前言
上一篇文章咱们聊了一下聊聊如何实现一个反对键值对的SPI。本期咱们来聊聊如何实现一个带有拦截器性能的SPI
什么是拦截器
指在某个办法或字段被拜访之前进行拦挡，而后在之前或之后退出某些操作
什么是拦截器链
指将拦截器按肯定的程序联结成一条链。在拜访被拦挡的办法或字段时，拦截器链中的拦截器就会按其之前定义的程序被调用
实现拦截器逻辑
本文实现思路外围：利用责任链+动静代理
1、定义拦截器接口
public interface Interceptor { int HIGHEST_PRECEDENCE = Integer.MIN_VALUE; int LOWEST_PRECEDENCE = Integer.MAX_VALUE; Object intercept(Invocation invocation) throws Throwable; default Object plugin(Object target) { return Plugin.wrap(target, this); } int getOrder();}2、自定义须要被拦截器拦挡的类接口注解
@Documented@Retention(RetentionPolicy.RUNTIME)@Target(ElementType.TYPE)public @interface Intercepts { Signature[] value();}@Documented@Retention(RetentionPolicy.RUNTIME)@Target({})public @interface Signature { Class<?> type(); String method(); Class<?>[] args();}3、通过jdk动静代理实现拦截器调用逻辑
public class Plugin implements InvocationHandler { private final Object target; private final Interceptor interceptor; private final Map<Class<?>, Set<Method>> signatureMap; private Plugin(Object target, Interceptor interceptor, Map<Class<?>, Set<Method>> signatureMap) { this.target = target; this.interceptor = interceptor; this.signatureMap = signatureMap; } public static Object wrap(Object target, Interceptor interceptor) { Map<Class<?>, Set<Method>> signatureMap = getSignatureMap(interceptor); Class<?> type = target.getClass(); Class<?>[] interfaces = getAllInterfaces(type, signatureMap); if (interfaces.length > 0) { return Proxy.newProxyInstance( type.getClassLoader(), interfaces, new Plugin(target, interceptor, signatureMap)); } return target; } @Override public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { try { Set<Method> methods = signatureMap.get(method.getDeclaringClass()); if (methods != null && methods.contains(method)) { Invocation invocation = new Invocation(target, method, args); return interceptor.intercept(invocation); } return method.invoke(target, args); } catch (Exception e) { throw ExceptionUtils.unwrapThrowable(e); } } private static Map<Class<?>, Set<Method>> getSignatureMap(Interceptor interceptor) { Intercepts interceptsAnnotation = interceptor.getClass().getAnnotation(Intercepts.class); if (interceptsAnnotation == null) { throw new PluginException("No @Intercepts annotation was found in interceptor " + interceptor.getClass().getName()); } Signature[] sigs = interceptsAnnotation.value(); Map<Class<?>, Set<Method>> signatureMap = new HashMap<>(); for (Signature sig : sigs) { Set<Method> methods = signatureMap.computeIfAbsent(sig.type(), k -> new HashSet<>()); try { Method method = sig.type().getMethod(sig.method(), sig.args()); methods.add(method); } catch (NoSuchMethodException e) { throw new PluginException("Could not find method on " + sig.type() + " named " + sig.method() + ". Cause: " + e, e); } } return signatureMap; } private static Class<?>[] getAllInterfaces(Class<?> type, Map<Class<?>, Set<Method>> signatureMap) { Set<Class<?>> interfaces = new HashSet<>(); while (type != null) { for (Class<?> c : type.getInterfaces()) { if (signatureMap.containsKey(c)) { interfaces.add(c); } } type = type.getSuperclass(); } return interfaces.toArray(new Class<?>[interfaces.size()]); }}4、结构出拦截器链
public class InterceptorChain { private final List<Interceptor> interceptors = new ArrayList<>(); public Object pluginAll(Object target) { if(CollectionUtil.isNotEmpty(interceptors)){ for (Interceptor interceptor : getInterceptors()) { target = interceptor.plugin(target); } } return target; } public InterceptorChain addInterceptor(Interceptor interceptor) { interceptors.add(interceptor); return this; } public List<Interceptor> getInterceptors() { List<Interceptor> interceptorsByOrder = interceptors.stream().sorted(Comparator.comparing(Interceptor::getOrder).reversed()).collect(Collectors.toList()); return Collections.unmodifiableList(interceptorsByOrder); }}5、通过拦截器链与之前实现的SPI绑定
@Activate@Slf4jpublic class InterceptorExtensionFactory implements ExtensionFactory { private InterceptorChain chain; @Override public <T> T getExtension(final String key, final Class<T> clazz) { if(Objects.isNull(chain)){ log.warn("No InterceptorChain Is Config" ); return null; } if (clazz.isInterface() && clazz.isAnnotationPresent(SPI.class)) { ExtensionLoader<T> extensionLoader = ExtensionLoader.getExtensionLoader(clazz); if (!extensionLoader.getSupportedExtensions().isEmpty()) { if(StringUtils.isBlank(key)){ return (T) chain.pluginAll(extensionLoader.getDefaultActivate()); } return (T) chain.pluginAll(extensionLoader.getActivate(key)); } } return null; } public InterceptorChain getChain() { return chain; } public InterceptorExtensionFactory setChain(InterceptorChain chain) { this.chain = chain; return this; }示例演示
1、定义拦截器并指明要拦挡的类接口办法
@Intercepts(@Signature(type = SqlDialect.class,method = "dialect",args = {}))public class MysqlDialectInterceptor implements Interceptor { @Override public Object intercept(Invocation invocation) throws Throwable { System.out.println("MysqlDialectInterceptor"); return invocation.proceed(); } @Override public int getOrder() { return HIGHEST_PRECEDENCE; } @Override public Object plugin(Object target) { if(target.toString().startsWith(MysqlDialect.class.getName())){ return Plugin.wrap(target,this); } return target; }}2、结构拦截器链并设置到spi工厂中
@Before public void before(){ InterceptorChain chain = new InterceptorChain(); chain.addInterceptor(new DialectInterceptor()).addInterceptor(new MysqlDialectInterceptor()).addInterceptor(new OracleDialectInterceptor()); factory = (InterceptorExtensionFactory) (ExtensionLoader.getExtensionLoader(ExtensionFactory.class).getActivate("interceptor")); factory.setChain(chain); }3、测试
@Test public void testMysqlDialectInterceptor(){ SqlDialect dialect = factory.getExtension("mysql",SqlDialect.class); Assert.assertEquals("mysql",dialect.dialect()); }
从控制台输入就能够看出曾经把拦截器调用逻辑实现进去
总结
看了本篇的拦截器实现，眼尖的敌人就会发现，你这不就是抄mybatis拦截器的实现。的确是这样，但我更违心不要脸的称这个为学以致用。mybatis的拦截器实现的确挺奇妙的，因为咱们惯例实现拦截器链调用失常是应用相似递归的形式，mybatis却借助了动静代理。
当然本篇的拦截器也加了一点彩蛋，比方减少了原生mybatis拦截器没提供的自定义执行程序性能，原生的mybatis拦截器只能拦挡Executor、ParameterHandler 、StatementHandler 、ResultSetHandler。而本文则没这个限度，但有个留神点是因为拦截器实现是基于jdk动静代理，因而自定义注解的class只能指定为接口，而不能是具体实现
demo链接
https://github.com/lyb-geek/springboot-learning/tree/master/springboot-spi-enhance/springboot-spi-framework