Java对象、Json、Xml转换工具Jackson使用

在Java项目中將一个对象转换成一段Json格式的字符串是非常常见的，能够实现这种需求的工具包也比较多，例如Gson、JSON-lib、Jackson等等。本文主要介绍Jackson的使用，Jackson除了能实现Java对象与Json串的互转外，还能將Java对象转换为Xml格式，使用较为简单而且据说效率比较高。

对于Jackson的jar包我们可以从maven资源库中下载：http://mvnrepository.com/

所需jar包如下，按照名称搜索下载即可。

接下来编写测试用例，我们需要一个java类：

package com.csii.jackson.object;

public class Book{
    private String name;
    private int price;
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getPrice() {
        return price;
    }
    public void setPrice(int price) {
        this.price = price;
    }
    public Book() {

    }
    public Book(String name,int price) {
        this.name = name;
        this.price = price;
    }
    @Override
    public String toString() {
        return "name:" + name +"; price:" + price;
    }

}

1.將Java对象转换为Json字符串：

    @Test
    public void testGenJson()
    {
        ObjectMapper objMapper = new ObjectMapper();
        Book book = new Book("Think in Java",100);
        try {
            jsonGen = objMapper.getJsonFactory().createJsonGenerator(System.out,JsonEncoding.UTF8);
            jsonGen.writeObject(book);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

运行测试方法，控制台输出：

{"name":"Think in Java","price":100}

2.將Json字符串转为Java对象：

    /*
     * Json转Java对象
     */
    @Test
    public void testGenObjByJson()
    {
        ObjectMapper objMapper = new ObjectMapper();
        String json = "{\"name\":\"Think in Java\",\"price\":100}";
        try {
            Book book = objMapper.readValue(json, Book.class);
            System.out.println(book);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

由于我们重写了Book类的toString方法，运行测试方法，控制台输出：

name:Think in Java; price:100

3.將Java对象转为Xml格式：

     /*
     * Java对象转xml
     */
    @Test
    public void testGenXml()
    {
        XmlMapper xmlMapper = new XmlMapper();

        Book book = new Book("Think in Java",100);
        try {
            String xmlStr =  xmlMapper.writeValueAsString(book);
            System.out.println(xmlStr);
        } catch (JsonProcessingException e) {
            e.printStackTrace();
        }
    }

运行测试方法，控制台输出：

<Book xmlns=""><name>Think in Java</name><price>100</price></Book>

4.將xml格式字符串转为Java对象：

    /*
     * xml转Java对象
     */
    @Test
    public void testGenObjByXml()
    {
        XmlMapper xmlMapper = new XmlMapper();
        String xmlStr = "<Book><name>Think in Java</name><price>100</price></Book>";
        try {
            Book book = xmlMapper.readValue(xmlStr, Book.class);
            System.out.println(book);
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

    }

输出内容：

name:Think in Java; price:100

完整的测试用例代码：

package com.csii.jackson.test;

import java.io.IOException;

import org.junit.Test;

import com.csii.jackson.object.Book;
import com.fasterxml.jackson.core.JsonEncoding;
import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.dataformat.xml.XmlMapper;
@SuppressWarnings("deprecation")
public class JsonTest {
    private JsonGenerator jsonGen = null;
    /*
     * Java对象转 Json
     */
    @Test
    public void testGenJson()
    {
        ObjectMapper objMapper = new ObjectMapper();
        Book book = new Book("Think in Java",100);
        try {
            jsonGen = objMapper.getJsonFactory().createJsonGenerator(System.out,JsonEncoding.UTF8);
            jsonGen.writeObject(book);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    /*
     * Json转Java对象
     */
    @Test
    public void testGenObjByJson()
    {
        ObjectMapper objMapper = new ObjectMapper();
        String json = "{\"name\":\"Think in Java\",\"price\":100}";
        try {
            Book book = objMapper.readValue(json, Book.class);
            System.out.println(book);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    /*
     * Java对象转xml
     */
    @Test
    public void testGenXml()
    {
        XmlMapper xmlMapper = new XmlMapper();

        Book book = new Book("Think in Java",100);
        try {
            String xmlStr =  xmlMapper.writeValueAsString(book);
            System.out.println(xmlStr);
        } catch (JsonProcessingException e) {
            e.printStackTrace();
        }
    }
    /*
     * xml转Java对象
     */
    @Test
    public void testGenObjByXml()
    {
        XmlMapper xmlMapper = new XmlMapper();
        String xmlStr = "<Book><name>Think in Java</name><price>100</price></Book>";
        try {
            Book book = xmlMapper.readValue(xmlStr, Book.class);
            System.out.println(book);
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

    }
}