Jackson转换java对象与json对象

一、导入jar包：

（因为之前使用的是jackson 1.x的jar包，所以在把json转换成list时候没有objectMapper.getTypeFactory()这个方法，而使用jackson 2.x的jar包会有）

jackson 1.x：jackson-all-1.7.6.jar（1个核心文件）

jackson 2.x：jackson-annotations-2.5.0.jar、jackson-core-2.5.0.jar、jackson-databind-2.5.0.jar（3个核心文件）

二、建立java对象User：

package com.cn.jackson.entity;

public class User {

    private String name;
    
    private Integer age;
    
    private String address;

    public User(){
        
    }
    
    public User(String name, Integer age, String address) {
        super();
        this.name = name;
        this.age = age;
        this.address = address;
    }

    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 String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }
    
    
}

三、测试jackson 2.x的使用方法：

package com.cn.jackson.test;

import java.io.IOException;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import com.cn.jackson.entity.User;
import com.fasterxml.jackson.core.JsonEncoding;
import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.databind.JavaType;
import com.fasterxml.jackson.databind.ObjectMapper;

public class Test_2_x {
    
    public static void main(String[] args) {

        try {
            ObjectMapper objectMapper = new ObjectMapper();
            JsonGenerator jsonGenerator = objectMapper.getJsonFactory()
                    .createJsonGenerator(System.out, JsonEncoding.UTF8);
            
            //对象转JSON
            User user = new User("张三", 23, "深圳市");
            System.out.println("ObjectMapper方式");
            objectMapper.writeValue(System.out, user);//直接输出到控制台
            String userJsonStr = objectMapper.writeValueAsString(user);//返回字符串，输出
            System.out.println(userJsonStr);
            System.out.println("JsonGenerator方式");
            jsonGenerator.writeObject(user);
            System.out.println();
            
            //map转JSON
            Map<String , Object> map = new HashMap<String ,Object>();
            map.put("one", new User("张", 12, "深圳"));
            map.put("two", new User("李", 22, "武汉"));
            map.put("three", new User("王", 32, "北京"));
            System.out.println("ObjectMapper方式");
            objectMapper.writeValue(System.out, map);
            //JsonGenerator方式同上
            
            //list转JSON
            List<User> list = new ArrayList<User>();
            list.add(new User("张", 12, "深圳"));
            list.add(new User("李", 22, "武汉"));
            list.add(new User("王", 32, "北京"));
            System.out.println("ObjectMapper方式");
            objectMapper.writeValue(System.out, list);
            //JsonGenerator方式同上
            
            //JSON转java对象：
            String json = "{\"name\":\"张三\",\"age\":23,\"address\":\"深圳市\"}";
            User zhang = objectMapper.readValue(json, User.class);
            System.out.println(zhang.getName()+"\n"+zhang.getAge()+"\n"+zhang.getAddress());
            
            //JSON转list
            String listJson = "[{\"name\":\"张三\",\"age\":21,\"address\":\"深圳\"},"
                        + "{\"name\":\"李四\",\"age\":11,\"address\":\"武汉\"},"
                        + "{\"name\":\"王五\",\"age\":31,\"address\":\"北京\"}]";
            JavaType javaType1 = objectMapper.getTypeFactory().constructParametricType(ArrayList.class, User.class);
            List<User> userList = (List<User>)objectMapper.readValue(listJson, javaType1);
            for (User user1 : userList) {
                System.out.println(user1.getName()+"\t"+user1.getAge()+"\t"+user1.getAddress());
            }
            
            //JSON转map
            String mapJson = "{\"one\":{\"name\":\"张三\",\"age\":21,\"address\":\"深圳\"},"
                    + "\"two\":{\"name\":\"李四\",\"age\":11,\"address\":\"武汉\"},"
                    + "\"three\":{\"name\":\"王五\",\"age\":31,\"address\":\"北京\"}}";
            JavaType javaType2 = objectMapper.getTypeFactory().constructParametricType(HashMap.class, String.class, User.class);
            Map<String,User> userMap = (Map<String,User>)objectMapper.readValue(mapJson, javaType2);
            User one = userMap.get("one");
            User two = userMap.get("two");
            User three = userMap.get("three");
            System.out.println(one.getName()+"\t"+one.getAge()+"\t"+one.getAddress());
            System.out.println(two.getName()+"\t"+two.getAge()+"\t"+two.getAddress());
            System.out.println(three.getName()+"\t"+three.getAge()+"\t"+three.getAddress());
            
        } catch (IOException e) {
            e.printStackTrace();
        }
    }    
}

四、测试jackson 1.x的使用方法：

package com.cn.jackson.test;

import java.util.List;
import java.util.Map;

import org.codehaus.jackson.map.ObjectMapper;
import org.codehaus.jackson.type.TypeReference;

import com.cn.jackson.entity.User;

public class Test_1_x {

    public static void main(String[] args) {
        try {
            //后面几种转换同Test_2_x一样  //对象转JSON  //map转JSON  //list转JSON  //JSON转java对象
            
            //JSON转list
            ObjectMapper objectMapper = new ObjectMapper();
            String listJson = "[{\"name\":\"张三\",\"age\":21,\"address\":\"深圳\"},"
                    + "{\"name\":\"李四\",\"age\":11,\"address\":\"武汉\"},"
                    + "{\"name\":\"王五\",\"age\":31,\"address\":\"北京\"}]";
            List<User> userList = objectMapper.readValue(listJson, new TypeReference<List<User>>() {});
            for (User user1 : userList) {
                System.out.println(user1.getName()+"\t"+user1.getAge()+"\t"+user1.getAddress());
            }
            
            //JSON转map
            String mapJson = "{\"one\":{\"name\":\"张三\",\"age\":21,\"address\":\"深圳\"},"
                    + "\"two\":{\"name\":\"李四\",\"age\":11,\"address\":\"武汉\"},"
                    + "\"three\":{\"name\":\"王五\",\"age\":31,\"address\":\"北京\"}}";
            Map<String,User> userMap = objectMapper.readValue(mapJson, new TypeReference<Map<String,User>>() {});
            User one = userMap.get("one");
            User two = userMap.get("two");
            User three = userMap.get("three");
            System.out.println(one.getName()+"\t"+one.getAge()+"\t"+one.getAddress());
            System.out.println(two.getName()+"\t"+two.getAge()+"\t"+two.getAddress());
            System.out.println(three.getName()+"\t"+three.getAge()+"\t"+three.getAddress());
        } catch (Exception e) {
            // TODO: handle exception
        }
    }
}