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springboot2教程系列

MyBatis提供了一種外掛(plugin)的功能，雖然叫做外掛，但其實這是攔截器功能

MyBatis 允許攔截的介面

MyBatis 允許你在已對映語句執行過程中的某一點進行攔截呼叫。預設情況下，MyBatis 允許使用外掛來攔截的方法呼叫包括：

1. Executor (update, query, flushStatements, commit, rollback, getTransaction, close, isClosed)
2. ParameterHandler (getParameterObject, setParameters)
3. ResultSetHandler (handleResultSets, handleOutputParameters)
4. StatementHandler (prepare, parameterize, batch, update, query)

Executor介面的部分方法，比如update，query，commit，rollback等方法，還有其他介面的一些方法等。

總體概括為：

1. 攔截執行器的方法
2. 攔截引數的處理
3. 攔截結果集的處理,為sql執行之後的結果攔截過濾
4. 攔截Sql語法構建的處理,為sql執行之前的攔截進行sql封裝

MyBatis攔截器的介面定義

一共有三個方法intercept 、plugin 、setProperties

setProperties()

方法主要是用來從配置中獲取屬性。

如果是使用xml式配置攔截器，可在Mybatis配置檔案中新增如下節點，屬性可以以如下方式傳遞

<plugins>
	<plugin interceptor="tk.mybatis.simple.plugin.XXXInterceptor">
		<property name="propl" value="valuel" />
		<property name="prop2" value="value2" />
	</plugin>
</plugins>
 

如果在Spring boot中使用，則需要單獨寫一個配置類，如下：

@Configuration
public class MybatisInterceptorConfig {
    @Bean
    public String myInterceptor(SqlSessionFactory sqlSessionFactory) {
        ExecutorInterceptor executorInterceptor = new ExecutorInterceptor();
        Properties properties = new Properties();
        properties.setProperty("prop1","value1");
        executorInterceptor.setProperties(properties);
        return "interceptor";
    }
}

如果說不需要配置屬性，則在spring boot中，不需要去編寫配置類，只需要像我一樣在攔截器上加個@Component即可。

plugin()

方法用於指定哪些方法可以被此攔截器攔截。

intercept()

方法是用來對攔截的sql進行具體的操作。

註解實現

MyBatis攔截器用到了兩個註解：@Intercepts和@Signature

@Intercepts(
        {
                @Signature(type = Executor.class, method = "query",
                        args = {MappedStatement.class, Object.class,
                                RowBounds.class, ResultHandler.class}),
                @Signature(type = Executor.class, method = "query",
                        args = {MappedStatement.class, Object.class, RowBounds.class,
                                ResultHandler.class, CacheKey.class, BoundSql.class}),
        }
)

type的值與類名相同，method與方法名相同，為了避免方法過載，args中指定了各個引數的型別和個數，可通過invocation.getArgs()獲取引數陣列。

Executor 攔截器實現

@Intercepts({
        @Signature(
        type= Executor.class,
        method = "query",
        args = {MappedStatement.class, Object.class, RowBounds.class, ResultHandler.class}
        )
})
@Slf4j
@Component
public class ExecutorInterceptor implements Interceptor {
    @Override
    public Object intercept(Invocation invocation) throws Throwable {
        String sql = ExecutorPluginUtils.getSqlByInvocation(invocation);
        //可以對sql重寫
        log.error("攔截器ExecutorInterceptor:"+sql);
        //sql = "SELECT id from BUS_RECEIVER where id = ? ";
        ExecutorPluginUtils.resetSql2Invocation( invocation,  sql);
        return invocation.proceed();
    }

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

    @Override
    public void setProperties(Properties properties) {

    }


}

ParameterHandler 攔截器實現

/**
 * @Author: ynz
 * @Date: 2018/12/23/023 12:07
 */
@Intercepts({
        @Signature(type = ParameterHandler.class, method = "setParameters", args = PreparedStatement.class),
})
@Component
@Slf4j
public class ParamInterceptor  implements Interceptor {

    @Override
    public Object intercept(Invocation invocation) throws Throwable {

        log.error("攔截器ParamInterceptor");
        //攔截 ParameterHandler 的 setParameters 方法 動態設定引數
        if (invocation.getTarget() instanceof ParameterHandler) {
            ParameterHandler parameterHandler = (ParameterHandler) invocation.getTarget();
            PreparedStatement ps = (PreparedStatement) invocation.getArgs()[0];

            // 反射獲取 BoundSql 物件，此物件包含生成的sql和sql的引數map對映
            Field boundSqlField = parameterHandler.getClass().getDeclaredField("boundSql");
            boundSqlField.setAccessible(true);
            BoundSql boundSql = (BoundSql) boundSqlField.get(parameterHandler);
            // 反射獲取 引數對像
            Field parameterField = 
                    parameterHandler.getClass().getDeclaredField("parameterObject");
            parameterField.setAccessible(true);
            Object parameterObject = parameterField.get(parameterHandler);

            if (parameterObject instanceof Map) {
                //將引數中的name值改為2
                ((Map) parameterObject).put("name","2");
            }

            // 改寫的引數設定到原parameterHandler物件
            parameterField.set(parameterHandler, parameterObject);
            parameterHandler.setParameters(ps);


            log.error(JSON.toJSONString(boundSql.getParameterMappings()));
            log.error(JSON.toJSONString(parameterObject));
        }
        return invocation.proceed();
    }

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

    @Override
    public void setProperties(Properties properties) {

    }
}

ResultSetHandler 攔截器實現

@Intercepts({
        @Signature(type = ResultSetHandler.class, method = "handleResultSets", args={Statement.class})
})
@Component
@Slf4j
public class ResultInterceptor implements Interceptor {

    @Override
    public Object intercept(Invocation invocation) throws Throwable {
        log.error("攔截器ResultInterceptor");
       // ResultSetHandler resultSetHandler1 = (ResultSetHandler) invocation.getTarget();
        //通過java反射獲得mappedStatement屬性值
        //可以獲得mybatis裡的resultype
        Object result = invocation.proceed();
        if (result instanceof ArrayList) {
            ArrayList resultList = (ArrayList) result;
            for (int i = 0; i < resultList.size(); i++) {
                Object oi = resultList.get(i);
                Class c = oi.getClass();
                Class[] types = {String.class};
                Method method = c.getMethod("setAddress", types);
                // 呼叫obj物件的 method 方法
                method.invoke(oi, "china");
            }
        }
        return result;
    }

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

    @Override
    public void setProperties(Properties properties) {

    }
}

StatementHandler 攔截器實現

/**
 * @Author: ynz
 * @Date: 2018/12/23/023 14:22
 */
@Intercepts(
        {@Signature(
                type = StatementHandler.class,
                method = "prepare",
                args = {Connection.class, Integer.class}
                )
        })
@Component
@Slf4j
public class StatementInterceptor implements Interceptor {

    @Override
    public Object intercept(Invocation invocation) throws Throwable {
        StatementHandler statementHandler = 
                (StatementHandler) PluginUtils.realTarget(invocation.getTarget());
        MetaObject metaStatementHandler = SystemMetaObject.forObject(statementHandler);
        MappedStatement mappedStatement = 
                (MappedStatement) metaStatementHandler.getValue("delegate.mappedStatement");
        //只攔截select方法
        if (!SqlCommandType.SELECT.equals(mappedStatement.getSqlCommandType())) {
            return invocation.proceed();
        }
        BoundSql boundSql = (BoundSql) metaStatementHandler.getValue("delegate.boundSql");
        //獲取到sql
        String originalSql = boundSql.getSql();
        //可以對originalSql進行改寫
        log.error("攔截器StatementInterceptor:"+originalSql);
        metaStatementHandler.setValue("delegate.boundSql.sql", originalSql);
        Object parameterObject = boundSql.getParameterObject();
        return invocation.proceed();
    }

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

    @Override
    public void setProperties(Properties properties) {

    }
}

Spring Boot整合

方法1：手寫一個配置類

@Configuration
public class MybatisInterceptorConfig {
    @Bean
    public String myInterceptor(SqlSessionFactory sqlSessionFactory) {
        ExecutorInterceptor executorInterceptor = new ExecutorInterceptor();
        Properties properties = new Properties();
        properties.setProperty("prop1","value1");
        executorInterceptor.setProperties(properties);
        sqlSessionFactory.getConfiguration().addInterceptor(executorInterceptor);
        sqlSessionFactory.getConfiguration().addInterceptor(new ParamInterceptor());
        sqlSessionFactory.getConfiguration().addInterceptor(new ResultInterceptor());
        return "interceptor";
    }
}

方法2：在攔截器上加@Component註解