Spring 3 part 6: Spring AOP

This is the 6th part of the Spring 3 Series.

AOP Concepts

  • Joinpoint: Joinpoint is the point in an application at which additional logic can be inserted. For example method invocation that is the only Spring support joinpoint type.
  • Advice: Advice is executed at a particular joinpoint in an application. NOTE: no advices for final classes. All the advisors need to implement the Advisor interface. There are two kind of advisors available in the Spring: IntrodcutionAdvisor and PointcutAdvisor. Spring defines 6 difference advices: before(MethodBeforeAdvice),  after returning (AfterReturningAdvice), after(AfterAdvice), around (MethodInterceptor), Throws (ThrowsAdvice), and Introduction (IntroductionInterceptor).
  • Pointcuts: A pointcut is a collection of joinpoints that define when advice should be executed. For example, collection of all method invocations in a particular class.
  • Aspect: An aspect is the combination of advice and pointcuts. This combination immerge the logic which we used to execute in the application.
  • Weaving: In compile-time or runtime, process of actually inserting aspects into the application code is called weaving.
  • Target: Target is an object whose execution follow is modified by AOP process.
  • Introduction: Introducing new methods or field to modify the structure of the existing object.

Advices

aop-class-diagram

There are 6 advices as shown in the above diagram. you can create advices for the above implementations.

Here some basic thing you should know

  • To enable @AspectJ support with XML based configuration use the <aop:aspectj-autoproxy>
  • Declare an aspect either in the config xml as regular bean or @Aspect in the bean (@Aspect is not sufficient to detect the aspect from the classpath, therefore need to use @Component).
  • Spring only support method execution joint points. Pointcut include two parts, pointcut expression and the method signature.  Use either @Pointcut or <aop:config> and <aop:advicesor>. It is best practice to build more complex pointcut expressions out of smaller named components.
  • Declare an advice kind of advice shown in the above figure.

According to the spring reference, @AspectJ is recommended to use in regular applications.

Example

Let’s see the example. This is very simple example: the Hello service with one single method that is sayHello(). This example includes the unit testing.

Here the service interface

package au.com.ojitha.blogspot.example.part6;

public interface Hello<T> {

    public boolean sayHello(T name);

}

Then the Service

package au.com.ojitha.blogspot.example.part6;

import org.springframework.stereotype.Component;

@Component
public class HelloService implements Hello<Message> {

    /* (non-Javadoc)
     * @see au.com.ojitha.blogspot.example.part6.Hello#sayHello(java.lang.String)
     */

    public boolean sayHello(Message name){
        //System.out.println(name+", Hello");
        return true;
    }
}

The sayHello(..) method pass the Message as a parameter

package au.com.ojitha.blogspot.example.part6;

public class Message {
    private String message;

    public String getMessage() {
        return message;
    }

    public void setMessage(String message) {
        this.message = message;
    }
}

Here the aspect with advices

package au.com.ojitha.blogspot.example.part6;

import org.apache.log4j.Logger;
import org.aspectj.lang.ProceedingJoinPoint;
import org.aspectj.lang.annotation.After;
import org.aspectj.lang.annotation.AfterReturning;
import org.aspectj.lang.annotation.Around;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Before;
import org.aspectj.lang.annotation.Pointcut;
import org.springframework.stereotype.Component;

@Aspect
@Component
public class LoggerAspect {
    
    Logger log = Logger.getLogger(LoggerAspect.class);

    @Pointcut("execution(* au.com.ojitha.blogspot.example.part6.Hello+.sayHello(..)) &&"+"args(message,..)")
    public void methodToBeLogged(Message message){}
    
    @Before("methodToBeLogged(message)")
    public void displayBefore(Message message){
        log.info("Before Advice by "+message.getMessage());
    }
    
    @After("methodToBeLogged(message)")
    public void displayAfter(Message message){
        log.info("After Advice by "+message.getMessage());
    }
    
    @AfterReturning(pointcut="methodToBeLogged(message)", returning="retval")
    public void displayAfterReturning(Message message, Object retval){
        log.info("After Returning Advice by "+message.getMessage()+" and returned the value: "+retval);
        
    }
    
    @Around("methodToBeLogged(message)")
    public boolean displayAround(ProceedingJoinPoint pjp, Message message) throws Throwable{
        log.info("= Around Advice = before the method execute...");
        boolean retval = (boolean)pjp.proceed();
        log.info("= Around Advice = after the method executed...");
        return retval;
    }
}

In the above pointcut, “…Hello+.sayHello…”  shows the use of Java Generic interface.

Here the configuration file:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:context="http://www.springframework.org/schema/context"
    xmlns:aop="http://www.springframework.org/schema/aop"
    xsi:schemaLocation="http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-3.2.xsd
        http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.2.xsd
        http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.2.xsd">

    <description>Example configuration to get you started.</description>

    <aop:aspectj-autoproxy/>
    <context:component-scan base-package="au.com.ojitha.blogspot.example.part6" />

</beans>

As shown in the above listing, aspectj-autoproxy is the key player. In this example I am using JDK proxies only as shown in the following maven pom.xml file.

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
    <modelVersion>4.0.0</modelVersion>
    <groupId>org.springframework.samples.spring</groupId>
    <artifactId>spring-utility</artifactId>
    <version>1.0.0.CI-SNAPSHOT</version>
    <packaging>jar</packaging>
    <name>Spring Utility</name>
    <url>http://www.springframework.org</url>
    <description>
        <![CDATA[
      This project is a minimal jar utility with Spring configuration.
    ]]>
    </description>
    <properties>
        <maven.test.failure.ignore>false</maven.test.failure.ignore>
        <spring.framework.version>3.2.2.RELEASE</spring.framework.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.7</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-test</artifactId>
            <version>${spring.framework.version}</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-context</artifactId>
            <version>${spring.framework.version}</version>
        </dependency>
        <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>1.2.14</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-aop</artifactId>
            <version>${spring.framework.version}</version>
        </dependency>
        <dependency>
            <groupId>org.aspectj</groupId>
            <artifactId>aspectjrt</artifactId>
            <version>1.7.2</version>
        </dependency>
        <dependency>
            <groupId>org.aspectj</groupId>
            <artifactId>aspectjweaver</artifactId>
            <version>1.7.2</version>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <configuration>
                    <source>1.7</source>
                    <target>1.7</target>
                </configuration>
            </plugin>

        </plugins>
    </build>
</project>

Here the simple test case to run

package au.com.ojitha.blogspot.example.part6;

import static org.junit.Assert.assertNotNull;

import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;

@ContextConfiguration
@RunWith(SpringJUnit4ClassRunner.class)
public class HelloServiceConfigurationTests {
    
    Message message;

    @Autowired
    private Hello helloWorld;

    @Before
    public void setup(){
        message = new Message();
        message.setMessage("Ojitha");
    }
    
    @Test
    public void testSimpleProperties() throws Exception {
        assertNotNull(helloWorld);
        
    }
    
    @Test
    public void testSayHello(){
        assertNotNull(helloWorld.sayHello(this.message));
    }
    
}

 

Here the output,

22:02:53,811  INFO st.context.support.AbstractContextLoader: 216 - Detected default resource location "classpath:/au/com/ojitha/blogspot/example/part6/HelloServiceConfigurationTests-context.xml" for test class [au.com.ojitha.blogspot.example.part6.HelloServiceConfigurationTests].
22:02:53,815  INFO ort.AbstractDelegatingSmartContextLoader: 168 - GenericXmlContextLoader detected default locations for context configuration [ContextConfigurationAttributes@a377714 declaringClass = 'au.com.ojitha.blogspot.example.part6.HelloServiceConfigurationTests', locations = '{classpath:/au/com/ojitha/blogspot/example/part6/HelloServiceConfigurationTests-context.xml}', classes = '{}', inheritLocations = true, initializers = '{}', inheritInitializers = true, name = [null], contextLoaderClass = 'org.springframework.test.context.ContextLoader'].
22:02:53,817  INFO pport.AnnotationConfigContextLoaderUtils: 111 - Could not detect default configuration classes for test class [au.com.ojitha.blogspot.example.part6.HelloServiceConfigurationTests]: HelloServiceConfigurationTests does not declare any static, non-private, non-final, inner classes annotated with @Configuration.
22:02:54,002  INFO eans.factory.xml.XmlBeanDefinitionReader: 315 - Loading XML bean definitions from class path resource [au/com/ojitha/blogspot/example/part6/HelloServiceConfigurationTests-context.xml]
22:02:54,165  INFO eans.factory.xml.XmlBeanDefinitionReader: 315 - Loading XML bean definitions from class path resource [META-INF/spring/app-context.xml]
22:02:54,376  INFO ontext.support.GenericApplicationContext: 510 - Refreshing org.springframework.context.support.GenericApplicationContext@801b120: startup date [Fri Mar 29 22:02:54 EST 2013]; root of context hierarchy
22:02:54,554  INFO ctory.support.DefaultListableBeanFactory: 596 - Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@28826c2c: defining beans [org.springframework.aop.config.internalAutoProxyCreator,exampleService,helloService,loggerAspect,org.springframework.context.annotation.internalConfigurationAnnotationProcessor,org.springframework.context.annotation.internalAutowiredAnnotationProcessor,org.springframework.context.annotation.internalRequiredAnnotationProcessor,org.springframework.context.annotation.internalCommonAnnotationProcessor,org.springframework.context.annotation.ConfigurationClassPostProcessor.importAwareProcessor]; root of factory hierarchy
22:02:55,011  INFO itha.blogspot.example.part6.LoggerAspect:  40 - = Around Advice = before the method execute...
22:02:55,014  INFO itha.blogspot.example.part6.LoggerAspect:  24 - Before Advice by Ojitha
22:02:55,016  INFO itha.blogspot.example.part6.LoggerAspect:  42 - = Around Advice = after the method executed...
22:02:55,017  INFO itha.blogspot.example.part6.LoggerAspect:  29 - After Advice by Ojitha
22:02:55,018  INFO itha.blogspot.example.part6.LoggerAspect:  34 - After Returning Advice by Ojitha and returned the value: true
22:02:55,024  INFO ontext.support.GenericApplicationContext:1042 - Closing org.springframework.context.support.GenericApplicationContext@801b120: startup date [Fri Mar 29 22:02:54 EST 2013]; root of context hierarchy
22:02:55,026  INFO ctory.support.DefaultListableBeanFactory: 444 - Destroying singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@28826c2c: defining beans [org.springframework.aop.config.internalAutoProxyCreator,exampleService,helloService,loggerAspect,org.springframework.context.annotation.internalConfigurationAnnotationProcessor,org.springframework.context.annotation.internalAutowiredAnnotationProcessor,org.springframework.context.annotation.internalRequiredAnnotationProcessor,org.springframework.context.annotation.internalCommonAnnotationProcessor,org.springframework.context.annotation.ConfigurationClassPostProcessor.importAwareProcessor]; root of factory hierarchy

In the above output line 8 to 12 shows the behaviour of the advices.

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You can download the source code from the GitHub.

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