反射机制：getDeclaredField和getField的区别

在做后台开发时实体的固定字段一般会抽取为一个父类，其他类继承该父类，例如主键字段，会放到一个父类中（IdEntity），其他类继承该类，但是我们在操作时操作的是子类，在通过子类获取父类属性是getDeclaredField和getField是不一样的，简单说

1. getDeclaredFiled 仅能获取类本身的属性成员（包括私有、共有、保护） 
2. getField 仅能获取类(及其父类可以自己测试) public属性成员

因此在获取父类的私有属性时，要通过getSuperclass的之后再通过getDeclaredFiled获取。

父类，出去id作为父类字段

import javax.persistence.Column;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.MappedSuperclass;

import org.hibernate.annotations.GenericGenerator;
@MappedSuperclass
public abstract class IdEntity {
	private String id;

	@Id
	@GeneratedValue(generator = "paymentableGenerator")
	@GenericGenerator(name = "paymentableGenerator", strategy = "uuid")
	@Column(name ="ID",nullable=false,length=32)
	public String getId() {
		return id;
	}

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

}

子类

public class Reflect extends IdEntity {

	public String publicField;
	private String privateField;

	public Reflect(String publicField, String privateField) {
		super();
		this.publicField = publicField;
		this.privateField = privateField;
	}

	public String getPrivateField() {
		return privateField;
	}

	public void setPrivateField(String privateField) {
		this.privateField = privateField;
	}

}

测试类：

import java.lang.reflect.Field;

public class ReflectDemo {

	/**
	 * @Description: TODO
	 * @param @param args
	 * @return void
	 * @throws SecurityException
	 * @throws NoSuchFieldException
	 * @throws IllegalAccessException
	 * @throws IllegalArgumentException
	 * @throws
	 * @author ydecai
	 * @date 2019-1-23
	 */
	public static void main(String[] args) throws NoSuchFieldException, SecurityException, IllegalArgumentException, IllegalAccessException {
		Reflect re = new Reflect("zhangsan", "lisi");
		re.setId("111");
		//getDeclaredFiled获取本类属性
//		Field publicField = re.getClass().getDeclaredField("publicField");
//		System.out.println(publicField.get(re));
		Field publicField = re.getClass().getField("publicField");
		System.out.println(publicField.get(re));
		//getField获取公有属性，包括父类的，下面语句报错
		//Field privateField = re.getClass().getField("privateField");
		Field privateField = re.getClass().getDeclaredField("privateField");
		privateField.setAccessible(true);
		System.out.println(privateField.get(re));
		//获取父类私有属性并获取值
		Field fileId = re.getClass().getSuperclass().getDeclaredField("id");
		fileId.setAccessible(true);
		System.out.println(fileId.get(re));
	}

}