{"id":8714,"date":"2016-08-18T13:21:39","date_gmt":"2016-08-18T11:21:39","guid":{"rendered":"https:\/\/www.dbi-services.com\/blog\/java-reflection-get-classes-and-packages-names-from-a-root-package-within-a-custom-urlclassloader\/"},"modified":"2016-08-18T13:21:39","modified_gmt":"2016-08-18T11:21:39","slug":"java-reflection-get-classes-and-packages-names-from-a-root-package-within-a-custom-urlclassloader","status":"publish","type":"post","link":"https:\/\/www.dbi-services.com\/blog\/java-reflection-get-classes-and-packages-names-from-a-root-package-within-a-custom-urlclassloader\/","title":{"rendered":"Java reflection: Get classes and packages names from a root package within a custom URLClassloader"},"content":{"rendered":"

\"\"<\/p>\n

I have got a case for which I needed to use a custom Classloader, in order to find the list of classes and packages available across several software plugins materialized by a set of jar files. These jar files are intended to be located inside a particular place.<\/p>\n

After googling, some solutions invited us to deploy external libraries. But I was not interested to manage another lib in my soft just for that purpose.
\nSo, the solution was to recover all jars from the specific Classloader and loop on them in order to find out the classes and packages I was looking for.<\/p>\n

This blog post is an extension of a previous one, that only looked for classes within the JVM context Classloader:<\/p>\n

http:\/\/dbi-services.com\/blog\/java-get-class-names-from-package-string-in-classpath\/<\/a><\/p>\n

 <\/p>\n

This example now, shows how to initiate a new child Classloader, to work with, and extract packages names in addition to Classes list available inside a root package name.
\nFollowing, you will see a complete Java class resolving this issue:<\/p>\n

 <\/p>\n

import<\/b><\/span> java.io.File;<\/span><\/span>\nimport<\/b><\/span> java.io.FileFilter;<\/span><\/span>\nimport<\/b><\/span> java.net.URISyntaxException;<\/span><\/span>\nimport<\/b><\/span> java.net.URL;<\/span><\/span>\nimport<\/b><\/span> java.net.URLClassLoader;<\/span><\/span>\nimport<\/b><\/span> java.nio.file.Path;<\/span><\/span>\nimport<\/b><\/span> java.nio.file.Paths;<\/span><\/span>\nimport<\/b><\/span> java.util.ArrayList;<\/span><\/span>\nimport<\/b><\/span> java.util.Enumeration;<\/span><\/span>\nimport<\/b><\/span> java.util.TreeMap;<\/span><\/span>\nimport<\/b><\/span> java.util.TreeSet;<\/span><\/span>\nimport<\/b><\/span> java.util.jar.JarEntry;<\/span><\/span>\nimport<\/b><\/span> java.util.jar.JarFile;<\/span><\/span>\n\n\/**<\/span>\n\u00a0<\/span>*<\/b><\/span> @author<\/b><\/span> Philippe Schweitzer, dbi services Switzerland<\/b><\/span><\/span>\n\u00a0<\/span>*<\/b><\/span><\/span>\n\u00a0<\/span>*<\/b><\/span> It is a Class that demonstrates how to list Classes and Packages from a given<\/span><\/span>\n\u00a0<\/span>*<\/b><\/span> root package name.<\/span><\/span>\n\u00a0<\/span>*<\/b><\/span><\/span>\n\u00a0<\/span>*<\/b><\/span> This class uses a specific Classloader in order to lookup into jar files<\/span><\/span>\n\u00a0<\/span>*<\/b><\/span> located at a dedicated place (and not in all JavaSE library ).<\/span><\/span>\n\u00a0<\/span>*<\/b><\/span><\/span>\n\u00a0*\/<\/span>\npublic<\/b><\/span> class<\/b><\/span> RessourceFinderExample {<\/span>\n\n    \/* Root package name *\/<\/span><\/span>\n    private<\/b><\/span> static<\/b><\/span> final<\/b><\/span> String<\/b><\/span> packageName = \"YOUR PACKAGE NAME\"<\/span>;<\/span>\n\n    \/* Paths list to jar files *\/<\/span><\/span>\n    private<\/b><\/span> static<\/b><\/span> final<\/b><\/span> String<\/b><\/span>[] classPaths = {\"plugins\"<\/span>, \".\"<\/span>, \"dist\"<\/span>};<\/span>\n\n    \/**<\/span><\/span>\n\u00a0\u00a0\u00a0\u00a0\u00a0<\/span>*<\/b><\/span> Main method<\/span>,<\/b><\/span> it creates the Classloader and displays a consolidated<\/span><\/span>\n\u00a0\u00a0\u00a0\u00a0\u00a0<\/span>*<\/b><\/span> result.<\/span><\/span>\n\u00a0\u00a0\u00a0\u00a0\u00a0<\/span>*<\/b><\/span><\/span>\n\u00a0\u00a0\u00a0\u00a0\u00a0<\/span>*<\/b><\/span> @param<\/b><\/span> args no argument required<\/span><\/span>\n\u00a0\u00a0\u00a0\u00a0\u00a0*\/<\/span>\n    public<\/b><\/span> static<\/b><\/span> void<\/b><\/span> main(String<\/b><\/span> args[]) {<\/span>\n\n        URLClassLoader cl = new<\/b><\/span> URLClassLoader(findJarURLsInClasspath(), Thread<\/b><\/span>.currentThread().getContextClassLoader());<\/span>\n\n        System<\/b><\/span>.out.println(\"\"<\/span>);<\/span>\n\n        TreeSet<String<\/b><\/span>> packages = RessourceFinderExample.getPackageFromPackage(packageName, cl);<\/span>\n\n        System<\/b><\/span>.out.println(\"\"<\/span>);<\/span>\n        System<\/b><\/span>.out.println(\"-- CONSOLIDATED  RESULT --\"<\/span>);<\/span>\n        System<\/b><\/span>.out.println(\"\"<\/span>);<\/span>\n\n        for<\/b><\/span> (String<\/b><\/span> packageString : packages) {<\/span>\n            System<\/b><\/span>.out.println(\"   PACKAGE : \"<\/span> + packageString);<\/span>\n        }<\/span>\n\n        System<\/b><\/span>.out.println(\"\"<\/span>);<\/span>\n        System<\/b><\/span>.out.println(\"--------------------------\"<\/span>);<\/span>\n        System<\/b><\/span>.out.println(\"\"<\/span>);<\/span>\n\n        TreeMap<String<\/b><\/span>, Class<\/b><\/span>> classes = RessourceFinderExample.getClassesFromPackage(packageName, cl);<\/span>\n\n        System<\/b><\/span>.out.println(\"\"<\/span>);<\/span>\n        System<\/b><\/span>.out.println(\"-- CONSOLIDATED  RESULT --\"<\/span>);<\/span>\n        System<\/b><\/span>.out.println(\"\"<\/span>);<\/span>\n\n        for<\/b><\/span> (Class<\/b><\/span> c : classes.values()) {<\/span>\n            System<\/b><\/span>.out.println(\"   CLASS   : \"<\/span> + packageName + \".\"<\/span> + c.getCanonicalName());<\/span>\n        }<\/span>\n\n        System<\/b><\/span>.out.println(\"\"<\/span>);<\/span>\n        System<\/b><\/span>.out.println(\"--------------------------\"<\/span>);<\/span>\n        System<\/b><\/span>.out.println(\"\"<\/span>);<\/span>\n    }<\/span>\n\n    \/**<\/span><\/span>\n\u00a0\u00a0\u00a0\u00a0\u00a0<\/span>*<\/b><\/span> Method that finds all jar files available in given dedicated classpath<\/span><\/span>\n\u00a0\u00a0\u00a0\u00a0\u00a0<\/span>*<\/b><\/span> places. It serves for an URLClassloader initialization.<\/span><\/span>\n\u00a0\u00a0\u00a0\u00a0\u00a0<\/span>*<\/b><\/span><\/span>\n\u00a0\u00a0\u00a0\u00a0\u00a0<\/span>*<\/b><\/span> @return<\/b><\/span> List of jar files URLs<\/span><\/span>\n\u00a0\u00a0\u00a0\u00a0\u00a0*\/<\/span>\n    private<\/b><\/span> static<\/b><\/span> URL<\/b><\/span>[] findJarURLsInClasspath() {<\/span>\n        URL<\/b><\/span> url;<\/span>\n\n        ArrayList<URL<\/b><\/span>> jarURLs = new<\/b><\/span> ArrayList();<\/span>\n\n        for<\/b><\/span> (String<\/b><\/span> path : classPaths) {<\/span>\n\n            File<\/b><\/span>[] jars = new<\/b><\/span> File<\/b><\/span>(path).listFiles(new<\/b><\/span> FileFilter() {<\/span>\n                public<\/b><\/span> boolean<\/b><\/span> accept(File<\/b><\/span> pathname) {<\/span>\n\n                    return<\/b><\/span> pathname.getName().toLowerCase().endsWith(\".jar\"<\/span>);<\/span>\n                }<\/span>\n            });<\/span>\n\n            if<\/b><\/span> (jars != null<\/b><\/span>) {<\/span>\n                for<\/b><\/span> (int<\/b><\/span> i = 0; i < jars.length; i++) {<\/span>\n                    try<\/b><\/span> {<\/span>\n                        System<\/b><\/span>.out.println(\"JAR Path: \"<\/span> + jars[i].getAbsolutePath());<\/span>\n                        url = jars[i].toURI().toURL();<\/span>\n\n                        jarURLs.add(url);<\/span>\n\n                    } catch<\/b><\/span> (Exception<\/b><\/span> e) {<\/span>\n\n                    }<\/span>\n                }<\/span>\n            }<\/span>\n        }<\/span>\n\n        URL<\/b><\/span>[] urls = jarURLs.toArray(new<\/b><\/span> URL<\/b><\/span>[0]);<\/span>\n        return<\/b><\/span> urls;<\/span>\n    }<\/span>\n\n    \/**<\/span><\/span>\n\u00a0\u00a0\u00a0\u00a0\u00a0<\/span>*<\/b><\/span> Method that returns all jar files registered in the given URLClassloader<\/span><\/span>\n\u00a0\u00a0\u00a0\u00a0\u00a0<\/span>*<\/b><\/span> and which are present in dedicated classpath places.<\/span><\/span>\n\u00a0\u00a0\u00a0\u00a0\u00a0<\/span>*<\/b><\/span><\/span>\n\u00a0\u00a0\u00a0\u00a0\u00a0<\/span>*<\/b><\/span> @return<\/b><\/span> List of jar files URLs<\/span><\/span>\n\u00a0\u00a0\u00a0\u00a0\u00a0*\/<\/span>\n    private<\/b><\/span> static<\/b><\/span> URL<\/b><\/span>[] getJarURLs(URLClassLoader cl) {<\/span>\n        URL<\/b><\/span>[] result = cl.getURLs();<\/span>\n        ArrayList<URL<\/b><\/span>> urls = new<\/b><\/span> ArrayList();<\/span>\n\n        for<\/b><\/span> (URL<\/b><\/span> url : result) {<\/span>\n\n            try<\/b><\/span> {<\/span>\n                Path jarPath = Paths.get(url.toURI());<\/span>\n\n                for<\/b><\/span> (String<\/b><\/span> classPathString : classPaths) {<\/span>\n\n                    Path classPath = Paths.get(classPathString).toAbsolutePath();<\/span>\n\n                    if<\/b><\/span> (jarPath.startsWith(classPath)) {<\/span>\n                        urls.add(url);<\/span>\n                    }<\/span>\n                }<\/span>\n\n            } catch<\/b><\/span> (URISyntaxException ex) {<\/span>\n            }<\/span>\n        }<\/span>\n\n        result = new<\/b><\/span> URL<\/b><\/span>[urls.size()];<\/span>\n        result = urls.toArray(result);<\/span>\n\n        return<\/b><\/span> result;<\/span>\n    }<\/span>\n\n    \/**<\/span><\/span>\n\u00a0\u00a0\u00a0\u00a0\u00a0<\/span>*<\/b><\/span> Method that returns all classes available underneath a given package<\/span><\/span>\n\u00a0\u00a0\u00a0\u00a0\u00a0<\/span>*<\/b><\/span> name.<\/span><\/span>\n\u00a0\u00a0\u00a0\u00a0\u00a0<\/span>*<\/b><\/span><\/span>\n\u00a0\u00a0\u00a0\u00a0\u00a0<\/span>*<\/b><\/span> @return<\/b><\/span> Set of Classes<\/span><\/span>\n\u00a0\u00a0\u00a0\u00a0\u00a0*\/<\/span>\n    private<\/b><\/span> static<\/b><\/span> TreeMap<String<\/b><\/span>, Class<\/b><\/span>> getClassesFromPackage(String<\/b><\/span> pckgname, URLClassLoader cl) {<\/span>\n        TreeMap<String<\/b><\/span>, Class<\/b><\/span>> result = new<\/b><\/span> TreeMap();<\/span>\n        ArrayList<File<\/b><\/span>> files = new<\/b><\/span> ArrayList();<\/span>\n\n        for<\/b><\/span> (URL<\/b><\/span> jarURL : getJarURLs(cl)) {<\/span>\n            getClassesInSamePackageFromJar(result, pckgname, jarURL.getPath(), cl);<\/span>\n        }<\/span>\n\n        return<\/b><\/span> result;<\/span>\n    }<\/span>\n\n    \/**<\/span><\/span>\n\u00a0\u00a0\u00a0\u00a0\u00a0<\/span>*<\/b><\/span> Method that fills TreeMap with all classes available in a particular jar<\/span><\/span>\n\u00a0\u00a0\u00a0\u00a0\u00a0<\/span>*<\/b><\/span> file<\/span>,<\/b><\/span> underneath a given package name.<\/span><\/span>\n\u00a0\u00a0\u00a0\u00a0\u00a0<\/span>*<\/b><\/span><\/span>\n\u00a0\u00a0\u00a0\u00a0\u00a0*\/<\/span>\n    private<\/b><\/span> static<\/b><\/span> void<\/b><\/span> getClassesInSamePackageFromJar(TreeMap<String<\/b><\/span>, Class<\/b><\/span>> result, String<\/b><\/span> packageName, String<\/b><\/span> jarPath, URLClassLoader cl) {<\/span>\n        JarFile jarFile = null<\/b><\/span>;<\/span>\n        try<\/b><\/span> {<\/span>\n\n            System<\/b><\/span>.out.println(\"\"<\/span>);<\/span>\n            System<\/b><\/span>.out.println(\"** IN JAR : \"<\/span> + jarPath);<\/span>\n            jarFile = new<\/b><\/span> JarFile(jarPath);<\/span>\n\n            Enumeration<\/b><\/span><JarEntry> en = jarFile.entries();<\/span>\n            while<\/b><\/span> (en.hasMoreElements()) {<\/span>\n                JarEntry entry = en.nextElement();<\/span>\n                String<\/b><\/span> entryName = entry.getName();<\/span>\n\n                packageName = packageName.replace('.'<\/span>, '\/'<\/span>);<\/span>\n\n                if<\/b><\/span> (entryName != null<\/b><\/span> && entryName.endsWith(\".class\"<\/span>) && entryName.startsWith(packageName) && !entryName.substring(packageName.length() + 1).contains(\"\/\"<\/span>)) {<\/span>\n\n                    try<\/b><\/span> {<\/span>\n                        Class<\/b><\/span><?> entryClass = cl.loadClass(entryName.substring(0, entryName.length() - 6).replace('\/'<\/span>, '.'<\/span>));<\/span>\n                        if<\/b><\/span> (entryClass != null<\/b><\/span>) {<\/span>\n                            result.put(entryClass.getCanonicalName(), entryClass);<\/span>\n                            System<\/b><\/span>.out.println(\"   CLASS   : \"<\/span> + packageName + \".\"<\/span> + entryClass.getCanonicalName());<\/span>\n                        }<\/span>\n                    } catch<\/b><\/span> (Throwable<\/b><\/span> e) {<\/span>\n\/\/                        System.err.println(\"Error instanciating: \" + entryName + \" \" + e.toString());<\/span>\n                    }<\/span>\n                }<\/span>\n            }<\/span>\n        } catch<\/b><\/span> (Exception<\/b><\/span> e) {<\/span>\n        } finally<\/b><\/span> {<\/span>\n            try<\/b><\/span> {<\/span>\n                if<\/b><\/span> (jarFile != null<\/b><\/span>) {<\/span>\n                    jarFile.close();<\/span>\n                }<\/span>\n            } catch<\/b><\/span> (Exception<\/b><\/span> e) {<\/span>\n            }<\/span>\n        }<\/span>\n    }<\/span>\n\n    \/**<\/span><\/span>\n\u00a0\u00a0\u00a0\u00a0\u00a0<\/span>*<\/b><\/span> Method that returns all package names underneath a given root package<\/span><\/span>\n\u00a0\u00a0\u00a0\u00a0\u00a0<\/span>*<\/b><\/span> name.<\/span><\/span>\n\u00a0\u00a0\u00a0\u00a0\u00a0<\/span>*<\/b><\/span><\/span>\n\u00a0\u00a0\u00a0\u00a0\u00a0<\/span>*<\/b><\/span> @return<\/b><\/span> Set of Classes<\/span><\/span>\n\u00a0\u00a0\u00a0\u00a0\u00a0*\/<\/span>\n    private<\/b><\/span> static<\/b><\/span> TreeSet<String<\/b><\/span>> getPackageFromPackage(String<\/b><\/span> pckgname, URLClassLoader cl) {<\/span>\n        TreeSet<String<\/b><\/span>> result = new<\/b><\/span> TreeSet();<\/span>\n\n        for<\/b><\/span> (URL<\/b><\/span> jarURL : getJarURLs(cl)) {<\/span>\n            getPackageInPackageFromJar(result, pckgname, jarURL.getPath(), cl);<\/span>\n        }<\/span>\n\n        return<\/b><\/span> result;<\/span>\n    }<\/span>\n\n    \/**<\/span><\/span>\n\u00a0\u00a0\u00a0\u00a0\u00a0<\/span>*<\/b><\/span> Method that fills TreeMap with all package names in a particular jar<\/span><\/span>\n\u00a0\u00a0\u00a0\u00a0\u00a0<\/span>*<\/b><\/span> file<\/span>,<\/b><\/span> underneath a given root package name.<\/span><\/span>\n\u00a0\u00a0\u00a0\u00a0\u00a0<\/span>*<\/b><\/span><\/span>\n\u00a0\u00a0\u00a0\u00a0\u00a0*\/<\/span>\n    private<\/b><\/span> static<\/b><\/span> void<\/b><\/span> getPackageInPackageFromJar(TreeSet<String<\/b><\/span>> result, String<\/b><\/span> packageName, String<\/b><\/span> jarPath, URLClassLoader cl) {<\/span>\n        JarFile jarFile = null<\/b><\/span>;<\/span>\n        try<\/b><\/span> {<\/span>\n            System<\/b><\/span>.out.println(\"\"<\/span>);<\/span>\n            System<\/b><\/span>.out.println(\"** IN JAR : \"<\/span> + jarPath);<\/span>\n\n            jarFile = new<\/b><\/span> JarFile(jarPath);<\/span>\n\n            Enumeration<\/b><\/span><JarEntry> en = jarFile.entries();<\/span>\n            while<\/b><\/span> (en.hasMoreElements()) {<\/span>\n                JarEntry entry = en.nextElement();<\/span>\n                String<\/b><\/span> entryName = entry.getName();<\/span>\n\n                packageName = packageName.replace('.'<\/span>, '\/'<\/span>);<\/span>\n\n                if<\/b><\/span> (entryName != null<\/b><\/span> && entryName.endsWith(\"\/\"<\/span>) && entryName.startsWith(packageName + \"\/\"<\/span>)) {<\/span>\n\n                    try<\/b><\/span> {<\/span>\n                        String<\/b><\/span> packageEntryName = entryName.substring(packageName.length() + 1);<\/span>\n                        packageEntryName = packageEntryName.substring(0, packageEntryName.indexOf(\"\/\"<\/span>));<\/span>\n\n                        result.add(packageName.replace('\/'<\/span>, '.'<\/span>) + \".\"<\/span> + packageEntryName);<\/span>\n\n                        System<\/b><\/span>.out.println(\"   PACKAGE : \"<\/span> + packageName.replace('\/'<\/span>, '.'<\/span>) + \".\"<\/span> + packageEntryName);<\/span>\n                    } catch<\/b><\/span> (Throwable<\/b><\/span> e) {<\/span>\n                    }<\/span>\n                }<\/span>\n            }<\/span>\n        } catch<\/b><\/span> (Exception<\/b><\/span> e) {<\/span>\n        } finally<\/b><\/span> {<\/span>\n            try<\/b><\/span> {<\/span>\n                if<\/b><\/span> (jarFile != null<\/b><\/span>) {<\/span>\n                    jarFile.close();<\/span>\n                }<\/span>\n            } catch<\/b><\/span> (Exception<\/b><\/span> e) {<\/span>\n            }<\/span>\n        }<\/span>\n    }<\/span><\/pre>\n
\n","protected":false},"excerpt":{"rendered":"
I have got a case for which I needed to use a custom Classloader, in order to find the list of classes and packages available across several software plugins materialized by a set of jar files. These jar files are intended to be located inside a particular place. After googling, some solutions invited us to […]<\/p>\n","protected":false},"author":40,"featured_media":4051,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[368],"tags":[],"type_dbi":[],"class_list":["post-8714","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-development-performance"],"acf":[],"yoast_head":"\nJava reflection: Get classes and packages names from a root package within a custom URLClassloader - dbi Blog<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.dbi-services.com\/blog\/java-reflection-get-classes-and-packages-names-from-a-root-package-within-a-custom-urlclassloader\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Java reflection: Get classes and packages names from a root package within a custom URLClassloader\" \/>\n<meta property=\"og:description\" content=\"I have got a case for which I needed to use a custom Classloader, in order to find the list of classes and packages available across several software plugins materialized by a set of jar files. These jar files are intended to be located inside a particular place. 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