As the software development industry grows, software quality becomes an increasingly important issue. While ensuring software quality, developers also need to develop software with complete functions quickly and efficiently. Unit testing, reflection, annotation and dynamic proxy are just four important tools that help improve software quality and development efficiency.

This blog will explain in detail the concepts, usage scenarios and related technical points of these four tools in Java.

unit test

Unit testing is a very important part of software development. It is a testing method designed to check that the smallest unit of code - a function or method, behaves as expected. Through unit testing, problems in the code can be found as early as possible to ensure software quality.

In Java, commonly used unit testing frameworks include JUnit, TestNG, etc. They provide some commonly used assertion methods, such as assertEquals(), assertTrue(), etc., which can be used to check the correctness of the code.

Unit testing can quickly verify whether the code still works normally after the code is modified, which reduces the workload of manual testing and facilitates code maintenance and refactoring.

JUnit framework

JUnit is one of the most popular unit testing frameworks in Java. It provides some common assertion methods, such as assertEquals(), assertTrue(), etc. In addition, JUnit also provides some annotations to control the execution order and timeout period of test cases.

A test case in JUnit consists of one or more methods annotated with @Test. When executing a test case, JUnit will automatically execute the method annotated with @Test, and judge whether the test case passes according to the assertion result. In addition to the @Test annotation, JUnit also provides some other annotations, such as @Before, @After, @BeforeClass, @AfterClass, etc., which can perform some specific operations before and after test case execution.

Here is an example of a simple JUnit test case:

import org.junit.Test;
import static org.junit.Assert.assertEquals;

public class MyTest {
    
    @Test
    public void testAddition() {
        int result = Calculator.add(1, 2);
        assertEquals(3, result);
    }
    
}

TestNG framework

TestNG is another popular Java unit testing framework. Compared with JUnit, TestNG provides richer annotations and configuration options, enabling more complex test scenarios. For example, TestNG can support grouping of test cases, parallel execution, data-driven, etc.

A TestNG test case consists of one or more methods annotated with @Test. Unlike JUnit, TestNG also provides other annotations to control how test cases are executed. Such as @BeforeMethod, @AfterMethod, @BeforeClass, @AfterClass, etc., can perform some specific operations before and after test case execution.

Here is an example of a simple TestNG test case:

import org.testng.annotations.Test;
import static org.testng.Assert.assertEquals;

public class MyTest {
    
    @Test
    public void testAddition() {
        int result = Calculator.add(1, 2);
        assertEquals(3, result);
    }
    
}

reflection

Reflection in Java refers to dynamically obtaining class information and calling methods and properties of a class when the program is running. Through reflection, all methods and properties of a class can be inspected at runtime and invoked dynamically. This capability makes Java more flexible and extensible.

Java reflection mainly involves three classes: Class, Method and Field. The Class class represents a Java class, the Method class represents the methods in the class, and the Field class represents the attributes in the class.

Reflection usage scenarios include but are not limited to:

• Create objects dynamically
• Get class information dynamically
• Call methods and properties dynamically

Write generic code that can be applied to different classes and objects
The following is a simple Java reflection example that demonstrates how to dynamically obtain class information:

import java.lang.reflect.Field;
import java.lang.reflect.Method;

public class ReflectDemo {
    
    public static void main(String[] args) throws Exception {
        Class clazz = Class.forName("java.util.ArrayList");
        System.out.println("class name:" + clazz.getName());
        System.out.println("Attributes:");
        Field[] fields = clazz.getDeclaredFields();
        for (Field field : fields) {
            System.out.println(field.getName());
        }
        System.out.println("method:");
        Method[] methods = clazz.getDeclaredMethods();
        for (Method method : methods) {
            System.out.println(method.getName());
        }
    }
    
}

annotation

Java annotations are a way to add metadata to your code. Annotations themselves do not affect the running of the program, but can be used by programs such as compilers, tools, and frameworks to improve the readability and maintainability of the program.

Java annotations are divided into three categories: meta-annotations, custom annotations, and built-in annotations.

Meta-annotations are annotations used to annotate other annotations, including four annotations:

• @Target
• @Retention
• @Inherited
• @Documented

in:

• @Target is used to specify which elements the annotation can be used on
• @Retention is used to specify the life cycle of annotations
• @Inherited is used to specify whether the annotation can be inherited
• @Documented is used to specify whether the annotation is included in JavaDoc

Custom annotations are annotations defined by developers according to their own needs. The definition format of custom annotation is:
@interface annotation name { annotation member }
Among them, annotation members can be:

• basic type
• String type
• Class type
• enumerated type
• Annotation type
• its array type

Annotations built into Java include:

@Override: Used to indicate that the method is an override method in the parent class or interface.
@Deprecated: Used to indicate that the method is outdated and is not recommended for use.
@SuppressWarnings: Used to suppress warning messages generated by the compiler.

Below is a simple Java annotation example that demonstrates how to define and use custom annotations:

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface MyAnnotation {
    String value();
}

public class MyTest {
    
    @MyAnnotation("Test Methods")
    public void test() {
        System.out.println("Execute the test method");
    }
    
}

In the above code, we define a custom annotation @MyAnnotation, which can be used to annotate methods. There is a value member in the annotation, which is used to represent the description information of the method. In the MyTest class, we apply the @MyAnnotation annotation to the test method and specify the description information of the method. At actual runtime, we can use reflection to obtain annotation information and perform corresponding operations based on the annotation information.

dynamic proxy

Java dynamic proxy is a mechanism based on reflection, which can dynamically generate proxy classes and proxy objects at runtime, without the need to determine the types of proxy classes and proxy objects at compile time. Through dynamic proxy, we can add additional functions to the target object, such as logging, performance statistics, transaction processing, etc., without modifying the source code.

Java dynamic proxy mainly involves two classes: InvocationHandler and Proxy. The InvocationHandler interface contains an invoke method for executing methods on the proxy object. The Proxy class provides a newProxyInstance method for creating proxy objects.

Here is a simple Java dynamic proxy example that demonstrates how to add logging before and after method execution:

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;

// Define the Calculator interface, including the add method
public interface Calculator {
    int add(int a, int b);
}

// Implement the Calculator interface and implement the add method
public class CalculatorImpl implements Calculator {
    public int add(int a, int b) {
        return a + b;
    }
}

// Define the proxy class of Calculator and implement the InvocationHandler interface
public class CalculatorProxy implements InvocationHandler {
    private Object target;  // target object to proxy

    // Constructor, pass in the target object
    public CalculatorProxy(Object target) {
        this.target = target;
    }

    // Implement the invoke method of the InvocationHandler interface to enhance the method of the target object
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        System.out.println("Begin execution" + method.getName() + "method");  // Enhanced code: output the method name before the target method is executed
        Object result = method.invoke(target, args);  // Call the method of the target object
        System.out.println("end execution" + method.getName() + "method");  // Enhanced code: output the method name after the target method is executed
        return result;  // Returns the execution result of the target method
    }
}

public class Main {
    public static void main(String[] args) {
        Calculator calculator = new CalculatorImpl();  // create target object
        Calculator proxy = (Calculator) Proxy.newProxyInstance(
                calculator.getClass().getClassLoader(),  // Pass in the class loader of the target object
                calculator.getClass().getInterfaces(),  // The interface implemented by the incoming target object
                new CalculatorProxy(calculator)  // Pass in a custom InvocationHandler instance
        );
        System.out.println(proxy.add(1, 2));  // Call the method of the proxy object
    }
}

In the above code, we define a Calculator interface and a CalculatorImpl implementation class. Then, we created a Calculator proxy object using a dynamic proxy. When the proxy object calls the add method, it will automatically execute the invoke method in the CalculatorProxy class, and add log records before and after method execution. The final output is:

Begin execution add method
3
 end execution add method