Mybatis拦截器原理及实例

拦截器类型

1.Executor (update, query, flushStatements, commit, rollback, getTransaction, close, isClosed) 拦截执行器的方法
2.ParameterHandler (getParameterObject, setParameters) 拦截参数的处理
2.ResultSetHandler (handleResultSets, handleOutputParameters) 拦截结果集的处理
4.StatementHandler (prepare, parameterize, batch, update, query) 拦截Sql语法和会话构建的处理
执行顺序：Executor => StatementHandler => ParameterHandler => ResultSetHandler

拦截器应用场景

StatementHandler可改写sql 实现分页查询
ParameterHandler可改写拦截参数的处理，新增创建时间、创建人、更新时间等
ResultSetHandler数据库结果二次加密返回客户端，过滤掉审计字段、敏感字段

拦截器增加分页功能样例

@Intercepts({@Signature(type = StatementHandler.class, method = "prepare",
                        args = {Connection.class, Integer.class}),
            })
@Component
@Slf4j
public class SqlInterceptor implements Interceptor {
    @Value("${jarye.pagehelper.rule}")
    private String pagehelperRule;
    
    @Override
    public Object intercept(Invocation invocation) throws Throwable {
        StatementHandler statementHandler = (StatementHandler) invocation.getTarget();
        MetaObject metaObject = SystemMetaObject.forObject(statementHandler);
        MappedStatement mappedStatement = (MappedStatement) metaObject.getValue("delegate.mappedStatement");
        //sql类型
        SqlCommandType sqlCommandType = mappedStatement.getSqlCommandType();
        switch (sqlCommandType) {
                // 判断sql语句是为查询类型
            case SELECT:
                extendLimit(statementHandler);
                break;
        }
        
        
        return invocation.proceed();
    }
    
    @Override
    public Object plugin(Object target) {
        return Plugin.wrap(target, this);
    }
    
    
    @Override
    public void setProperties(Properties properties) {
        
    }
    
    /**
    * 对sql实现 修改  加上limit
    */
    private void extendLimit(StatementHandler statementHandler) throws NoSuchFieldException, IllegalAccessException {
        // 获取到原生sql语句
        BoundSql boundSql = statementHandler.getBoundSql();
        Class<? extends BoundSql> aClass = boundSql.getClass();
        // 使用反射机制修改原生sqk语句
        Field sql = aClass.getDeclaredField("sql");
        sql.setAccessible(true);
        String oldSqlStr = boundSql.getSql();
        // 后面加上 limit
        sql.set(boundSql, oldSqlStr + "   " + pagehelperRule);
    }
}

拦截器修改参数样例

@Intercepts({
        @Signature(type = ParameterHandler.class, method = "setParameters", args = PreparedStatement.class)
})
@Slf4j
@Component
public class ParamInterceptor implements Interceptor {


    private static final ObjectFactory DEFAULT_OBJECT_FACTORY = new DefaultObjectFactory();
    private static final ObjectWrapperFactory DEFAULT_OBJECT_WRAPPER_FACTORY = new DefaultObjectWrapperFactory();
    private static final ReflectorFactory REFLECTOR_FACTORY = new DefaultReflectorFactory();

    @Override
    public Object intercept(Invocation invocation) throws Throwable {
        // 获取拦截器拦截的设置参数对象DefaultParameterHandler
        ParameterHandler parameterHandler = (ParameterHandler) invocation.getTarget();

        // 通过mybatis的反射来获取对应的值
        MetaObject metaResultSetHandler = MetaObject.forObject(parameterHandler, DEFAULT_OBJECT_FACTORY, DEFAULT_OBJECT_WRAPPER_FACTORY, REFLECTOR_FACTORY);
        MappedStatement mappedStatement = (MappedStatement) metaResultSetHandler.getValue("mappedStatement");
        // 如果方法是无惨的，则parameterObject会存在空的情况
        Object parameterObject = metaResultSetHandler.getValue("parameterObject");
        //sql类型
        SqlCommandType sqlCommandType = mappedStatement.getSqlCommandType();
        // 回写parameterObject对象
        metaResultSetHandler.setValue("parameterObject", updateInsertParam(sqlCommandType, parameterObject));
        return invocation.proceed();
    }

    @Override
    public Object plugin(Object target) {
        return Plugin.wrap(target, this);
    }

    @Override
    public void setProperties(Properties properties) {

    }

    private Object updateInsertParam(SqlCommandType sqlCommandType, Object parameterObject) throws NoSuchFieldException, IllegalAccessException {
        if(null==parameterObject){
            return parameterObject;
        }
        Class<?> aClass = parameterObject.getClass();
        switch (sqlCommandType) {
            case INSERT:
                // 使用反射获取到createDatetime修改时间为当前系统时间
                Field createDatetime = aClass.getSuperclass().getDeclaredField("createDatetime");
                createDatetime.setAccessible(true);
                createDatetime.set(parameterObject, new Date());
            case UPDATE:
                //updateDatetime字段 修改时间为当前系统时间
                Field updateDatetime = aClass.getSuperclass().getDeclaredField("updateDatetime");
                updateDatetime.setAccessible(true);
                updateDatetime.set(parameterObject, new Date());
                break;
        }
        return parameterObject;
    }
}

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