Java Advanced - Reflection & Dynamic Proxy Detailed Explanation

//The static method forName in this class//("Full class name of class"): Full class name = Package name + Class nameClass clazz1 = ("");
//Source code stage acquisition --- First load the Student into memory, and then obtain the object of the bytecode file//clazz represents the bytecode file object of the Student class.//It is the bytecode file object generated after this file is loaded into memory​
​
//2. Get through class attribute//Class name.classClass clazz2 = ;
​
//Because the class file is unique in the hard disk, the object generated after this file is loaded into memory is also unique(clazz1 == clazz2);//true
​
​
//3. Obtain the bytecode file object through the Student objectStudent s = new Student();
Class clazz3 = ();
(clazz1 == clazz2);//true
(clazz2 == clazz3);//true

public class ReflectDemo2 {
    public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException {
        //1. Obtain the whole (class bytecode file object)        Class clazz = ("");
​
​
        //2. Get the constructor object        //Get all constructors (public)        Constructor[] constructors1 = ();
        for (Constructor constructor : constructors1) {
            (constructor);
        }
​
        ("=======================");
​
        //Get all constructs (with private ones)        Constructor[] constructors2 = ();
​
        for (Constructor constructor : constructors2) {
            (constructor);
        }
        ("=======================");
​
        //Get the specified empty parameter structure        Constructor con1 = ();
        (con1);
​
        Constructor con2 = (,);
        (con2);
​
        ("=======================");
        //Get the specified construct (all constructs can be obtained, including public and private)        Constructor con3 = ();
        (con3);
        //Understanding (con3 == con1);        //Every time you get the constructor object, a new one will be new.​
        Constructor con4 = ();
        (con4);
    }
}

//First of all, there must be a javabean classpublic class Student {
    private String name;
​
    private int age;
​
​
    public Student() {
​
    }
​
    public Student(String name) {
         = name;
    }
​
    private Student(String name, int age) {
         = name;
         = age;
    }
​
​
    /**
      * Get
      * @return name
      */
    public String getName() {
        return name;
    }
​
    /**
      * set up
      * @param name
      */
    public void setName(String name) {
         = name;
    }
​
    /**
      * Get
      * @return age
      */
    public int getAge() {
        return age;
    }
​
    /**
      * set up
      * @param age
      */
    public void setAge(int age) {
         = age;
    }
​
    public String toString() {
        return "Student{name = " + name + ", age = " + age + "}";
    }
}
​
​
​
//Code in the test class://Requirement 1://Get empty parameters and create an object​
//1. Get the overall bytecode file objectClass clazz = (".");
//2. Construction method for obtaining empty parametersConstructor con = ();
//3. Create an object using the empty parameter construction methodStudent stu = (Student) ();
(stu);
​
​
("=============================================");
​
​
//Code in the test class://Requirement 2://Get the parameter structure and create an object//1. Get the overall bytecode file objectClass clazz = (".");
//2. Obtain the parameterized construction methodConstructor con = (, );
//3. Temporarily modify the access rights of the constructor (violent reflection)(true);
//4. Create an object directlyStudent stu = (Student) ("zhangsan", 23);
(stu);

public class ReflectDemo4 {
    public static void main(String[] args) throws ClassNotFoundException, NoSuchFieldException {
        //Get member variable object​
        //1. Get the class object        Class clazz = ("");
​
        //2. Obtaining the object (Field object) of member variables can only obtain public modified        Field[] fields1 = ();
        for (Field field : fields1) {
            (field);
        }
​
        ("===============================");
​
        //Get the object of member variable (public + private)        Field[] fields2 = ();
        for (Field field : fields2) {
            (field);
        }
​
        ("===============================");
        //Get a single member variable object        //If the obtained attribute does not exist, an exception will be reported        //Field field3 = ("aaa");
        //(field3);//NoSuchFieldException
​
        Field field4 = ("gender");
        (field4);
​
        ("===============================");
        //Get a single member variable (private)        Field field5 = ("name");
        (field5);
​
    }
}
​
​
​
public class Student {
    private String name;
​
    private int age;
​
    public String gender;
​
    public String address;
​
​
    public Student() {
    }
​
    public Student(String name, int age, String address) {
         = name;
         = age;
         = address;
    }
​
​
    public Student(String name, int age, String gender, String address) {
         = name;
         = age;
         = gender;
         = address;
    }
​
    /**
      * Get
      * @return name
      */
    public String getName() {
        return name;
    }
​
    /**
      * set up
      * @param name
      */
    public void setName(String name) {
         = name;
    }
​
    /**
      * Get
      * @return age
      */
    public int getAge() {
        return age;
    }
​
    /**
      * set up
      * @param age
      */
    public void setAge(int age) {
         = age;
    }
​
    /**
      * Get
      * @return gender
      */
    public String getGender() {
        return gender;
    }
​
    /**
      * set up
      * @param gender
      */
    public void setGender(String gender) {
         = gender;
    }
​
    /**
      * Get
      * @return address
      */
    public String getAddress() {
        return address;
    }
​
    /**
      * set up
      * @param address
      */
    public void setAddress(String address) {
         = address;
    }
​
    public String toString() {
        return "Student{name = " + name + ", age = " + age + ", gender = " + gender + ", address = " + address + "}";
    }
}

public class ReflectDemo5 {
    public static void main(String[] args) throws ClassNotFoundException, NoSuchFieldException, IllegalAccessException {
        Student s = new Student("zhangsan",23,"Guangzhou");
        Student ss = new Student("lisi",24,"Beijing");
​
        //need:        //Use reflection to get member variables and get values ​​and modify values​
        //1. Get the class object        Class clazz = ("");
​
        //2. Get name member variable        //field means the object with the attribute name        Field field = ("name");
        //Temporarily modify his access rights        (true);
​
        //3. Set (modify) the value of name        //Parameter 1: Indicates which object's name to be modified?        //Parameter 2: How much does it mean to be modified?        (s,"wangwu");
​
        //3. Get the value of name        // means that I want to get the value of the name of this object        String result = (String)(s);
​
        //4. Print the results        (result);
​
        (s);
        (ss);
​
    }
}
​
​
public class Student {
    private String name;
    private int age;
    public String gender;
    public String address;
​
​
    public Student() {
    }
​
    public Student(String name, int age, String address) {
         = name;
         = age;
         = address;
    }
​
​
    public Student(String name, int age, String gender, String address) {
         = name;
         = age;
         = gender;
         = address;
    }
​
    /**
      * Get
      * @return name
      */
    public String getName() {
        return name;
    }
​
    /**
      * set up
      * @param name
      */
    public void setName(String name) {
         = name;
    }
​
    /**
      * Get
      * @return age
      */
    public int getAge() {
        return age;
    }
​
    /**
      * set up
      * @param age
      */
    public void setAge(int age) {
         = age;
    }
​
    /**
      * Get
      * @return gender
      */
    public String getGender() {
        return gender;
    }
​
    /**
      * set up
      * @param gender
      */
    public void setGender(String gender) {
         = gender;
    }
​
    /**
      * Get
      * @return address
      */
    public String getAddress() {
        return address;
    }
​
    /**
      * set up
      * @param address
      */
    public void setAddress(String address) {
         = address;
    }
​
    public String toString() {
        return "Student{name = " + name + ", age = " + age + ", gender = " + gender + ", address = " + address + "}";
    }
}

public class ReflectDemo6 {
    public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException {
        //1. Get the class object        Class<?> clazz = ("");
​
​
        //2. Obtain method        //getMethods can get the method of public modification in the parent class        Method[] methods1 = ();
        for (Method method : methods1) {
            (method);
        }
​
        ("===========================");
        //Get all methods (including private)        //But you can only get the methods in your own class        Method[] methods2 = ();
        for (Method method : methods2) {
            (method);
        }
​
        ("===========================");
        //Get the specified method (empty parameter)        Method method3 = ("sleep");
        (method3);
​
        Method method4 = ("eat",);
        (method4);
​
        //Get the specified private method        Method method5 = ("playGame");
        (method5);
    }
}

package .a02reflectdemo1;
​
import ;
import ;
​
public class ReflectDemo6 {
    public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException, InvocationTargetException, IllegalAccessException {
        //1. Get the bytecode file object        Class clazz = (".");
        
        //2. Get an object        //This object needs to be used to call the method        Student s = new Student();
        
        //3. Get a specified method        //Parameter 1: method name        //Parameter 2: Parameter list, if not, you can not write        Method eatMethod = ("eat",);
        
        //run        //Parameter 1: represents the method calling object        //Parameter 2: The actual parameters required by the method during runtime        //Note: If the method has a return value, then you need to receive the result of invoke        //If the method does not return value, no reception is required        String result = (String) (s, "Chongqing Noodles");
        (result);
​
    }
}
​
​
​
public class Student {
    private String name;
    private int age;
    public String gender;
    public String address;
​
​
    public Student() {
​
    }
​
    public Student(String name) {
         = name;
    }
​
    private Student(String name, int age) {
         = name;
         = age;
    }
​
    /**
      * Get
      * @return name
      */
    public String getName() {
        return name;
    }
​
    /**
      * set up
      * @param name
      */
    public void setName(String name) {
         = name;
    }
​
    /**
      * Get
      * @return age
      */
    public int getAge() {
        return age;
    }
​
    /**
      * set up
      * @param age
      */
    public void setAge(int age) {
         = age;
    }
​
    public String toString() {
        return "Student{name = " + name + ", age = " + age + "}";
    }
​
    private void study(){
        ("Students are studying");
    }
​
    private void sleep(){
        ("Students are sleeping");
    }
​
    public String eat(String something){
        ("Students are eating" + something);
        return "The student has finished eating, very happy";
    }
}

package ;
​
import ;
import ;
import ;
​
public class ReflectDemo8 {
    public static void main(String[] args) throws NoSuchMethodException, InvocationTargetException, IllegalAccessException {
        //1. Create collection object        ArrayList<Integer> list = new ArrayList<>();
        (123);
//        ("aaa");
​
        //2. Use reflection to run the add method to add string        //Because the reflection uses class bytecode file​
        //Get class object        Class clazz = ();
​
        //Get add method object        Method method = ("add", );
​
        //Operation method        (list,"aaa");
​
        //Print the collection        (list);
    }
}

private final byte[] value;

String s = "abc";
String ss = "abc";
// private final byte[] value= {97,98,99};
// There is no method to provide getvalue and setvalue to the outside, and the address value of the value record cannot be modified.// If we use reflection to get the address value.// It can also be modified, the final modified value// The address value of a truly immutable value array can still be modified using reflection, which is more dangerous​
//1. Get the class objectClass clazz = ();
​
//2. Get the value member variable (private)Field field = ("value");
//But this operation is very dangerous//The higher version of JDK has blocked this operation, and the lower version is still OK//Temporary modification permission(true);
​
//3. Get the address value of the value recordbyte[] bytes = (byte[]) (s);
bytes[0] = 100;
​
(s);//dbc
(ss);//dbc

public class ReflectDemo9 {
    public static void main(String[] args) throws IOException, ClassNotFoundException, NoSuchMethodException, InvocationTargetException, InstantiationException, IllegalAccessException {
        //1. Read the configuration file information        Properties prop = new Properties();
        FileInputStream fis = new FileInputStream("day14-code\\");
        (fis);
        ();
        (prop);
​
        String classname = ("classname") + "";
        String methodname = ("methodname") + "";
​
        //2. Get the bytecode file object        Class clazz = (classname);
​
        //3. Create an object of this class first        Constructor con = ();
        (true);
        Object o = ();
        (o);
​
        //4. Obtain the method object        Method method = (methodname);
        (true);
​
        //5. Operation method        (o);
​
​
    }
}
​
Information in the configuration file：
classname=.
methodname=sleep

public class MyReflectDemo {
    public static void main(String[] args) throws IllegalAccessException, IOException {
    /*
         For any object, you can save all the field names and values ​​of the object to a file
     */
       Student s = new Student("Little A",23,'female',167.5,"sleep");
       Teacher t = new Teacher("Broadcast girl",10000);
       saveObject(s);
    }
​
    //Save all member variable names and values ​​in the object to the local file    public static void saveObject(Object obj) throws IllegalAccessException, IOException {
        //1. Obtain the object of the bytecode file        Class clazz = ();
        //2. Create IO stream        BufferedWriter bw = new BufferedWriter(new FileWriter("myreflect\\"));
        //3. Get all member variables        Field[] fields = ();
        for (Field field : fields) {
            (true);
            //Get the name of the member variable            String name = ();
            //Get the value of the member variable            Object value = (obj);
            //Write out the data            (name + "=" + value);
            ();
        }
​
        ();
​
    }
}
public class Student {
    private String name;
    private int age;
    private char gender;
    private double height;
    private String hobby;
​
    public Student() {
    }
​
    public Student(String name, int age, char gender, double height, String hobby) {
         = name;
         = age;
         = gender;
         = height;
         = hobby;
    }
​
    /**
      * Get
      * @return name
      */
    public String getName() {
        return name;
    }
​
    /**
      * set up
      * @param name
      */
    public void setName(String name) {
         = name;
    }
​
    /**
      * Get
      * @return age
      */
    public int getAge() {
        return age;
    }
​
    /**
      * set up
      * @param age
      */
    public void setAge(int age) {
         = age;
    }
​
    /**
      * Get
      * @return gender
      */
    public char getGender() {
        return gender;
    }
​
    /**
      * set up
      * @param gender
      */
    public void setGender(char gender) {
         = gender;
    }
​
    /**
      * Get
      * @return height
      */
    public double getHeight() {
        return height;
    }
​
    /**
      * set up
      * @param height
      */
    public void setHeight(double height) {
         = height;
    }
​
    /**
      * Get
      * @return hobby
      */
    public String getHobby() {
        return hobby;
    }
​
    /**
      * set up
      * @param hobby
      */
    public void setHobby(String hobby) {
         = hobby;
    }
​
    public String toString() {
        return "Student{name = " + name + ", age = " + age + ", gender = " + gender + ", height = " + height + ", hobby = " + hobby + "}";
    }
}
public class Teacher {
    private String name;
    private double salary;
​
    public Teacher() {
    }
​
    public Teacher(String name, double salary) {
         = name;
         = salary;
    }
​
    /**
      * Get
      * @return name
      */
    public String getName() {
        return name;
    }
​
    /**
      * set up
      * @param name
      */
    public void setName(String name) {
         = name;
    }
​
    /**
      * Get
      * @return sales
      */
    public double getSalary() {
        return salary;
    }
​
    /**
      * set up
      * @param sales
      */
    public void setSalary(double salary) {
         = salary;
    }
​
    public String toString() {
        return "Teacher{name = " + name + ", salary = " + salary + "}";
    }
}
​

public class Test {
    public static void main(String[] args) {
    /*
         need:
             People outside want big stars to sing a song
              1. Get the proxy object
                 Agent object = (the object of the big star);
              2. Call the agent's singing method again
                 Agent object. Singing method ("just because you are too beautiful");
      */
        //1. Get the proxy object        BigStar bigStar = new BigStar("Brother Chicken");
        Star proxy = (bigStar);
​
        //2. Call the singing method        String result = ("Just because you are too beautiful");
        (result);
    }
}
/*
 *
 * The function of the class:
 * Create a proxy
 *
 * */
public class ProxyUtil {
    /*
     *
     * Function of the method:
     * Create an agent for a star object
     *
     * Formal parameters:
     * The celebrity object being represented
     *
     * Return value:
     * Agent created for celebrities
     *
     *
     *
     * need:
     * People outside want big stars to sing a song
     * 1. Get the proxy object
     * Agent object = (the object of the big star);
     * 2. Call the agent's singing method again
     * Agent object. Singing method ("just because you are too beautiful");
     * */
    public static Star createProxy(BigStar bigStar){
       /* Class: Provides a method to generate proxy objects for objects:
 ​
         public static Object newProxyInstance(ClassLoader loader, Class<?>[] interfaces, InvocationHandler h)
         Parameter 1: Used to specify which class loader to load the generated proxy class
         Parameter 2: Specify interfaces, these interfaces are used to specify what the generated agent is, that is, what methods are there
         Parameter 3: Used to specify what the generated proxy object should do*/
        Star star = (Star) (
                (),// Parameter 1: Used to specify which class loader to use to load the generated proxy class                new Class[]{},//Parameter 2: Specify interfaces, these interfaces are used to specify what the generated agent will be, that is, what methods are there                // Parameter 3: Used to specify what the generated proxy object should do                new InvocationHandler() {
                    @Override
                    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                        /*
                         * Parameter 1: Agent object
                         * Parameter 2: Method to run sing
                         * Parameter 3: The actual parameters passed when calling the sing method
                         * */
                        if("sing".equals(())){
                            ("Prepare the microphone and collect the money");
                        }else if("dance".equals(())){
                            ("Prepare the venue and collect money");
                        }
                        //Go to find a big star to start singing or dancing                        //The code expression form: call the method of singing or dancing in the big stars                        return (bigStar,args);
                    }
                }
        );
        return star;
    }
}
public interface Star {
    //We can define all methods that want to be proxyed in the interface    //Sing    public abstract String sing(String name);
    //Dance    public abstract void dance();
}
public class BigStar implements Star {
    private String name;
​
​
    public BigStar() {
    }
​
    public BigStar(String name) {
         = name;
    }
​
    //Sing    @Override
    public String sing(String name){
        ( + "Singing" + name);
        return "Thanks";
    }
​
    //Dance    @Override
    public void dance(){
        ( + "Dancing");
    }
​
    /**
      * Get
      * @return name
      */
    public String getName() {
        return name;
    }
​
    /**
      * set up
      * @param name
      */
    public void setName(String name) {
         = name;
    }
​
    public String toString() {
        return "BigStar{name = " + name + "}";
    }
}
​

/*
 * The function of the class:
 * Create a proxy
 * */
public class ProxyUtil {
    public static Star createProxy(BigStar bigStar){
        public static Object newProxyInstance(ClassLoader loader, Class<?>[] interfaces, InvocationHandler h)
        Star star = (Star) (
                (),
                new Class[]{},
                new InvocationHandler() {
                    @Override
                    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                        if("cleanWC".equals(())){
                            ("Intercept, do not call the big star's method");
                            return null;
                        }
                        //If it is another method, it will be executed normally                        return (bigStar,args);
                    }
                }
        );
        return star;
    }
}

public class MyProxyDemo1 {
    public static void main(String[] args) {
        //Dynamic code can be enhanced or intercepted        //1. Create a real worker        ArrayList<String> list = new ArrayList<>();
​
        //2. Create a proxy object        //Parameter 1: Class loader.  Current class name.()        // Find who it is and load the current class into memory. I will ask him to do something for me to load the subsequent proxy class into memory.​
        //Parameter 2: It is an array, which writes the interface's bytecode file object in the array.        // If List is written, it means a proxy. You can proxy all methods in the List interface. These methods can be enhanced or intercepted        // However, you must write the interface that is truly implemented by ArrayList        // Assuming that in the second parameter, the MyInter interface is written, it is wrong.        // Because ArrayList does not implement this interface, it is impossible to enhance or intercept the methods in this interface        // Parameter 3: Anonymous internal class used to create proxy objects        List proxyList = (List) (
                //Parameter 1: Class loader                (),
                //Parameter 2: It is an array that represents the scope of methods that the proxy object can proxy                new Class[]{},
                //Parameter 3: The essence is the proxy object                new InvocationHandler() {
                    @Override
                    //The significance of invoke method parameters                    //Parameter 1: represents the proxy object, generally not needed (understand)                    // Parameter 2: It is the method name. We can judge the method name, whether it is enhanced or intercepted                    //Parameter 3: It is the parameter passed when calling the method in the third step below.                    //Example 1:                    //("A Wei is so handsome");                    //At this time parameter 2 is the method name of add                    //At this time, parameter three args[0] is Awei so handsome                    //Example 2:                    //(1, "aaa");
                    //At this time parameter two is the method name set                    //At this time, parameter three args[0] is 1 args[1]"aaa"                    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                        //Make an enhancement to the add method, the statistics take time                        if (().equals("add")) {
                            long start = ();
                            //Calling the collection method to truly add data                            (list, args);
                            long end = ();
                            ("Time-consuming:" + (end - start));
                            //Return is required, and the return value must be consistent with the actual enhancement or intercepting method.                            return true;
                        }else if(().equals("remove") && args[0] instanceof Integer){
                            ("Intercepted method of deletion by index");
                            return null;
                        }else if(().equals("remove")){
                            ("Intercepted method of deletion according to object");
                            return false;
                        }else{
                            //If the current call is another method, we neither enhance nor intercept                            (list,args);
                            return null;
                        }
                    }
                }
        );
​
        //3. Call method        //If the caller is a list, it is like bypassing the second step of the code and adding elements directly        //If the caller is a proxy object, this era agent can help us enhance or intercept​
        //Every time a method is called, the collection will not be operated directly        // Instead, call the invoke in the proxy first, make judgments in the invoke method, which can enhance or intercept        ("aaa");
        ("bbb");
        ("ccc");
        ("ddd");
​
        (0);
        ("aaa");
​
​
        //Print the collection        (list);
    }
}