Spring AOP

AOP stands for Aspect-Oriented Programming, which is programming for cross-sectional concerns. Cross-sectional concerns refer to functions common to multiple modules. For example, logging is a function that both the member module and the bulletin board module have. The following AOP example will show us how to separate cross-sectional concerns.

Add the following to pom.xml. 

<dependency>
  <groupId>org.springframework</groupId>
  <artifactId>spring-aspects</artifactId>
  <version>${spring.version}</version>
</dependency>
<!-- https://mvnrepository.com/artifact/org.aspectj/aspectjweaver -->
<dependency>
  <groupId>org.aspectj</groupId>
  <artifactId>aspectjweaver</artifactId>
  <version>1.9.19</version>
</dependency>

Create TestLogger.java like below.

TestLogger.java
package net.java_school.commons;

import org.aspectj.lang.JoinPoint;
import org.aspectj.lang.annotation.AfterReturning;
import org.aspectj.lang.annotation.Aspect;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

@Aspect
public class TestLogger {
  Logger logger = LoggerFactory.getLogger(this.getClass());
  
  @AfterReturning("execution(* net.java_school.bank.BankDao.deposit(..))")
  public void depositLog(JoinPoint point) {
    Object[] a = point.getArgs();
    String accountNo = (String) a[0];
    Long amount = (Long) a[1];
    String methodName = point.getSignature().getName();
    logger.debug("{}|{}|{}", methodName, accountNo, amount);
  }
  
  @AfterReturning("execution(* withdraw(..)) && args(accountNo, amount)")
  public void withdrawLog(String accountNo, double amount) {
    logger.debug("WITHDRAW|{}|{}", accountNo, amount);
  }
}

Remove logging code from all Java sources like below.

MyBankDao.java
package net.java_school.bank;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;

public class MyBankDao implements BankDao {
  static final String URL = "jdbc:oracle:thin:@127.0.0.1:1521:XE";
  static final String USER = "scott";
  static final String PASSWORD = "tiger";
  
  //..omit..
  
  @Override
  public void deposit(String accountNo, double amount) {
    Connection con = null;
    PreparedStatement pstmt = null;
    
    String sql = "UPDATE bankaccount " +
        "SET balance = balance + ? " +
        "WHERE accountNo = ?";
    
    try {
      con = getConnection();
      pstmt = con.prepareStatement(sql);
      pstmt.setLong(1, amount);
      pstmt.setString(2, accountNo);
      pstmt.executeUpdate();
    } catch (SQLException e) {
      e.printStackTrace();
    } finally {
      close(null, pstmt, con);
    }
  }

  @Override
  public void withdraw(String accountNo, double amount) {
    Connection con = null;
    PreparedStatement pstmt = null;
    
    String sql = "UPDATE bankaccount " +
        "SET balance = balance - ? " +
        "WHERE accountNo = ?";
    
    try {
      con = getConnection();
      pstmt = con.prepareStatement(sql);
      pstmt.setLong(1, amount);
      pstmt.setString(2, accountNo);
      pstmt.executeUpdate();
    } catch (SQLException e) {
      e.printStackTrace();
    } finally {
      close(null, pstmt, con);
    }
  }
  
  //..omit..
  
}

XML configuration

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

  <bean id="testLogger" class="net.java_school.commons.TestLogger" />
    
  <bean id="bankUi" class="net.java_school.bank.BankUi">
    <property name="stream" value="#{T(System).out}" />
    <property name="bank" ref="myBank" />
  </bean>

  <bean id="myBank" class="net.java_school.bank.MyBank">
    <property name="dao" ref="myBankDao" />
  </bean>

  <bean id="myBankDao" class="net.java_school.bank.MyBankDao">
  </bean>
    
</beans>

Modify the main method of BankUi.java. 

ClassPathXmlApplicationContext ctx = new ClassPathXmlApplicationContext("applicationContext.xml"); //XML
//AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext(BankConfig.class); //JavaConfig

JavaConfig configuration

BankConfig.java
package net.java_school.bank;

import net.java_school.commons.TestLogger;

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

@Configuration
@EnableAspectJAutoProxy
public class BankConfig {
  
  @Bean
  public TestLogger testLogger() {
    return new TestLogger();
  }

  @Bean
  public BankDao myBankDao() {
    return new MyBankDao();
  }

  @Bean
  public Bank myBank() {
    Bank bank = new MyBank();
    bank.setDao(myBankDao());
    return bank;
  }

  @Bean
  public BankUi bankUi() {
    BankUi ui = new BankUi();
    ui.setBank(myBank());
    ui.setStream(System.out);
    return ui;
  }
}

First, comment out all contents of the beans element in applicationContext.xml and modify the main method of BankUi.java as follows. 

//ClassPathXmlApplicationContext ctx = new ClassPathXmlApplicationContext("applicationContext.xml"); //XML
AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext(BankConfig.class); //JavaConfig

We confirmed that the limitations of Object-Oriented Programming could be supplemented by applying AOP to the cross-sectional concerns of the system in this section.

Final Source: https://github.com/kimjonghoon/aop

References