一. Gson 是 Google 提供的用来在 Java 对象和 JSON 数据之间进行映射的 Java 类库。可以将一个 JSON 字符串转成一个 Java 对象，或者反过来。

Gson里最重要的对象有2个Gson 和 GsonBuilder。

Gson有2个最基本的方法

1) toJson() – 转换java 对象到JSON

2) fromJson() – 转换JSON到java对象

二. 几个简单的例子。

?exp1（一个简单对象object和json之间的转换）：

public class MsgInfo2 {
	private String message; 
	private String flag;
	public String getMessage() {
		return message;
	}
	public void setMessage(String message) {
		this.message = message;
	}
	public String getFlag() {
		return flag;
	}
	public void setFlag(String flag) {
		this.flag = flag;
	} 
	
}

public class Test1 {

	public static void main(String[] args) {
		MsgInfo2 m2 = new MsgInfo2();
		m2.setFlag("00");
		m2.setMessage("message");
		tojson(m2);
		
		String json = "{'message':'message1','flag':'00'}";
		toObject(json);
	}

	public static void tojson(MsgInfo2 m) {
		// 将对象编译成json
		Gson gson = new Gson();
		String result = gson.toJson(m);
		System.out.println(result);
		// 输出：{"message":"message","flag":"00"}
	}

	public static void toObject(String m) {
		// 将json编译成对象
		Gson gson = new Gson();
		MsgInfo2 msg = gson.fromJson(m, MsgInfo2.class);
		System.out.println(msg.getFlag());//输出:00
		System.out.println(msg.getMessage());//输出：message1
	}
}

?exp2（一个复杂对象object和json之间的转换）：

json的结构如下：

{
????? "org":???? {
????????? "orgId": "orgId",
????????? "orgName": "orgName"
????? },
????? "biz":???? [
????????????????? {
????????????? "appcode": 55,

????????????? "subscode": "subscode0"
????????? },
????????????????? {
????????????? "appcode": 66,
????????????? "subscode": "subscode1"
????????? }
????? ]
??}

public class ComOpen {
	private Org org;
	private List<BizObject> biz;
	public Org getOrg() {
		return org;
	}
	public void setOrg(Org org) {
		this.org = org;
	}
	public List<BizObject> getBiz() {
		return biz;
	}
	public void setBiz(List<BizObject> biz) {
		this.biz = biz;
	}
}

public class Org {
	private String orgId;
	private String orgName;
	public String getOrgId() {
		return orgId;
	}
	public void setOrgId(String orgId) {
		this.orgId = orgId;
	}
	public String getOrgName() {
		return orgName;
	}
	public void setOrgName(String orgName) {
		this.orgName = orgName;
	}
}

public class BizObject {
	private int appcode;
	private String subscode;
	public String getSubscode() {
		return subscode;
	}
	public void setSubscode(String subscode) {
		this.subscode = subscode;
	}
	public int getAppcode() {
		return appcode;
	}
	public void setAppcode(int appcode) {
		this.appcode = appcode;
	}
}

/**
 * 测试java对象和json转换
 *
 * @author yangliang
 * @version 1.0
 * @created 2011-10-11 下午03:14:04
 * @history 
 * @see
 */
public class Test2 {
	public static void main(String[] args) {
		toJson();
		toObject();
	}
	public static void toJson(){
		ComOpen como = new ComOpen();
		Org org = new Org();
		org.setOrgId("orgId");
		org.setOrgName("orgName");
		como.setOrg(org);
		List<BizObject> biz = new ArrayList<BizObject>();
		BizObject bizObject = new BizObject(); 
		bizObject.setAppcode(55);
		bizObject.setSubscode("subscode0");
		BizObject bizObject1 = new BizObject(); 
		bizObject1.setAppcode(66);
		bizObject1.setSubscode("subscode1");
		biz.add(bizObject);
		biz.add(bizObject1);
		como.setBiz(biz);
		Gson gson=new GsonBuilder().create();
		String result = gson.toJson(como);
		System.out.println(result);
		//输出{"org":{"orgId":"orgId","orgName":"orgName"},"biz":接下行
		//[{"appcode":55,"subscode":"subscode0"},{"appcode":66,"subscode":"subscode1"}]}
	}
	
	public static void toObject(){
		String json = "{'org':{'orgId':'orgId','orgName':'orgName'},'biz':" +
		 "[{'appcode':55,'subscode':'subscode0'},{'appcode':66,'subscode':'subscode1'}]}";
		Gson gson=new Gson();
		ComOpen  m3 = gson.fromJson(json, ComOpen.class);
		System.out.println(m3.getBiz().size());