.com/blog/1779257)中已列举，这里不再赘述。

3.POJO

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.JUnit Test

JacksonTest.java基本框架如下

package org.fool.jackson;

import java.io.File;
import java.io.IOException;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;

import org.junit.After;
import org.junit.Before;
import org.junit.Test;

import com.fasterxml.jackson.core.JsonEncoding;
import com.fasterxml.jackson.core.JsonGenerationException;
import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.core.JsonParseException;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.node.JsonNodeFactory;

public class JacksonTest
{
	private JsonGenerator jsonGenerator = null;
	private ObjectMapper objectMapper = null;
	private User user = null;

	@Before
	public void setUp()
	{
		List<String> msgs = new ArrayList<>();
		msgs.add("msg1");
		msgs.add("msg2");
		msgs.add("msg3");

		user = new User("Hero", 30, msgs);

		objectMapper = new ObjectMapper();

		try
		{
			jsonGenerator = objectMapper.getFactory().createJsonGenerator(
					System.out, JsonEncoding.UTF8);
		}
		catch (IOException e)
		{
			e.printStackTrace();
		}
	}

	@After
	public void tearDown()
	{
		try
		{
			if (jsonGenerator != null)
			{
				jsonGenerator.flush();
			}

			if (!jsonGenerator.isClosed())
			{
				jsonGenerator.close();
			}
		}
		catch (IOException e)
		{
			e.printStackTrace();
		}
	}
        ......
}

writeEntity2Json

...
    @Test
	public void writeEntity2Json()
	{
		try
		{
			System.out.println("jsonGenerator");
			jsonGenerator.writeObject(user);
			System.out.println();

			System.out.println("objectMapper");
			objectMapper.writeValue(new File("Entity2Json.json"), user);
			objectMapper.writeValue(System.out, user);
		}
		catch (JsonGenerationException e)
		{
			e.printStackTrace();
		}
		catch (JsonMappingException e)
		{
			e.printStackTrace();
		}
		catch (JsonProcessingException e)
		{
			e.printStackTrace();
		}
		catch (IOException e)
		{
			e.printStackTrace();
		}
	}
...

result

jsonGenerator
{"name":"Hero","age":30,"msgs":["msg1","msg2","msg3"]}
objectMapper
{"name":"Hero","age":30,"msgs":["msg1","msg2","msg3"]}

writeList2Json

...        
    @Test
	public void writeList2Json()
	{
		List<User> list = new ArrayList<>();
		list.add(user);

		try
		{
			System.out.println("jsonGenerator");
			jsonGenerator.writeObject(list);
			System.out.println();

			System.out.println("objectMapper");
			objectMapper.writeValue(new File("List2Json.json"), list);
			objectMapper.writeValue(System.out, list);
		}
		catch (JsonGenerationException e)
		{
			e.printStackTrace();
		}
		catch (JsonMappingException e)
		{
			e.printStackTrace();
		}
		catch (JsonProcessingException e)
		{
			e.printStackTrace();
		}
		catch (IOException e)
		{
			e.printStackTrace();
		}
	}
...

result

jsonGenerator
[{"name":"Hero","age":30,"msgs":["msg1","msg2","msg3"]}]
objectMapper
[{"name":"Hero","age":30,"msgs":["msg1","msg2","msg3"]}]

writeMap2Json

...
    @Test
	public void writeMap2Json()
	{
		Map<String, Object> map = new HashMap<>();
		map.put("name", user.getName());
		map.put("age", user.getAge());
		map.put("msg", user.getMsgs());
		map.put("user", user);

		try
		{
			System.out.println("jsonGenerator");
			jsonGenerator.writeObject(map);
			System.out.println();

			System.out.println("objectMapper");
			objectMapper.writeValue(new File("Map2Json.json"), map);
			objectMapper.writeValue(System.out, map);
		}
		catch (JsonGenerationException e)
		{
			e.printStackTrace();
		}
		catch (JsonMappingException e)
		{
			e.printStackTrace();
		}
		catch (JsonProcessingException e)
		{
			e.printStackTrace();
		}
		catch (IOException e)
		{
			e.printStackTrace();
		}
	}
...

result

jsonGenerator
{"age":30,"name":"Hero","user":{"name":"Hero","age":30,"msgs":["msg1","msg2","msg3"]},"msg":["msg1","msg2","msg3"]}
objectMapper
{"age":30,"name":"Hero","user":{"name":"Hero","age":30,"msgs":["msg1","msg2","msg3"]},"msg":["msg1","msg2","msg3"]}

writeOthers2JSON

...
    @Test
	public void writeOthers2JSON()
	{
		try
		{
			String str = "hello world";
			jsonGenerator.writeBinary(str.getBytes()); // byte
			jsonGenerator.writeBoolean(true); // boolean
			jsonGenerator.writeNull(); // null
			jsonGenerator.writeNumber(8.8f); // float
			jsonGenerator.writeRaw("c"); // char
			jsonGenerator.writeRaw(str, 1, 6); // String
			jsonGenerator.writeRawValue(str, 1, 6); // String
			jsonGenerator.writeString(str); // String
			jsonGenerator.writeTree(JsonNodeFactory.instance.POJONode(str));
			System.out.println();

			jsonGenerator.writeStartObject(); // {
			jsonGenerator.writeObjectFieldStart("user"); // user:{
			jsonGenerator.writeStringField("name", "Hero"); // name:Hero
			jsonGenerator.writeNumberField("age", 30); // age:30
			jsonGenerator.writeBooleanField("isMarried", true); // isMarried:true
			jsonGenerator.writeEndObject(); // }

			jsonGenerator.writeArrayFieldStart("infos"); // infos:[
			jsonGenerator.writeNumber(8.8f); // 8.8
			jsonGenerator.writeString("this is an array"); // this is an array
			jsonGenerator.writeEndArray(); // ]

			jsonGenerator.writeEndObject(); // }

			String[] arrs = { "hello", "world", "Jackson" };
			jsonGenerator.writeStartObject(); // {
			jsonGenerator.writeObjectField("user", user); // user:{bean}
			jsonGenerator.writeObjectField("infos", arrs); // infos:[array]
			jsonGenerator.writeEndObject(); // }
		}
		catch (JsonGenerationException e)
		{
			e.printStackTrace();
		}
		catch (IOException e)
		{
			e.printStackTrace();
		}
	}
...

result

"aGVsbG8gd29ybGQ=" true null 8.8cello w ello w "hello world" "hello world"
 {"user":{"name":"Hero","age":30,"isMarried":true},"infos":[8.8,"this is an array"]} {"user":{"name":"Hero","age":30,"msgs":["msg1","msg2","msg3"]},"infos":["hello","world","Jackson"]}

readJson2Entity

...
    @Test
	public void readJson2Entity()
	{
		try
		{
			User user = objectMapper.readValue(new File("Entity2Json.json"),
					User.class);
			System.out.println(user.getName());
			System.out.println(user);
		}
		catch (JsonParseException e)
		{
			e.printStackTrace();
		}
		catch (JsonMappingException e)
		{
			e.printStackTrace();
		}
		catch (IOException e)
		{
			e.printStackTrace();
		}
	}
...

result

Hero
User[name=Hero,age=30,msgs=[msg1, msg2, msg3]]

readJson2List

...
    @Test
	public void readJson2List()
	{
		try
		{
			@SuppressWarnings("unchecked")
			List<LinkedHashMap<String, Object>> list = objectMapper.readValue(
					new File("List2Json.json"), List.class);

			System.out.println(list.size());

			for (LinkedHashMap<String, Object> map : list)
			{
				Set<Entry<String, Object>> set = map.entrySet();
				for (Iterator<Entry<String, Object>> iterator = set.iterator(); iterator
						.hasNext();)
				{
					Map.Entry<String, Object> entry = iterator.next();
					String key = entry.getKey();
					Object value = entry.getValue();

					System.out.println(key + ":" + value);
				}
			}
		}
		catch (JsonParseException e)
		{
			e.printStackTrace();
		}
		catch (JsonMappingException e)
		{
			e.printStackTrace();
		}
		catch (IOException e)
		{
			e.printStackTrace();
		}
	}
...

result

1
name:Hero
age:30
msgs:[msg1, msg2, msg3]

readJson2Map

...
    @Test
	public void readJson2Map()
	{
		try
		{
			@SuppressWarnings("unchecked")
			Map<String, Map<String, Object>> map = objectMapper.readValue(
					new File("Map2Json.json"), Map.class);

			System.out.println(map.size());

			Set<String> set = map.keySet();
			for (Iterator<String> iterator = set.iterator(); iterator.hasNext();)
			{
				String key = iterator.next();
				Object value = map.get(key);

				System.out.println(key + ":" + value);
			}
		}
		catch (JsonParseException e)
		{
			e.printStackTrace();
		}
		catch (JsonMappingException e)
		{
			e.printStackTrace();
		}
		catch (IOException e)
		{
			e.printStackTrace();
		}
	}
...

result

4
age:30
name:Hero
user:{name=Hero, age=30, msgs=[msg1, msg2, msg3]}
msg:[msg1, msg2, msg3]

readJson2Array

...
    @Test
	public void readJson2Array()
	{
		try
		{
			User[] users = objectMapper.readValue(new File("List2Json.json"),
					User[].class);
			for (User user : users)
			{
				System.out.println(user);
			}
		}
		catch (JsonParseException e)
		{
			e.printStackTrace();
		}
		catch (JsonMappingException e)
		{
			e.printStackTrace();
		}
		catch (IOException e)
		{
			e.printStackTrace();
		}
	}
...

result

User[name=Hero,age=30,msgs=[msg1, msg2, msg3]]