反射详解

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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
}