Spring boot 业务插件开发

分手后的思念是犯贱 2022-05-31 14:46 612阅读 0赞

# Spring boot 动态加载class, 注册Bean 插件开发简单实现 #

1.  使用场景  
    项目运行，在不重启服务器的前提下，动态增加业务逻辑。业务逻辑以插件的形式加入。
2.  技术分析  
    虚拟机在启动时已经把class文件加载到虚拟机，要考虑如何把外部的 class 文件加载到虚拟机中。  
    class 文件加载到虚拟机后，要考虑如何把类动态的加到 spring中，注册成bean.  
    如何调用加载到spring容器中的 bean.
3.  技术实现
    
    **外部class文件加载到JVM**

public static List<Class> LoadClass(String filePath, ClassLoader beanClassLoader) {
            List<Class> classNameList = new ArrayList<>();
            File clazzPath = new File(filePath);
            int clazzCount = 0;
            if (clazzPath.exists() && clazzPath.isDirectory()) {
                int clazzPathLen = clazzPath.getAbsolutePath().length() + 1;
                Stack<File> stack = new Stack<>();
                stack.push(clazzPath);
                while (stack.isEmpty() == false) {
                    File path = stack.pop();
                    File[] classFiles = path.listFiles(new FileFilter() {
                        public boolean accept(File pathname) {
                            return pathname.isDirectory() || pathname.getName().endsWith(".class");
                        }
                    });
                    for (File subFile : classFiles) {
                        if (subFile.isDirectory()) {
                            stack.push(subFile);
                        } else {
                            if (clazzCount++ == 0) {
                                Method method = null;
                                try {
                                    method = URLClassLoader.class.getDeclaredMethod("addURL", URL.class);
                                } catch (NoSuchMethodException e) {
                                    e.printStackTrace();
                                }
                                boolean accessible = method.isAccessible();
                                try {
                                    if (accessible == false) {
                                        method.setAccessible(true);
                                    }
                                    URLClassLoader classLoader = (URLClassLoader) beanClassLoader;
                                    try {
                                        URL url = clazzPath.toURI().toURL();
                                        method.invoke(classLoader, url);
                                    } catch (IllegalAccessException e) {
                                        e.printStackTrace();
                                    } catch (InvocationTargetException e) {
                                        e.printStackTrace();
                                    } catch (MalformedURLException e) {
                                        e.printStackTrace();
                                    }
                                } finally {
                                    method.setAccessible(accessible);
                                }
                            }
                            String className = subFile.getAbsolutePath();
                            className = className.substring(clazzPathLen, className.length() - 6);
                            className = className.replace(File.separatorChar, '.');
                            try {
                                classNameList.add(Class.forName(className));
                            } catch (ClassNotFoundException e) {
                                e.printStackTrace();
                            }
                        }
                    }
                }
            }
            return classNameList;
        }

注：filePath是外部class 文件的根目录（例如，插件包名为com.test 类为Plugin. java ,根目录为d:/aaa ,Plugin.java全目录应为：d:/aaa/com/test/Plugin. java）

**动态注册bean.**

@RequestMapping("/beanLoad")
        public String beanLoad(){
            ApplicationContext applicationContext = CommonContextUtils.getApplicationContext();
            ConfigurableApplicationContext context = (ConfigurableApplicationContext)applicationContext;
            DefaultListableBeanFactory beanFactory = (DefaultListableBeanFactory)context.getBeanFactory();
            ClassLoader beanClassLoader = beanFactory.getBeanClassLoader();
            Class aClass = ClassUtil.LoadClass("D:/classtest",beanClassLoader).get(0);
            BeanDefinitionBuilder beanDefinitionBuilder = BeanDefinitionBuilder.genericBeanDefinition(aClass);
            beanFactory.registerBeanDefinition(aClass.getName(),beanDefinitionBuilder.getRawBeanDefinition());
            Object aaa = (applicationContext.getBean(aClass.getName()));
            Method m = null;
            Method m2 = null;
            try {
                m2 = aClass.getMethod("setApplicationContext", ApplicationContext.class);
                m = aClass.getMethod("getString", null);
            } catch (NoSuchMethodException e) {
                e.printStackTrace();
            }
            Object ret = null;
            try {
                m2.invoke(aaa,applicationContext);
                ret = m.invoke(aaa, null);
            } catch (IllegalAccessException e) {
                e.printStackTrace();
            } catch (InvocationTargetException e) {
                e.printStackTrace();
            }
            return ret.toString();
        }

此处涉及一个知识点，如果取得ApplicationContext

@SuppressWarnings({ "rawtypes", "unchecked" })
    @Component
    public class CommonContextUtils implements ApplicationContextAware { 
    
        private static ApplicationContext applicationContext;
    
        public void setApplicationContext(ApplicationContext arg0)
                throws BeansException {
            applicationContext = arg0;
        }
    
        /** * 获取applicationContext对象 * @return */
        public static ApplicationContext getApplicationContext(){
            return applicationContext;
        }
    
        /** * 根据bean的id来查找对象 * @param id * @return */
        public static Object getBeanById(String id){
            return applicationContext.getBean(id);
        }
    
        /** * 根据bean的class来查找对象 * @param c * @return */
        public static Object getBeanByClass(Class c){
            return applicationContext.getBean(c);
        }
    
        /** * 根据bean的class来查找所有的对象(包括子类) * @param c * @return */
        public static Map getBeansByClass(Class c){
            return applicationContext.getBeansOfType(c);
        }
    }

注：此时已经实现了class加载和bean的注册

**bean的调用**

Object aaa = (applicationContext.getBean(aClass.getName()));
            Method m = null;
            try {
                m = aClass.getMethod("getString", null);
            } catch (NoSuchMethodException e) {
                e.printStackTrace();
            }
            Object ret = null;
            try {
                ret = m.invoke(aaa, null);
            } catch (IllegalAccessException e) {
                e.printStackTrace();
            } catch (InvocationTargetException e) {
                e.printStackTrace();
            }
            return ret.toString();

注：此处的主要知识点是反射。

这样就实现了我们所要的功能。不重启服务，又能增加业务逻辑，是不是很牛。

[原码下载地址][Link 1]

[Link 1]: https://download.csdn.net/download/zhou8622/10290015