The @Before advice in Spring AOP

In this tutorial, you will learn about the @Before advice in Spring AOP. Before proceeding with this tutorial, make sure you have a good understanding of the AOP terminologies. You already know about the 5 types of advice from the previous article as listed below.

Before advice – @Before
Around advice – @Around
After returning – @AfterReturning
After throwing – @AfterThrowing
After (finally) advice – @After

Execution of @Before Advice

A @Before advice is executed before the method execution. In technical terms, an advice annotated with @Before is executed before the matched Join points methods get executed. Before advice can be applied to one or more matching Join points.

import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Before;

@Aspect
public class BeforeExample {

    @Before("execution(* com.jbd.myapp.service.*.*(..)")
    public void doAccessCheck() {
        // ...
    }

}

Steps to use @Before Advice annotation

Step-1: Add dependencies

Add the necessary dependencies to your pom.xml. Technically you only need the aspectjweaver and spring-aop jars. As this is a spring application, so we will also need the spring-core and spring-context jars. Additionally, you can add the JUnit and spring-test jars to run the test cases.

<dependencies>
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-core</artifactId>
      <version>5.2.2.RELEASE</version>
    </dependency>

    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-context</artifactId>
      <version>5.2.2.RELEASE</version>
    </dependency>

    <!-- Step-1 Add the dependencies -->
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-aop</artifactId>
      <version>5.2.2.RELEASE</version>
    </dependency>

    <dependency>
      <groupId>org.aspectj</groupId>
      <artifactId>aspectjweaver</artifactId>
     <version>1.9.5</version>
    </dependency>
<dependencies>

Step-2: Crete the Sample classes

Create the sample classes in their respective packages so that we have the example codes to apply before-advice. Basically we will create 2 repository classes, each with add() and delete() methods.

package c.jbd.saop.gettingstarted.dao;

import org.springframework.stereotype.Repository;

@Repository
public class ActorRepository {
  //Add an actor
  public ActorRepository add(String actorName) {
    if (actorName == null) {
      throw new RuntimeException("actorName is null", new NullPointerException());
    }
    System.out.println("New Actor added: " + actorName);
    return this;
  }

  //Delete an actor
  public boolean delete(String actorName) {
    if (actorName == null) {
      throw new RuntimeException("actorName is null", new NullPointerException());
    }
    System.out.println("Actor deleted: " + actorName);
    return true;
  }
}

package c.jbd.saop.gettingstarted.dao;

import org.springframework.stereotype.Repository;

@Repository
public class MovieRepository {
  //Add a movie method
  public MovieRepository add(String movieName) {
    if (movieName == null) {
      throw new RuntimeException("movieName is null", new NullPointerException());
    }
    System.out.println("New movie added: " + movieName);
    return this;
  }

  //Delete a movie
  public boolean delete(String movieName) {
    if (movieName == null) {
      throw new RuntimeException("movieName is null", new NullPointerException());
    }
    System.out.println("Movie deleted: " + movieName);
    return true;
  }
}

package c.jbd.saop.gettingstarted.config;

import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.EnableAspectJAutoProxy;

@Configuration
@ComponentScan("c.jbd.saop.gettingstarted")
public class ApplicationConfig {
}

Step-3: Enable AspectJ

Enable the AspectJ auto proxy by adding @EnableAspectJAutoProxy to the ApplicationConfig class as below. Basically, this will enable Spring-AOP in the application.

ackage c.jbd.saop.gettingstarted.config;

import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.EnableAspectJAutoProxy;

@Configuration
//Step-3 - Add the annotation
@EnableAspectJAutoProxy
@ComponentScan("c.jbd.saop.gettingstarted")
public class ApplicationConfig {
}

Step-4: Declare advice class

Now let’s create a class named BeforeAdvice as below. It is important to annotate the aspect class with @Aspect annotation to mark this as an aspect. We also need this to be picked by Spring, so use the @Configurartion annotation. We will revisit the expression inside the @Before annotation, which is also known as Pointcut.

package c.jbd.saop.gettingstarted.aspect;

import org.aspectj.lang.JoinPoint;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Before;
import org.springframework.context.annotation.Configuration;

@Configuration
@Aspect //Important to say this is an Aspect config class
public class BeforeAdvice {

  //execution(RETURN_TYPE PACKAGE.CLASS.METHOD(..PARAMETER_LIST))
  //execution(* PACKAGE.*.*(..))
  @Before("execution(* c.jbd.saop.gettingstarted.dao.*.add(..))")
  public void allDaoAddMethods(JoinPoint joinPoint) {
    System.out.println("Intercepted method: " + joinPoint);
    System.out.println("Arguments: " + joinPoint.getArgs());
    System.out.println(joinPoint.getTarget());
  }

  @Before("execution(* c.jbd.saop.gettingstarted.dao.*.*(..))")
  public void allDaoAnyMethod(JoinPoint joinPoint) {
    System.out.println("Intercepted method: " + joinPoint);
    System.out.println("Arguments: " + joinPoint.getArgs());
    System.out.println(joinPoint.getTarget());
  }
}

We created two Before aspects, each with separate Pointcut expression.
The first one is applied to add() methods of all the repository classes, and the second aspect is applied to all the methods of repository classes.
In other words, the second aspect will be called for add() as well as the delete() methods of ActorRepository and MovieRepository.

Instead of the @Configuration annotation, we can also make use of @Component for aspect classes. However, as we ourselves don’t need an instance of this, spring recommends using the @Configuration.

Step-5: Test the example
Finally, we will test the example to see its output. Will use the normal spring-test with junit-jupiter-api. So make sure you have the test dependencies as shown below.

.  <dependencies>
  ... 
   <!-- Test Dependencies-->
    <dependency>
      <groupId>org.junit.jupiter</groupId>
      <artifactId>junit-jupiter-api</artifactId>
      <version>5.5.2</version>
      <scope>test</scope>
    </dependency>

    <dependency>
      <groupId>org.junit.jupiter</groupId>
      <artifactId>junit-jupiter-engine</artifactId>
      <version>5.5.2</version>
      <scope>test</scope>
    </dependency>

    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-test</artifactId>
      <version>5.2.2.RELEASE</version>
      <scope>test</scope>
    </dependency>
  </dependencies>


...
<!-- Important for Jupiter-engine -->
<build>
    <plugins>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-surefire-plugin</artifactId>
        <version>3.0.0-M3</version>
      </plugin>
    </plugins>
  </build>
</project>

package c.jbd.saop.gettingstarted;

import c.jbd.saop.gettingstarted.config.ApplicationConfig;
import c.jbd.saop.gettingstarted.dao.ActorRepository;
import c.jbd.saop.gettingstarted.dao.MovieRepository;
import org.junit.jupiter.api.Assertions;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.test.context.junit.jupiter.SpringJUnitConfig;

@SpringJUnitConfig(ApplicationConfig.class)
public class TestBeforeAdvice {

  @Autowired
  private ActorRepository actorRepository;

  @Autowired
  private MovieRepository movieRepository;

  @Test
  public void testAddAspects() {
    actorRepository.add("Hrithik Roshan");
    movieRepository.add("Sholey");
  }
}

Output:

Intercepted method: execution(ActorRepository c.jbd.saop.gettingstarted.dao.ActorRepository.add(String))
Arguments: Hrithik Roshan
c.jbd.saop.gettingstarted.dao.ActorRepository@6e521c1e
Intercepted method: execution(ActorRepository c.jbd.saop.gettingstarted.dao.ActorRepository.add(String))
Arguments: Hrithik Roshan
c.jbd.saop.gettingstarted.dao.ActorRepository@6e521c1e
New Actor added: Hrithik Roshan

Intercepted method: execution(MovieRepository c.jbd.saop.gettingstarted.dao.MovieRepository.add(String))
Arguments: Sholey
c.jbd.saop.gettingstarted.dao.MovieRepository@61078690
Intercepted method: execution(MovieRepository c.jbd.saop.gettingstarted.dao.MovieRepository.add(String))
Arguments: Sholey
c.jbd.saop.gettingstarted.dao.MovieRepository@61078690
New movie added: Sholey

You can see in the above output, for add() methods of both Repository BeforeAdvice:allDaoAddMethods() and BeforeAdvice:allDaoAnyMethod() gets executed before the actual method calls.

Step-6: Additional tests
Now let’s just add another @Testcase to the TestBeforeAdvice class and observe the output.

@SpringJUnitConfig(ApplicationConfig.class)
public class TestBeforeAdvice {  
...
...
  @Test
  public void testDeleteAspects() {
    actorRepository.delete("John Doe");
    movieRepository.delete("Abc");
  }
}

Intercepted method: execution(boolean c.jbd.saop.gettingstarted.dao.ActorRepository.delete(String))
Arguments: John Doe
c.jbd.saop.gettingstarted.dao.ActorRepository@6e521c1e
Actor deleted: John Doe
Intercepted method: execution(boolean c.jbd.saop.gettingstarted.dao.MovieRepository.delete(String))
Arguments: Abc
c.jbd.saop.gettingstarted.dao.MovieRepository@61078690
Movie deleted: Abc

For both the delete() calls, only the BeforeAdvice:allDaoAnyMethod() gets executed as this is the only aspect that matches.

Conclusion:

I have tried to present a simple example to understand the working of @Before advice in spring AOP. Next, we will explore the Pointcut expression and @Pointcut annotation to reuse the expressions. Download the complete code example from GitHub.

Code example

Execution of @Before Advice

Steps to use @Before Advice annotation

Conclusion:

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