json跟Bean转换抛异常JSONException,NoSuchMethodException

采用json-lib-2.4-jdk15.jar把json转化为vo类的时候抛异常，异常信息如下：

net.sf.json.JSONException: java.lang.NoSuchMethodException: Property 'id' has no setter method in class 'class org.research.json.Student'
	at net.sf.json.util.PropertySetStrategy$DefaultPropertySetStrategy._setProperty(PropertySetStrategy.java:69)
	at net.sf.json.util.PropertySetStrategy$DefaultPropertySetStrategy.setProperty(PropertySetStrategy.java:60)
	at net.sf.json.JSONObject.setProperty(JSONObject.java:1394)
	at net.sf.json.JSONObject.toBean(JSONObject.java:366)
	at net.sf.json.JSONObject.toBean(JSONObject.java:233)

 原因是vo类不是public的，错误代码如下：

public class TestJson {
	public static void main(String[] args) {
		Map<String, Class<String>> classMap = new HashMap<String, Class<String>>();
		classMap.put("id", String.class);
		classMap.put("name", String.class);
		String content = "{ \"id\": \"Elliotte\", \"name\":\"Harold\" }";
		Student vo = new Student();
		try {
			vo = (Student) JSONObject.toBean(JSONObject.fromObject(content), Student.class);
			System.out.println("**Student:" + vo);
		} catch (Exception e) {
			e.printStackTrace();
		}

	}

}
class Student {
	private String id;
	private String name;
	 
	public String getId() {
    	return id;
    }

	public void setId(String id) {
    	this.id = id;
    }

	public String getName() {
    	return name;
    }

	public void setName(String name) {
    	this.name = name;
    }

	@Override
    public String toString() {
	    return "Student [id=" + id + ", name=" + name + "]";
    }
}

 正确的做法是vo类为非public，产生错误的原因，看java的反射，lib中操作vo属性是调用的是如下代码：

 Field field = bean.getClass().getField( key );
 if( field != null ){
       field.set( bean, value );
 }