com.cmeza.java.jar.plugin.manager.PluginClassLoader Maven / Gradle / Ivy

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package com.cmeza.java.jar.plugin.manager;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.jar.JarFile;
import java.util.zip.ZipEntry;

public final class PluginClassLoader extends ClassLoader {
    private static final Logger log = LoggerFactory.getLogger(PluginClassLoader.class);
    private final JarFile jarFile;

    public PluginClassLoader(JarFile jarFile) {
        this.jarFile = jarFile;
    }

    @Override
    public Class findClass(String name) throws ClassNotFoundException {
        log.debug("Searching named class: {}", name);
        byte[] bytes = loadClassFromFile(name);

        return defineClass(name, bytes, 0, bytes.length);
    }

    private byte[] loadClassFromFile(String fileName) throws ClassNotFoundException {
        String classFile = fileName.replace('.', '/') + ".class";
        ZipEntry entry = jarFile.getEntry(classFile);
        if (null == entry) {
            throw new ClassNotFoundException("Class not found: " + fileName);
        }

        int length;
        byte[] buffer = new byte[1024];
        ByteArrayOutputStream byteStream = new ByteArrayOutputStream();

        try (InputStream is = jarFile.getInputStream(entry)) {
            while (-1 != (length = is.read(buffer))) {
                byteStream.write(buffer, 0, length);
            }
        } catch (IOException e) {
            throw new ClassNotFoundException("Can't access class: " + fileName, e);
        }

        return byteStream.toByteArray();
    }
}