解析json数据的组件-jackson

有关json数据的解析-jackson组件基本用法

Java下常见的Json类库有Gson、JSON-lib和Jackson等，Jackson相对来说比较高效，在项目中主要使用Jackson进行JSON和Java对象转换

一、环境准备
首先去官网下载Jackson工具包，下载地址http://wiki.fasterxml.com/JacksonDownload。Jackson有1.x系列和2.x系列，截止目前2.x系列的最新版本是2.6，2.x系列有3个jar包需要下载：
jackson-core-2.6.0.jar（核心jar包， 下载地址）
https://github.com/FasterXML/jackson-core/wiki
http://repo1.maven.org/maven2/com/fasterxml/jackson/core/jackson-core/2.2.3/jackson-core-2.2.3.jar

jackson-annotations-2.6.0.jar（该包提供Json注解支持， 下载地址）
https://github.com/FasterXML/jackson-annotations/wiki
http://repo1.maven.org/maven2/com/fasterxml/jackson/core/jackson-annotations/2.2.3/jackson-annotations-2.2.3.jar

jackson-databind-2.6.0.jar（ 下载地址）
https://github.com/FasterXML/jackson-databind/wiki
http://repo1.maven.org/maven2/com/fasterxml/jackson/core/jackson-databind/2.2.3/jackson-databind-2.2.3.jar

注：jackson包一定要版本一致

参考地址：http://itindex.net/detail/51074-java-%E5%88%A9%E7%94%A8-jackson

二、测试代码

package com.jackson.test;

import java.io.IOException;
import java.util.Date;

import org.junit.Test;

import com.fasterxml.jackson.core.JsonParseException;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;

public class TestJackson {
    
    /**
     * ObjectMapper中有几种对象转换成JSON数据的方法
     * 1. writeValue(File file, Object obj): 将对象保存到文件中
     * 2. writeValue(OutputStream os, Object obj): 将对象保存到输出流中
     * 3. writeValueAsBytes(Object obj): 将对象保存到字节数组中
     * 3. writeValueAsString(Object obj): 将对象保存到字符串中
     * @throws JsonProcessingException 
     * 
     */
    @Test
    public void m01() throws JsonProcessingException {
        User user = new User();
        user.setUsername("liuyang");
        user.setUserpass("123456");
        user.setUseralias("caleb");
        user.setUserEmail("caleb_520@163.com");
        user.setUserbirthday(new Date());
        ObjectMapper objectMapper = new ObjectMapper(); //ObjectMapper是jackson组件中操作JSON的核心类
        String json = objectMapper.writeValueAsString(user);
        System.out.println("json = " + json);
    }
    
    /**
     * ObjectMapper中将JSON数据转换成Java对象
     * @throws IOException 
     * @throws JsonMappingException 
     * @throws JsonParseException 
     * 
     */
    @Test
    public void m02() throws JsonParseException, JsonMappingException, IOException {
        String json = "{\"username\":\"liuyang\",\"userpass\":\"123456\"}";
        ObjectMapper objectMapper = new ObjectMapper();
        User user = objectMapper.readValue(json, User.class);
        System.out.println("username = " + user.getUsername() + " userpass = " + user.getUserpass());
    }
    
}