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DDDplus Framework Dynamic Plugin Jar Support
There is a newer version: 2.1.1
/*
 * Copyright DDDplus Authors.
 *
 * Licensed under the Apache License version 2.0, available at http://www.apache.org/licenses/LICENSE-2.0
 */
package io.github.dddplus.runtime.registry;

import lombok.extern.slf4j.Slf4j;

import java.io.File;
import java.io.IOException;
import java.lang.annotation.Annotation;
import java.util.*;
import java.util.jar.JarEntry;
import java.util.jar.JarFile;

@Slf4j
final class JarUtils {

    private JarUtils() {}

    static Map, List> loadClassWithAnnotations(
            String path, List> annotations, String startWith, ClassLoader classLoader) throws Throwable {
        Map, List> result = new HashMap<>();
        List filteredClassNames = filter(getAllClasses(path), startWith);
        for (String className : filteredClassNames) {
            log.debug("loading {} with {}", className, classLoader);
            // 把.class文件中的二进制数据读入堆里的Class对象
            Class clazz = classLoader.loadClass(className);
            // 先load class才能获取其注解
            for (Class annotation : annotations) {
                Annotation clazzAnnotation = clazz.getAnnotation(annotation);
                if (clazzAnnotation == null) {
                    // 该Class没有该注解
                    continue;
                }

                log.debug("{} has class of {}", annotation, className);
                List annotationClassList = result.get(annotation);
                if (annotationClassList == null) {
                    annotationClassList = new ArrayList<>();
                    result.put(annotation, annotationClassList);
                }

                annotationClassList.add(clazz);
            }
        }

        return result;
    }

    static  T loadBeanWithType(ClassLoader classLoader, String path, Class beanType) throws Throwable {
        JarFile jar = new JarFile(new File(path));
        Enumeration entries = jar.entries();
        while (entries.hasMoreElements()) {
            JarEntry entry = (JarEntry) entries.nextElement();
            String className = getClassName(entry);
            if (className == null || className.isEmpty()) {
                // not a class. e,g. META-INF
                continue;
            }

            Class clazz = classLoader.loadClass(className);
            if (!beanType.isAssignableFrom(clazz)) {
                continue;
            }

            // 自己创建实例，而不通过Spring BeanFactory创建
            return (T) clazz.newInstance();
        }

        // not found
        return null;
    }

    private static String getClassName(JarEntry jarEntry) {
        String jarName = jarEntry.getName();
        if (!jarName.endsWith(".class")) {
            return null;
        } else {
            if (jarName.charAt(0) == 47) {
                jarName = jarName.substring(1);
            }

            jarName = jarName.replace("/", ".");
            return jarName.substring(0, jarName.length() - 6);
        }
    }

    private static List getAllClasses(String path) throws IOException {
        ArrayList classNames = new ArrayList();
        JarFile jar = new JarFile(new File(path)); // might throw FileNotFoundException

        Enumeration entries = jar.entries();
        while (entries.hasMoreElements()) {
            JarEntry entry = (JarEntry) entries.nextElement();
            String className = getClassName(entry);
            if (className != null && className.length() > 0) {
                classNames.add(className);
            }
        }

        return classNames;
    }

    private static List filter(List names, String startWith) {
        if (startWith == null || startWith.isEmpty()) {
            return names;
        }

        List result = new ArrayList(names.size());
        for (String name : names) {
            if (name == null) {
                continue;
            }

            if (name.startsWith(startWith)) {
                result.add(name);
            }
        }

        return result;
    }

}