MyBatis源码分析(2)—— Plugin原理

@(MyBatis)[Plugin]

MyBatis源码分析——Plugin原理

Plugin原理

Plugin的兑现利用了Java的动态代理,应用了责任链设计格局

InterceptorChain

截留器链,用于保存从布局文件分析后的享有拦截器

插件链的创导

在Configuration解析配置文件的时候,XMLConfigBuilder.parseConfiguration中会调用pluginElement剖析插件音信并实例化后,保存到插件链中

// /configuration/plugins节点
private void pluginElement(XNode parent) throws Exception {
    if (parent != null) {
      // 获取所有的插件定义
      for (XNode child : parent.getChildren()) {
        String interceptor = child.getStringAttribute("interceptor");
        Properties properties = child.getChildrenAsProperties();
        // 反射,实例化插件
        Interceptor interceptorInstance = (Interceptor) resolveClass(interceptor).newInstance();
        interceptorInstance.setProperties(properties);
        // 保存到插件链中
        configuration.addInterceptor(interceptorInstance);
      }
    }
  }
// Configuration.addInterceptor
public void addInterceptor(Interceptor interceptor) {
    interceptorChain.addInterceptor(interceptor);
}

public class InterceptorChain {
  // 所有拦截器实例
  private final List<Interceptor> interceptors = new ArrayList<Interceptor>();

  public Object pluginAll(Object target) {
    for (Interceptor interceptor : interceptors) {
      target = interceptor.plugin(target);
    }
    return target;
  }

  public void addInterceptor(Interceptor interceptor) {
    interceptors.add(interceptor);
  }

  public List<Interceptor> getInterceptors() {
    return Collections.unmodifiableList(interceptors);
  }

}

MyBatis,插件拦截

在MyBatis中,只可以拦截四种接口的兑现类:

  • Executor
  • ParameterHandler
  • ResultSetHandler
  • StatementHandler
    每连串型的拦截形式都是一样的,这里取executor为例:
    在开创SqlSession的时候,会需要创造Executor实现类,在创立时,会调用插件链的加载插件效用:executor = (Executor) interceptorChain.pluginAll(executor);,该方法会形成一个调用链。

      // 依次调用每个插件的plugin方法,如果该插件无需拦截target,则直接返回target
      public Object pluginAll(Object target) {
        for (Interceptor interceptor : interceptors) {
          target = interceptor.plugin(target);
        }
        return target;
      }
    

    ##### Plugin

    插件代理的贯彻,这里运用了Java Dynamic Proxy

    public class Plugin implements InvocationHandler {
        // 需要被代理的实例
        private Object target;
        // 拦截器实例
        private Interceptor interceptor;
        // 拦截器需要拦截的方法摘要,这里Class键为Executor等上述的四个
        // 值为需要被拦截的方法
        private Map<Class<?>, Set<Method>> signatureMap;
    
        // 此类不能直接创建,需要通过静态方法wrap来创建代理类
        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();
            // 获取需要被代理类的所有待拦截的接口
            Class<?>[] interfaces = getAllInterfaces(type, signatureMap);
            if (interfaces.length > 0) {
                // 创建代理类
                return Proxy.newProxyInstance(type.getClassLoader(), interfaces,
                        new Plugin(target, interceptor, signatureMap));
            }
            // 没有需要拦截的方法,直接返回原实例
            return target;
        }
    
        // 在代理类中调用
        public Object invoke(Object proxy, Method method, Object[] args)
                throws Throwable {
            try {
                Set<Method> methods = signatureMap.get(method.getDeclaringClass());
                // 判断是否为待拦截方法,这里为动态判断,所有在拦截器多的时候,会影响性能
                if (methods != null && methods.contains(method)) {
                    return interceptor.intercept(new Invocation(target, method,
                            args));
                }
                return method.invoke(target, args);
            } catch (Exception e) {
                throw ExceptionUtil.unwrapThrowable(e);
            }
        }
        // 获取需要被拦截的方法摘要
        private static Map<Class<?>, Set<Method>> getSignatureMap(
                Interceptor interceptor) {
            // 先获取拦截器实现类上的注解,提取需要被拦截的方法
            /* 注解示例:@Intercepts(value={@Signature(args={Void.class},method="query",type=Void.class)})*/
            Intercepts interceptsAnnotation = interceptor.getClass().getAnnotation(
                    Intercepts.class);
            if (interceptsAnnotation == null) { // issue #251
                throw new PluginException(
                        "No @Intercepts annotation was found in interceptor "
                                + interceptor.getClass().getName());
            }
            Signature[] sigs = interceptsAnnotation.value();
            Map<Class<?>, Set<Method>> signatureMap = new HashMap<Class<?>, Set<Method>>();
            for (Signature sig : sigs) {
                Set<Method> methods = signatureMap.get(sig.type());
                if (methods == null) {
                    methods = new HashSet<Method>();
                    signatureMap.put(sig.type(), methods);
                }
                try {
                // 根据方法名以及参数获取待拦截方法
                    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<Class<?>>();
            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()]);
        }
    }
    

示例:

插件配置

在mybatis.xml配置文件:

<plugins>
    <plugin interceptor="com.jabnih.analysis.mybatis.interceptor.InterceptorDemo1"/>
    <plugin interceptor="com.jabnih.analysis.mybatis.interceptor.InterceptorDemo2"/>
</plugins>

插件实现

@Intercepts(value={@Signature(args={MappedStatement.class,Object.class},method="update",type=Executor.class)})
public class InterceptorDemo1 implements Interceptor {
    private Logger logger = LoggerFactory.getLogger(InterceptorDemo1.class);
    @Override
    public Object intercept(Invocation invocation) throws Throwable {
        logger.debug(InterceptorDemo1.class.getName());
        return invocation.proceed();
    }
    @Override
    public Object plugin(Object target) {
        return Plugin.wrap(target, this);
    }
    @Override
    public void setProperties(Properties properties) {
    }
}


@Intercepts(value={@Signature(args={MappedStatement.class,Object.class},method="update",type=Executor.class)})
public class InterceptorDemo2 implements Interceptor {
    private Logger logger = LoggerFactory.getLogger(InterceptorDemo2.class);
    @Override
    public Object intercept(Invocation invocation) throws Throwable {
        logger.debug(InterceptorDemo2.class.getName());
        return invocation.proceed();
    }
    @Override
    public Object plugin(Object target) {
        return Plugin.wrap(target, this);
    }
    @Override
    public void setProperties(Properties properties) {
    }
}

main方法

public static void main(String args[]) throws Exception {

    String resource = "mybatis.xml";
    InputStream inputStream = Resources.getResourceAsStream(resource);
    SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);

    SqlSession session = sqlSessionFactory.openSession();

    ProductMapper productMapper = session.getMapper(ProductMapper.class);

    productMapper.updatePriceById("ANV01", BigDecimal.valueOf(6.99));
}

输出结果

2016-07-09 16:59:00 [DEBUG]-[Thread: main]-[com.jabnih.analysis.mybatis.interceptor.InterceptorDemo2.intercept()]: 
com.jabnih.analysis.mybatis.interceptor.InterceptorDemo2

2016-07-09 16:59:00 [DEBUG]-[Thread: main]-[com.jabnih.analysis.mybatis.interceptor.InterceptorDemo1.intercept()]: 
com.jabnih.analysis.mybatis.interceptor.InterceptorDemo1

示范的调用连串图

图表太大,可能需要另开一个页面单独看
MyBatis 1

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