json字符串与Object对象间的转换

Jackson可以轻松的将Java对象转换成json对象和xml文档，同样也可以将json、xml转换成Java对象。功能非常的强悍！

1.maven导入jar包

	    com.fasterxml.jackson.core
	    jackson-databind
	    2.8.6

这样就导入了jackson的三个jar包

jackson-databind-2.8.6.jar，jackson-core-2.8.6.jar，jackson-annotations-2.8.6.jar

2.用objectMapper.writeValueAsString(object)，把 Object对象转换成json字符串

/**
 * Object转换成json字符串
 * @author Administrator
 *
 */
public class Test1 {
	public static void main(String[] args) throws Exception{
		Student st = new Student();
		st.setAge("23");
		st.setName("Lucy");
		ObjectMapper mapper = new ObjectMapper();
		String aa = mapper.writeValueAsString(st);
		System.out.println(aa);
		
		Teacher t = new Teacher();
		t.setId("223");
		User u = new User();
		u.setId("33");
		u.setName("Mark");
		t.setUser(u);
		String b = mapper.writeValueAsString(t);
		System.out.println(b);
	}

输出

{"name":"Lucy","age":"23"}
{"id":"223","user":{"id":"33","name":"Mark"}}

把java对象转换成了json字符串，就用了 objectMapper. writeValueAsString(object) 这样一个方法，很简单方便。

3.用objectMapper.readValue(byte[] src, Class valueType);把json字符串转换成java对象

也可以用objectMapper.readValue(String content, Class valueType);转换成byte[]，可以预防乱码之类的。

/**
 * json装换成Object对象或其他bean
 * @author Administrator
 *
 */
public class Test2 {

	public static void main(String[] args) throws JsonParseException, JsonMappingException, IOException {
		ObjectMapper ma = new ObjectMapper();
		String a = "{\"id\":\"223\",\"user\":{\"id\":\"33\",\"name\":\"Mark\"}}";
		Object o = ma.readValue(a, Object.class);
		System.out.println(o);
		String b = "{\"id\":\"223\",\"user\":{\"id\":\"33\",\"name\":\"张小花\"}}";
		Teacher th = ma.readValue(b.getBytes("UTF-8"), Teacher.class);
		System.out.println(th);
	}
}