Spring boot jar loading

Question

By default if we add jar plugin as dependency to our spring boot app, spring can load these dependenies. But how can I configure spring to load my custom jar plugin from custom paths.

Answer 1

If you want to load a custom jar from local, you may want to try through the "URLClassLoader".

Here is a simple example of loading a class from jar file.

@Test
public void demo() throws Exception {
    String location = "the-path-to-your-jar";
    Path path = Paths.get(location);
    URLClassLoader classLoader = new URLClassLoader(new URL[]{path.toUri().toURL()});
    classLoader.loadClass("your-class-full-qulify-name");
}

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Here is update.

If you need to load all classes, then you can use JarFile to find all classes in a jar.

public Set<String> getClassNamesFromJarFile(File file) throws IOException {
    Set<String> classNames = new HashSet<>();
    try (JarFile jarFile = new JarFile(file)) {
        Enumeration<JarEntry> entries = jarFile.entries();
        while (entries.hasMoreElements()) {
            JarEntry jarEntry = entries.nextElement();
            if (jarEntry.isDirectory()) {
                continue;
            }
            String jarName = jarEntry.getName();
            if (jarName.endsWith(".class")) {
                String className = jarName.replace("/", ".");
                classNames.add(className);
            }
        }
        return classNames;
    }
}