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反射详解

前言

学习框架底层必须要掌握反射。

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public class Person {
/** 属性 */
private String name;
private int age;

/** 构造器 */
public Person(){ }
public Person(String name, int age) {
this.name = name;
this.age = age;
}

/** getter And Setter */
}

获取类对象的三种方法

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@Test
public void testClass() throws ClassNotFoundException {
Class c1 = Person.class;
Class c2 = new Person().getClass();
Class c3 = Class.forName("com.ahao.javaeeDemo.Person");
System.out.print(c1+"\n"+c2+"\n"+c3);
}

通过反射创建对象

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@Test
public void testNew() throws ClassNotFoundException,
IllegalAccessException, InstantiationException,
NoSuchMethodException, InvocationTargetException {
Class clazz = Class.forName("com.ahao.javaeeDemo.Person");
Person p1 = (Person) clazz.newInstance();
System.out.println("无参构造方法:"+p1.toString());
Person p2 = (Person) clazz.getConstructor(String.class, int.class).newInstance("张三", 12);
System.out.println("有参构造方法:"+p2.toString());
}

操作Field

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@Test
public void testField() throws ClassNotFoundException,
NoSuchFieldException,
IllegalAccessException, InstantiationException {
Class clazz = Class.forName("com.ahao.javaeeDemo.Person");
Person p1 = (Person) clazz.newInstance();

Field name = clazz.getDeclaredField("name");//获取一个自己声明的Field,要访问父类Field要用getField()
name.setAccessible(true);//默认只能操作public,如果要操作其他权限,需要使用这个方法
name.set(p1, "张三");//相当于p1.name = "张三"
System.out.println(p1.toString());
}

操作Method

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@Test
public void testMethod() throws ClassNotFoundException,
IllegalAccessException, InstantiationException,
NoSuchMethodException, InvocationTargetException {
Class clazz = Class.forName("com.ahao.javaeeDemo.Person");
Person p1 = (Person) clazz.newInstance();

Method method = clazz.getDeclaredMethod("setName", String.class);//获取一个自己声明的Method,要访问父类Field要用getMethod()
method.setAccessible(true);//默认只能操作public,如果要操作其他权限,需要使用这个方法
method.invoke(p1, "张三");//相当于p1.setName("张三")
System.out.println(p1.toString());
//method.invoke(null, args);//当对象为null时,操作static方法
}
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