This tutorial will be very interesting. Last week I was working on a Java Project which requires me to have list of Classes from .jar file. With the help of JarEntry and JarInputStream utility I was able to extract all classes from inside of .jar file.
JarInputStream creates a new JarInputStream and reads the optional manifest. If a manifest is present, also attempts to verify the signatures if the JarInputStream is signed.
Below solution will also work for your if you have any of below query:
- In Java – How to find a class somewhere inside dozens of JAR files
- How to get names of classes inside a jar file?
- Looking for a Java class in a set of JARs with find
Java Reflection Tutorial: How To Use Reflection To Call Java Method At Runtime
Let’s get started. We will perform below steps.
- Create class
CrunchifyFindClassesFromJar.java - Create utility method called
getCrunchifyClassNamesFromJar(String jarFileName) - Iterate through nextJarEntry and if found remove .class from name add it to JSON list
- Print JSONObject containing above class list
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package com.crunchify.tutorial; import java.io.FileInputStream; import java.util.jar.JarEntry; import java.util.jar.JarInputStream; import org.json.JSONArray; import org.json.JSONObject; /** * @author Crunchify.com * */ public class CrunchifyFindClassesFromJar { @SuppressWarnings("resource") public static JSONObject getCrunchifyClassNamesFromJar(String crunchifyJarName) { JSONArray listofClasses = new JSONArray(); JSONObject crunchifyObject = new JSONObject(); try { JarInputStream crunchifyJarFile = new JarInputStream(new FileInputStream(crunchifyJarName)); JarEntry crunchifyJar; while (true) { crunchifyJar = crunchifyJarFile.getNextJarEntry(); if (crunchifyJar == null) { break; } if ((crunchifyJar.getName().endsWith(".class"))) { String className = crunchifyJar.getName().replaceAll("/", "\\."); String myClass = className.substring(0, className.lastIndexOf('.')); listofClasses.put(myClass); } } crunchifyObject.put("Jar File Name", crunchifyJarName); crunchifyObject.put("List of Class", listofClasses); } catch (Exception e) { System.out.println("Oops.. Encounter an issue while parsing jar" + e.toString()); } return crunchifyObject; } public static void main(String[] args) { JSONObject myList = getCrunchifyClassNamesFromJar("/Users/<username>/Documents/javax.servlet.jsp.jar"); System.out.println(myList); } } |
Result:
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{ "List of Class": [ "javax.el.ArrayELResolver", "javax.el.BeanELResolver$BeanProperties", "javax.el.BeanELResolver$BeanProperty", "javax.el.BeanELResolver", "javax.el.CompositeELResolver$CompositeIterator", "javax.el.CompositeELResolver", "javax.el.ELContext", "javax.el.ELContextEvent", ..... ..... so many more... ], "Jar File Name": "/Users/<username>/Documents/javax.servlet.jsp.jar" } |
Bonus point:
Check out how to find if particular jar contains specific method.
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try { Class<?> crunchifyClass = Class.forName(className); Method main = crunchifyClass.getDeclaredMethod("yourMethodName"); main.invoke(null); } catch (Exception e) { e.printStackTrace(); } |
Hope this mini utility will help if you want to quickly achieve the same goal. Feel free to use it in your production project.
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