mybatis自定義插件（攔截器）開發詳解

時間 2019-11-06

原文原文鏈接

mybatis插件（準確的說應該是around攔截器，由於接口名是interceptor，並且invocation.proceed要本身調用，配置中叫插件）功能很是強大，可讓咱們無侵入式的對SQL的執行進行干涉，從SQL語句重寫、參數注入、結果集返回等每一個主要環節，典型的包括權限控制檢查與注入、只讀庫映射、K/V翻譯、動態改寫SQL。sql

MyBatis默認支持對4大對象（Executor，StatementHandler，ParameterHandler，ResultSetHandler）上的方法執行攔截，具體支持的方法爲：apache

Executor (update, query, flushStatements, commit, rollback, getTransaction, close, isClosed)，主要用於sql重寫。
ParameterHandler (getParameterObject, setParameters)，用於參數處理。
ResultSetHandler (handleResultSets, handleOutputParameters)，用於結果集二次處理。
StatementHandler (prepare, parameterize, batch, update, query)，用於jdbc層的控制。

大多數狀況下僅在Executor作插件好比SQL重寫、結果集脫敏，ResultSetHandler和StatementHandler僅在高級場景中使用，並且某些場景中很是有價值。mybatis

四大對象的在sql執行過程當中的調用鏈以下：app

具體的方法定義能夠參見每一個類方法的簽名，這裏就不詳細展開了。這四個類被建立後不是直接返回，而是創執行了interceptorChain.pluginAll(parameterHandler)才返回。以下所示：ide

//Configuration 中
public ParameterHandler newParameterHandler(MappedStatement mappedStatement, Object parameterObject, BoundSql boundSql) {
    ParameterHandler parameterHandler = mappedStatement.getLang().createParameterHandler(mappedStatement, parameterObject, boundSql);
    parameterHandler = (ParameterHandler) interceptorChain.pluginAll(parameterHandler);
    return parameterHandler;
}

public ResultSetHandler newResultSetHandler(Executor executor, MappedStatement mappedStatement, RowBounds rowBounds, ParameterHandler parameterHandler,
                                            ResultHandler resultHandler, BoundSql boundSql) {
    ResultSetHandler resultSetHandler = new DefaultResultSetHandler(executor, mappedStatement, parameterHandler, resultHandler, boundSql, rowBounds);
    resultSetHandler = (ResultSetHandler) interceptorChain.pluginAll(resultSetHandler);
    return resultSetHandler;
}

public StatementHandler newStatementHandler(Executor executor, MappedStatement mappedStatement, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) {
    StatementHandler statementHandler = new RoutingStatementHandler(executor, mappedStatement, parameterObject, rowBounds, resultHandler, boundSql);
    statementHandler = (StatementHandler) interceptorChain.pluginAll(statementHandler);
    return statementHandler;
}

public Executor newExecutor(Transaction transaction) {
    return newExecutor(transaction, defaultExecutorType);
}

public Executor newExecutor(Transaction transaction, ExecutorType executorType) {
    executorType = executorType == null ? defaultExecutorType : executorType;
    executorType = executorType == null ? ExecutorType.SIMPLE : executorType;
    Executor executor;
    if (ExecutorType.BATCH == executorType) {
        executor = new BatchExecutor(this, transaction);
    } else if (ExecutorType.REUSE == executorType) {
        executor = new ReuseExecutor(this, transaction);
    } else {
        executor = new SimpleExecutor(this, transaction);
    }
    if (cacheEnabled) {
        executor = new CachingExecutor(executor);
    }
    executor = (Executor) interceptorChain.pluginAll(executor);
    return executor;
}

編寫Interceptor的實現類

Executor攔截器this

@Intercepts({
        // @Signature(type = Executor.class, method = /* org.apache.ibatis.executor.Executor中定義的方法,參數也要對應 */"update", args = { MappedStatement.class, Object.class}),
        @Signature(type = Executor.class, method = "query", args = { MappedStatement.class, Object.class,RowBounds.class, ResultHandler.class }) })
public class SelectPruningColumnPlugin implements Interceptor {
    public static final ThreadLocal<ColumnPruning> enablePruning = new ThreadLocal<ColumnPruning>(){
        @Override
        protected ColumnPruning initialValue()
        {
            return null;
        }
    };
    
    Logger logger = LoggerFactory.getLogger(SelectPruningColumnPlugin.class);
    
    static int MAPPED_STATEMENT_INDEX = 0;// 這是對應上面的args的序號
    static int PARAMETER_INDEX = 1;
    static int ROWBOUNDS_INDEX = 2;
    static int RESULT_HANDLER_INDEX = 3;
    @Override
    public Object intercept(Invocation invocation) throws Throwable {
        if (enablePruning.get() != null && enablePruning.get().isEnablePruning()) {
            Object[] queryArgs = invocation.getArgs();
            MappedStatement mappedStatement = (MappedStatement) queryArgs[MAPPED_STATEMENT_INDEX];
            Object parameter = queryArgs[PARAMETER_INDEX];
            BoundSql boundSql = mappedStatement.getBoundSql(parameter);
            String sql = boundSql.getSql();// 獲取到SQL ，進行調整
            String name = mappedStatement.getId();
            logger.debug("攔截的方法名是:" + name + ",sql是" + sql + ",參數是" + JsonUtils.toJson(parameter));
            String execSql = pruningColumn(enablePruning.get().getReserveColumns(), sql);
            logger.debug("修改後的sql是:" + execSql);

            // 從新new一個查詢語句對像
            BoundSql newBoundSql = new BoundSql(mappedStatement.getConfiguration(), execSql, boundSql.getParameterMappings(), boundSql.getParameterObject());
            // 把新的查詢放到statement裏
            MappedStatement newMs = copyFromMappedStatement(mappedStatement, new BoundSqlSqlSource(newBoundSql));
            for (ParameterMapping mapping : boundSql.getParameterMappings()) {
                String prop = mapping.getProperty();
                if (boundSql.hasAdditionalParameter(prop)) {
                    newBoundSql.setAdditionalParameter(prop, boundSql.getAdditionalParameter(prop));
                }
            }
            queryArgs[MAPPED_STATEMENT_INDEX] = newMs;
            // 由於涉及分頁查詢PageHelper插件，因此不能設置爲null，須要業務上下文執行完成後設置爲null
//            enablePruning.set(null);
        }
        Object result = invocation.proceed();
        return result;
    }
    @Override
    public Object plugin(Object target) {
        return Plugin.wrap(target, this);
    }
    @Override
    public void setProperties(Properties properties) {
    }

ResultSetHandler攔截器spa

@Intercepts({
        @Signature(type = ResultSetHandler.class, method = "handleResultSets", args = { Statement.class}) })
public class OptMapPlugin implements Interceptor {
    @Override
    public Object intercept(Invocation invocation) throws Throwable {
        Object target = invocation.getTarget();
        Statement stmt = (Statement) invocation.getArgs()[0];
        if (target instanceof DefaultResultSetHandler) {
            DefaultResultSetHandler resultSetHandler = (DefaultResultSetHandler) target;
            Class clz = resultSetHandler.getMappedStatement().getResultMaps().get(0).getType();
            if (clz == OptMap.class) {
                List<Object> resultList = new ArrayList<Object>();
                OptMap optMap = new OptMap();
                resultList.add(optMap);
                resultSet2OptMap(resultSetHandler.getConfiguration(),resultSetHandler,optMap,stmt.getResultSet());
                return resultList;
            }
            return invocation.proceed();
        }
        //若是沒有進行攔截處理，則執行默認邏輯
        return invocation.proceed();
    }

最後將插件配置到mybatis-config.xml中，以下：

<!-- mybatis-config.xml  註冊插件-->
<plugins><plugin interceptor="io.yidoo.mybatis.plugin.SelectPruningColumnPlugin"><property name="someProperty" value="100"/></plugin>
</plugins>