java 反射机制获取类名、属性、方法、构造器和反射动态使用

被反射的类:

@Table("tb_student")
public class Student {

    @Fields(columnName="id",type="int",length=10)
    private int id;

    @Fields(columnName="studentName",type="varchar",length=10)
    private String studentName;

    @Fields(columnName="age",type="int",length=3)
    private int age;

    public int getId() {
            return id;
    }
    public void setId(int id) {
            this.id = id;
    }
    public String getStudentName() {
            return studentName;
    }
    public void setStudentName(String studentName) {
            this.studentName = studentName;
    }
    public int getAge() {
            return age;
    }
    public void setAge(int age) {
            this.age = age;
    }
    public Student(int id, String studentName, int age) {
        super();
        this.id = id;
        this.studentName = studentName;
        this.age = age;
    }

    public Student() {

    }

反射获取类的信息:

@SuppressWarnings("all") //压制警告
public class Deam {

public static void main(String[] args) throws NoSuchFieldException, SecurityException, NoSuchMethodException {

    Class c;
    try {
        c = Class.forName("cn.sxt.in.Student");
        //获取类名
        System.out.println(c.getName());  //获取包名+类名
        System.out.println(c.getSimpleName()); //只获取类名

        //获取属性
        Field[] fields=c.getFields();   //返回属性数组,只能获取公开属性
        System.out.println(fields.length);

        Field[] fields2=c.getDeclaredFields(); //获得所有类型的属性

        for(Field e:fields2)
        {
            System.out.println("aa");
            System.out.println(e);
        }

        System.out.println(fields2.length);

        Field f=c.getDeclaredField("studentName");
        System.out.println(f);

        //获取方法

        Method[] method =c.getMethods();  //获取公开方法
        Method[] method2=c.getDeclaredMethods();  //获取所有方法
        for(Method mm:method2)
        {
            System.out.println(mm);
        }

        Method m=c.getDeclaredMethod("getStudentName", null); //第二个为参数类型，没有为null
        Method m2=c.getDeclaredMethod("setStudentName", String.class); //方法的参数类型是String
        //获取构造器
        Constructor[] co=c.getDeclaredConstructors();
        for(Constructor cc:co)
        {
            System.out.println(cc);
        }

        Constructor coo=c.getDeclaredConstructor(null);  //获取无参构造器
        System.out.println(coo);  
        Constructor coo2=c.getDeclaredConstructor(int.class,String.class,int.class);//获取指定有参构造器
        System.out.println(coo2);  
    } catch (ClassNotFoundException e) {
        e.printStackTrace();
    }

}

}
}

通过反射动态操作方法属性:

public class play {

public static void main(String[] args) throws NoSuchMethodException, SecurityException, InstantiationException, IllegalAccessException, IllegalArgumentException, InvocationTargetException, NoSuchFieldException
{
    try {
        Class c=Class.forName("cn.sxt.in.Student");
        //Class<Student> c=(Class<Student>)Class.forName("cn.sxt.in.Student");后面操作不用强转

        //通过反射调用构造方法，构造对象
        Student s=(Student)c.newInstance();  //实际上调用了User的无参构造方法
        System.out.println(s);

        //指定构造对象
        Constructor<Student> cc=c.getDeclaredConstructor(int.class,String.class,int.class); //获得构造器方法
        Student s2=cc.newInstance(001,"me",19);    //传入实际参数生成对象
        System.out.println(s2.getStudentName());

        //反射调用普通方法
        Student s3=(Student) c.newInstance();
        Method method=c.getDeclaredMethod("setStudentName", String.class);
        method.invoke(s3, "mee");  //激活方法,第一个参数为对象，第二个参数为传入信息,相当于s3.setStudentName(String s);
        System.out.println(s3.getStudentName());

        //通过反射操作属性
        Student s4=(Student)c.newInstance();
        Field f=c.getDeclaredField("studentName"); //获得属性
    //  f.set(s4,"yyy"); //设置属性信息，第一个参数为设定的对象，第二个为实际信息，相当于s4.set(String s);
    //  System.out.println(s4.getStudentName()); //因为是私有属性，不能直接调用

        //访问私有属性
        Student s5=(Student) c.newInstance();

        Field ff=c.getDeclaredField("studentName");
        ff.setAccessible(true); //不需安全检查，可直接访问私有属性，其他类型也有该方法(类等)
        ff.set(s5, "ada");
        System.out.println(s5.getStudentName());
        System.out.println(ff.get(s5)); //直接通过属性对象调用

    } catch (ClassNotFoundException e) {

        e.printStackTrace();
    }
}
}