strange exception of “java.lang.NoClassDefFoundError: javassist/ClassPath” when running with commandline

Question

I hava a agent class, it simply print two lines before and after another project's main() method. The agent class is as follows

public class Agent {

static String packageName = "xxx.hello.world";

public static void premain(String agentArgs, Instrumentation inst) {


    inst.addTransformer((classLoader, s, aClass, protectionDomain, bytes) -> {
        byte[] transformed = null;
        CtClass cl = null;
        try {
            ClassPool pool = new ClassPool();
            pool.insertClassPath(new LoaderClassPath(Thread.currentThread().getContextClassLoader()));
            pool.importPackage(packageName);
            cl = pool.makeClass(new ByteArrayInputStream(bytes));
            CtMethod[] methods = cl.getDeclaredMethods();

            for (CtMethod method : methods) {
                if ("main".equals(method.getName())) {
                    method.insertBefore("System.out.println(\"<-----------before------->\");");
                    method.insertAfter("System.out.println(\"<-----------end------->\");");
                }
            }
            transformed = cl.toBytecode();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (cl != null) {
                cl.detach();
            }
        }
        return transformed;

    });
}}

And I have another project named as "HelloWorld", it simply print "Hi, i am in main()" in it's main method. The HelloWorld.class is as follows

public class HelloWorld {
public static void main(String[] args) {
    System.out.println("Hi, i am in main()");
}

Then I package the agent as a jar named as "agent.jar", and add "-javaagent:xxx/yyy/agent.jar" to vmoptions in IDEA, like this

After that, when I run the hello-world, I get what i want like

<-----------before------->
 Hi, i am in main()
<-----------end------->

However, when I try to run the hello-world as a jar like "hello-world.jar" in command line like

java -javaagent:xxx/yyy/agent.jar -jar hello-world.jar

I get a strange error like

Exception in thread "main" java.lang.NoClassDefFoundError: javassist/ClassPath
    at java.lang.Class.getDeclaredMethods0(Native Method)
    at java.lang.Class.privateGetDeclaredMethods(Unknown Source)
    at java.lang.Class.getDeclaredMethod(Unknown Source)
    at sun.instrument.InstrumentationImpl.loadClassAndStartAgent(Unknown Source)
    at sun.instrument.InstrumentationImpl.loadClassAndCallPremain(Unknown Source)
Caused by: java.lang.ClassNotFoundException: javassist.ClassPath
    at java.net.URLClassLoader.findClass(Unknown Source)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    ... 5 more

It is quite strange because I think the two ways (in IDEA and in command line) are the same. And when i check the hello-world.jar, i can see the javassist/ClassPath.class.

Can any tell me why and how to fix this problem?

Thanks!

Answer 1

I faced the same issue, you can refer to the pom.xml below, and see the difference with yours in hello-world project.

<?xml version="1.0" encoding="UTF-8"?>
<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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.richard</groupId>
    <artifactId>my-agent-test</artifactId>
    <version>1.0-SNAPSHOT</version>

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


    <build>
        <plugins>
            <plugin>
                <artifactId>maven-assembly-plugin</artifactId>
                <version>2.4</version>
                <configuration>
                    <descriptorRefs>
                        <descriptorRef>jar-with-dependencies</descriptorRef>
                    </descriptorRefs>
                    <archive>
                        <manifest>
                            <mainClass>com.richard.Main</mainClass>
                        </manifest>
                    </archive>
                </configuration>
                <executions>
                    <execution>
                        <id>make-assembly</id>
                        <phase>package</phase>
                        <goals>
                            <goal>single</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>

    <dependencies>
        <dependency>
            <groupId>org.javassist</groupId>
            <artifactId>javassist</artifactId>
            <version>3.20.0-GA</version>
        </dependency>
    </dependencies>

</project>