JAVA应用场景拦截器、过滤器、监听器

一、mybatis--拦截器--Interceptor

1、应用场景：对特定SQL语句-赋值权限操作。

例如：对于有自定义注解权限的查询。做限制

2、自定义MyDataInterceptor 实现Interceptor接口

3、添加@Intercepts注解。标识该类为拦截类。

4、自定义注解

5、代码

       原理：利用反射得到类和注解。给符合特定注解的方法。修改原SQL。构建新SQL

@Intercepts({@Signature(type = Executor.class, method = "query", args = {MappedStatement.class, Object.class, RowBounds.class, ResultHandler.class})})
public class MyDataInterceptor implements Interceptor {
 
 
    public Object intercept(Invocation invocation) throws Throwable {
        Object[] args = invocation.getArgs();
        MappedStatement statement = (MappedStatement) args[0];
 
        System.out.println("进入拦截");
 
        Method method = invocation.getMethod();
        System.out.println("方法为" + method.getName());
 
        String id = statement.getId();
        String substring = id.substring(0, id.lastIndexOf("."));
        String substring1 = id.substring(id.lastIndexOf(".") + 1);
 
        Class<?> aClass = Class.forName(substring);
        boolean flag = false;
        Method[] declaredMethods = aClass.getDeclaredMethods();
        String myAnnotation = null;
        for (Method declaredMethod : declaredMethods) {
            Annotation[] declaredAnnotations = declaredMethod.getDeclaredAnnotations();
 
            for (Annotation declaredAnnotation : declaredAnnotations) {
                System.out.println(declaredAnnotation.annotationType().getTypeName());
                //TODO 可以做到数据库配置。也可以写枚举类
                if ("com.mybatisplus.config.MyAnnotation".equals(declaredAnnotation.annotationType().getTypeName())) {
                    MyAnnotation annotation = declaredMethod.getAnnotation(MyAnnotation.class);
                    StatusEnum[] statusEnums = annotation.value();
                    for (StatusEnum statusEnum : statusEnums) {
                        System.out.println(statusEnum.getAce());
                    }
 
                    flag = true;
                }
                System.out.println("注解为" + declaredAnnotation.annotationType().getSimpleName());
                myAnnotation = declaredAnnotation.annotationType().getSimpleName();
            }
        }
 
        Annotation[] annotations = method.getDeclaredAnnotations();
 
        //MyAnnotation myAnnotation = method.getAnnotation(MyAnnotation.class);
 
 
        ParameterMap parameterMap = statement.getParameterMap();
 
        SqlSource sqlSource = statement.getSqlSource();
 
 
        BoundSql boundSql = statement.getBoundSql(args[1]);
        String sql = boundSql.getSql();
        if (flag) {
            sql = sql + " and 1=0";
        } else {
            return invocation.proceed();
        }
 
 
        BoundSql boundSqlnew = new BoundSql(statement.getConfiguration(), sql, boundSql.getParameterMappings(), boundSql.getParameterObject());
 
        BoundSqlSqlSource source = new BoundSqlSqlSource(boundSqlnew);
 
        MappedStatement statement1 = newMappedStatement(statement, source);
 
        Object[] queryArgs = invocation.getArgs();
        queryArgs[0] = statement1;
 
 
        Object target = invocation.getTarget();
        return invocation.proceed();
    }
 
 
    /**
     * 定义一个内部辅助类，作用是包装 SQL
     */
    static class BoundSqlSqlSource implements SqlSource {
 
        private final BoundSql boundSql;
 
        public BoundSqlSqlSource(BoundSql boundSql) {
            this.boundSql = boundSql;
        }
 
        @Override
        public BoundSql getBoundSql(Object parameterObject) {
            return boundSql;
        }
 
    }
 
 
    private static MappedStatement newMappedStatement(MappedStatement ms, SqlSource newSqlSource) {
 
 
        /**
         * Configuration configuration, String id, SqlSource sqlSource, SqlCommandType sqlCommandType
         */
        MappedStatement.Builder mst = new MappedStatement.Builder(ms.getConfiguration(), ms.getId(), newSqlSource, ms.getSqlCommandType());
 
        mst.resource(ms.getResource());
        mst.fetchSize(ms.getFetchSize());
        mst.statementType(ms.getStatementType());
        mst.keyGenerator(ms.getKeyGenerator());
        if (ms.getKeyProperties() != null && ms.getKeyProperties().length > 0) {
            mst.keyProperty(ms.getKeyProperties()[0]);
        }
        mst.timeout(ms.getTimeout());
        mst.parameterMap(ms.getParameterMap());
        mst.resultMaps(ms.getResultMaps());
        mst.resultSetType(ms.getResultSetType());
        mst.cache(ms.getCache());
        mst.flushCacheRequired(ms.isFlushCacheRequired());
        mst.useCache(ms.isUseCache());
 
        return mst.build();
    }
 
 
    //DbType.MYSQL
}

二、webMvc拦截器

1、应用场景登录拦截或者访问拦截。

2、自定义拦截类MyHandlerInterceptor实现HandlerInterceptor接口

3、自定义mvc配置类MyMvcConfig（添加@Configuration）实现WebMvcConfigurer接口。并实现

addInterceptors方法

4、代码：

      原理：还是对原生的HttpServletRequest，HttpServletResponse进行处理

@Component
public class MyHandlerInterceptor implements HandlerInterceptor {
 
    /**
     * 前置处理器
     * @param request
     * @param response
     * @param handler
     * @return
     * @throws Exception
     */
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        System.out.println("我是前置处理器");
        return true;
    }
 
    /**
     * 执行器
     * @param request
     * @param response
     * @param handler
     * @param modelAndView
     * @throws Exception
     */
    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
        System.out.println("我是业务后置处理器");
    }
 
    /**
     * 后置处理器
     * @param request
     * @param response
     * @param handler
     * @param ex
     * @throws Exception
     */
    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        System.out.println("我是后置处理器");
    }
}

@Configuration
public class MyMvcConfig implements WebMvcConfigurer {
 
    @Resource
    private MyHandlerInterceptor interceptor;
 
    /**
     * 添加自定义拦截器
     * @param registry
     */
    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        System.out.println("拦截所有");
        registry.addInterceptor(interceptor).addPathPatterns("/*");
    }
}

三、过滤器