Some project background: I am working with an application that runs on Java. My goal is to collect real-time data to send it to an API running on a local server. The application is packaged into a .jar file and I have no access to source code. (Aside from the question, I have attempted to decompile the class to add additional functionality; however, that did not end well, $access000...)

Having just learned about AOP, I ran to test my options. I spend over a week figuring out Maven Setup and AspectJ with it.

I set up a "helloworld" project in which I have been able to successfully weave aspects (from a .java file) into another .java file. My next step is to create an executable .jar file with the main class and weave the aspect .java class into it - then I would have achieved my desired outcome.

Is it possible to take a precompiled .jar file, put it into the project and write aspects for it?

I am not sure if I am misunderstanding something, I believe that should be something feasable.

From AspectJ Development Environment Guide:

In AspectJ tools, the aspectpath is where to find binary aspects. Like the classpath, it can include archives ( .jar and .zip files) and directories containing .class files in a package layout (since binary aspects are in .class files).

Some Reference information:

I am using Eclipse (4.23.0).
The project is a Maven project that I have added AspectJ support to (through conversion to an AspectJ project).
I have gone over a bunch of websites and StackOverflow responses figuring out AspectJ for Eclipse and found This Question. TL;DR: I used this site as AspectJ (Temporary Fix) Source for Eclipse: https://aspectj.dev/eclipse/ajdt/421

Project Structure

├── pom.xml
└── src
    ├── main
    │   └── java
    │       └── com
    │           └── hellomaven
    │               └── quickstart
    │                   ├── App.java
    │                   └── AppAspect.java
    └── test
        ├── java
        └── resources

POM.xml

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.hellomaven</groupId>
  <artifactId>quickstart</artifactId>
  <version>0.0.1-SNAPSHOT</version>
  <packaging>jar</packaging>
  <name>helloMaven</name>
  <description>test</description>

  <properties>
    <java.version>1.8</java.version>
    <junit.version>4.5</junit.version>

    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
  </properties>

  <build>
    <pluginManagement>
      <plugins>

        <plugin>
          <groupId>org.codehaus.mojo</groupId>
          <artifactId>aspectj-maven-plugin</artifactId>
          <version>1.9</version>
          <configuration>
            <showWeaveInfo>true</showWeaveInfo>
            <source>${java.version}</source>
            <target>${java.version}</target>
            <Xlint>ignore</Xlint>
            <complianceLevel>${java.version}</complianceLevel>
            <encoding>UTF-8</encoding>
            <verbose>true</verbose>
            <weaveDependencies>
              <weaveDependency>
                <groupId>com.hellomaven.quickstart.App</groupId>
                <artifactId>hello</artifactId>
              </weaveDependency>
            </weaveDependencies>
          </configuration>
          <executions>
            <execution>
              <phase>process-sources</phase>
              <goals>
                <goal>compile</goal>
                <goal>test-compile</goal>
              </goals>
            </execution>
          </executions>
          <dependencies>
            <dependency>
              <groupId>org.aspectj</groupId>
              <artifactId>aspectjrt</artifactId>
              <version>${aspectj.version}</version>
            </dependency>
            <dependency>
              <groupId>org.aspectj</groupId>
              <artifactId>aspectjtools</artifactId>
              <version>${aspectj.version}</version>
            </dependency>
          </dependencies>
        </plugin>

        <plugin>
          <groupId>org.codehaus.mojo</groupId>
          <artifactId>exec-maven-plugin</artifactId>
          <version>1.3</version>
          <configuration>
            <mainClass>com.hellomaven.quickstart</mainClass>
          </configuration>
        </plugin>

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

App.java

package com.hellomaven.quickstart;

public class App {
    public static void main(String[] args) {
        hello("World");
    }
    
    public static void hello(String world) {
        System.out.println("Hello "   world);
    }
}

AppAspect.java

package com.hellomaven.quickstart;

import org.aspectj.lang.annotation.*;

@Aspect
public class AppAspect {
    
    @Before("execution(public static void hello(..))")
    public void testAspectBefore() {
        System.out.println("Before ok.");
    }
}

CodePudding user response：

Wherever and in whichever way you are running your code, you simply need to add -javaagent:/path/to/aspectjweaver.jar to the Java command line. Furthermore, for LTW you need an aop.xml in the right place. For Maven that means:

aop.xml should be located in src/main/resources.
If you need LTW in a JUnit test or so, you need to add the -javaagent parameter to your Surefire plugin (unit tests) or Failsafe plugin (integration tests) configuration.
If you want to start your compiled program using Exec Maven plugin, as seems to be the case, you need to add the -javaagent parameter to the plugin configuration there, too.

Outside of Maven, again you need to add -javaagent to the command line.

Sorry for the generic answer, but it is just a reflection of your generic question. If you have a more precise follow-up question, you can comment on this answer.

Some resources: