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How to read class name and its method with its signature from the jar file in java.

1 Spice up
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I almost deleted this as spam with the “hurry” title and the all-caps. Can you tell us why the urgency?

2 Spice ups
3

Need to get the answer asap.

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4

Did you try googling ‘How to read class name and its method with its signature from the jar file in java’? Because I got what looked like a pretty valid response in the ‘ai overview’. Although I haven’t looked at java in decades…

====

import java.io.IOException;
import java.util.Enumeration;
import java.util.jar.JarEntry;
import java.util.jar.JarFile;

public class ReadJar {

    public static void main(String[] args) throws IOException {
        String jarFilePath = "path/to/your/jarfile.jar";

        try (JarFile jarFile = new JarFile(jarFilePath)) {
            Enumeration<JarEntry> entries = jarFile.entries();

            while (entries.hasMoreElements()) {
                JarEntry entry = entries.nextElement();

                if (entry.getName().endsWith(".class")) {
                    String className = entry.getName().replace("/", ".").replace(".class", "");

                    try {
                        Class<?> clazz = Class.forName(className);

                        System.out.println("Class: " + className);

                        for (java.lang.reflect.Method method : clazz.getDeclaredMethods()) {
                            System.out.println("  Method: " + method.getName() + " " + method.toGenericString());
                        }

                    } catch (ClassNotFoundException e) {
                        System.err.println("Error loading class: " + className);
                        e.printStackTrace();
                    }
                }
            }
        }
    }
}

=====

3 Spice ups
5

And if that code is poor, there are a couple of good links to basically same question, saw one in stackoverflow and one, of course, in spiceworks…

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6

Its not poor code. But, it throws an error “class not found” exception.

But, that jar file contains the class

7

A forum isn’t the place for emergencies, you wouldn’t email the police if you was being burgled.

Perhaps you can add some background as to why this is a hurry, did you not complete your homework for school, did you make a change that broke something?

2 Spice ups
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Take care of my question not the emergency and then answer

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Don’t come here demanding someone else fixes your issue. I am simply advising you that if your issue is of an urgent nature, a forum is not the right place.

Remember, you are here because you need help, not the other way round so have some respect.

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Sure. I am not talking disrespectful.

I need a solution because I tried in many ways.

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And what code do you have, is this in Windows, Linux or another OS?

Do you have all required pre requisites to run the code?

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I tried this,

    public static void main(String[] args) throws IOException, ClassNotFoundException {
    String jarPath = "/Users/Practice/lib/Example.jar"; 
    List<String> classNames = new ArrayList<String>();
    ZipInputStream zip = new ZipInputStream(new FileInputStream(jarPath));
    for (ZipEntry entry = zip.getNextEntry(); entry != null; entry = zip.getNextEntry()) {
        if (!entry.isDirectory() && entry.getName().endsWith(".class")) {
            String className = entry.getName().replace('/', '.');
            String[] classNamess = className.split("\\.");
            String formattedClassName = "";
            for(int i=0;i<classNamess.length-1;i++)
            {
                formattedClassName += classNamess[i];
                if(!(i==classNamess.length-2))
                {
                    formattedClassName += ".";
                }
            }
            System.out.println(formattedClassName);
        }
    }
}

Environment: Mac
Have all pre requisites to run

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And in this above code, I tried to get only the class name (with package).

Now, my question is to get the method and its signature

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I am no coder, so ensure you test this first either in a virtual environment or against something you have backups of.

import java.io.*;
import java.util.*;
import java.util.jar.*;
import java.util.zip.*;
import java.lang.reflect.*;

public class Main {
    public static void main(String[] args) throws IOException, ClassNotFoundException {
        String jarPath = "/Users/Practice/lib/Example.jar"; 
        List<String> classNames = new ArrayList<String>();
        ZipInputStream zip = new ZipInputStream(new FileInputStream(jarPath));
        for (ZipEntry entry = zip.getNextEntry(); entry != null; entry = zip.getNextEntry()) {
            if (!entry.isDirectory() && entry.getName().endsWith(".class")) {
                String className = entry.getName().replace('/', '.');
                className = className.substring(0, className.length() - 6); // Remove ".class"
                classNames.add(className);
            }
        }
        zip.close();

        for (String className : classNames) {
            Class<?> clazz = Class.forName(className);
            System.out.println("Class: " + clazz.getName());
            Method[] methods = clazz.getDeclaredMethods();
            for (Method method : methods) {
                System.out.println("  Method: " + method.getName());
                System.out.println("    Signature: " + method.toString());
            }
        }
    }
}
1 Spice up
15

Almost correct but have the following issue

Exception in thread “main” java.lang.ClassNotFoundException: com.example.cloudconnector.CLOUDAPPSETTINGS
at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:581)
at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:178)
at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:527)
at java.base/java.lang.Class.forName0(Native Method)
at java.base/java.lang.Class.forName(Class.java:315)
at org.example.MethodSignatureFetcher.main(MethodSignatureFetcher.java:37)

Note: I can get all class name but when I try to access the class, I receive error

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If you are getting “Class Not Found” exceptions, it’s because you haven’t imported the prerequisite package which includes the class specified in the error. For example, you will get the same type of exception errors if trying to create a variable of a String type but you fail to import the java.lang package before doing so.

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