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Proxy mode

I recommend everyone to watch the video of the power node , which is more helpful for understanding

Proxy mode

1. How to understand the proxy model

Understand the agent mode through Lao Du's method (analogous to the real scene), as follows:

1. The three roles of proxy mode: target object, proxy object, public interface

	filming	Proxy mode
first role	actor	target
second role	stuntman	proxy object
third role	Actors and stand-ins have the same action behavior	Public interface of target object and proxy object

Here is the code to show:

The relationship diagram of the three is as follows:

The relationship between the three is that both the target object and the proxy object implement the same public interface

2. Three functions of the proxy mode

1) Protect yourself

In the program, when an object needs to be protected, you can consider using a proxy object to complete a certain behavior.
In real scenes, actors are afraid to let a stand-in actor (agent analysis) perform in order to protect themselves

2) Enhanced functions

In the program, when you need to enhance the function of an object , you can consider finding an agent to enhance it.
In real scenarios, for example, if we want to rent a house, we can rent it ourselves (target object), or we can find an intermediary group (proxy object), which realizes enhanced functions

3) Agent interaction

In the program, when the A object cannot directly interact with the B object, the proxy mode can also be used to solve it.
In the real scene, the man and woman did not meet before the blind date, and the matchmaker realized the communication between different objects by contacting the parents (proxy objects) of both parties.

3. Implementation of the proxy mode

Divided into static proxy and dynamic proxy

will be elaborated next

2. Static proxy

1. Explain in simple terms, starting from a common scenario in real business

Introduce the example of Lao Du:

A certain business module of a certain project has been running normally for many years, and the project manager requires these modules to be optimized. The first step is a simple requirement: to display the execution time of each module (method). For example, I have such a demand now, how should I realize it?

1) Method 1, hard coding, directly modify the original business code, and add a timing business code based on it.

Analyze its advantages and disadvantages

Advantages: simple and easy to understand, hard coding is very rough
Disadvantages: Violates the OCP opening and closing principle , and the code is redundant

Insert a knowledge point, what is the OCP opening and closing principle?

The Open/Closed Principle (OCP) stipulates that "objects (classes, modules, functions, etc.) in software should be open for extension, but closed for modification. " Its meaning is that a software entity should implement changes through expansion, rather than through modification of existing codes.

This feature is especially valuable in a production environment, where changes to source code require code reviews, unit tests, and the like to ensure quality for use in production.

2) Method 2: Create a new class to inherit the original business, and rewrite the method of the parent class in the subclass to achieve business requirements

Analysis of advantages and disadvantages

Advantages: Comply with the OCP opening and closing principle
Disadvantages: the code is as redundant, and the degree of coupling is increased (because of the inheritance relationship)

3) Introduce proxy mode, that is, use proxy objects to achieve function enhancement

As mentioned just now, the three roles required by the proxy mode: target object, proxy object, and public interface. [Target object + announcement interface] has been realized in normal business, and what is still missing is a proxy object.

Then the proxy object is very simple in the coding layer. Create an object and implement the announced interface. At the same time, when the client is required to use the proxy object, it is the same as using the target object !

So, how is the static proxy implemented in the code?

First create a proxy object and implement the same public interface
Rewrite the parent class method normally, and write the business logic required to enhance the function
reference target object (how to reference?
In the proxy object, call the corresponding method of the target object,

How to reference the target object? look at the code

Insert knowledge points: the relationship between classes and the second [generalization relationship and association relationship]

The generalization relationship is inheritance, which is a relationship is aof

For example, an apple is a fruit and a cat is an animal. This is a generalization relationship.

An association relationship, that is, a reference, is a has arelationship of

For example, a person owns an apple, and a person owns a cat. This is an association relationship.

2. What are the advantages and disadvantages of the static proxy mode

Advantages :

Solved the OCP problem
The association relationship is used, the has a relationship is introduced, and the coupling is reduced

shortcoming

The code is still redundant. If there are too many interfaces in the system, and each interface has a proxy object, [ class explosion ] will occur
Not easy to maintain (too many classes are not conducive to modifying the business later

In order to overcome the shortcomings of the static proxy mode, a dynamic proxy is introduced

The technology of dynamically generating bytecode proxy classes in memory is called dynamic proxy. Dynamic proxy
is still proxy mode, but with the addition of bytecode generation technology , it can dynamically generate a cLass bytecode for us in memory. This word Section code is the proxy class.

3. Dynamic agent

1. What is a dynamic proxy?

As mentioned earlier, dynamic proxy is the technology of dynamically generating [bytecode proxy class] in [memory]. (Although there is no need for developers to write, the proxy object still exists at the memory level]