mybatis自定义插件(拦截器)开发详解
mybatis插件(准确的说应该是around拦截器,因为接口名是interceptor,而且invocation.proceed要自己调用,配置中叫插件)功能非常强大,可以让我们无侵入式的对SQL的执行进行干涉,从SQL语句重写、参数注入、结果集返回等每个主要环节,典型的包括权限控制检查与注入、只读库映射、K/V翻译、动态改写SQL。
MyBatis默认支持对4大对象(Executor,StatementHandler,ParameterHandler,ResultSetHandler)上的方法执行拦截,具体支持的方法为:
- Executor (update, query, flushStatements, commit, rollback, getTransaction, close, isClosed),主要用于sql重写。
- ParameterHandler (getParameterObject, setParameters),用于参数处理。
- ResultSetHandler (handleResultSets, handleOutputParameters),用于结果集二次处理。
- StatementHandler (prepare, parameterize, batch, update, query),用于jdbc层的控制。
大多数情况下仅在Executor做插件比如SQL重写、结果集脱敏,ResultSetHandler和StatementHandler仅在高级场景中使用,而且某些场景中非常有价值。
四大对象的在sql执行过程中的调用链如下:
具体的方法定义可以参见每个类方法的签名,这里就不详细展开了。这四个类被创建后不是直接返回,而是创执行了interceptorChain.pluginAll(parameterHandler)才返回。如下所示:
//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; }
编写Interceptor的实现类
Executor拦截器
@Intercepts({ // @Signature(type = Executor.class, method = /* org.apache.ibatis.executor.Executor中定义的方法,参数也要对应 */"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;// 这是对应上面的args的序号 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();// 获取到SQL ,进行调整 String name = mappedStatement.getId(); logger.debug("拦截的方法名是:" + name + ",sql是" + sql + ",参数是" + JsonUtils.toJson(parameter)); String execSql = pruningColumn(enablePruning.get().getReserveColumns(), sql); logger.debug("修改后的sql是:" + execSql); // 重新new一个查询语句对像 BoundSql newBoundSql = new BoundSql(mappedStatement.getConfiguration(), execSql, boundSql.getParameterMappings(), boundSql.getParameterObject()); // 把新的查询放到statement里 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; // 因为涉及分页查询PageHelper插件,所以不能设置为null,需要业务上下文执行完成后设置为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拦截器
@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(); } //如果没有进行拦截处理,则执行默认逻辑 return invocation.proceed(); }
最后将插件配置到mybatis-config.xml中,如下:
<!-- mybatis-config.xml 注册插件--> <plugins> <plugin interceptor="io.yidoo.mybatis.plugin.SelectPruningColumnPlugin"> <property name="someProperty" value="100"/> </plugin> </plugins>