要實現SQL執行時間統計，可以結合MyBatis和Log4j來實現。首先需要在MyBatis的配置文件中配置Log4j的日志輸出，示例如下：

<configuration>
    <settings>
        <setting name="logImpl" value="LOG4J"/>
    </settings>

    <properties>
        <property name="log4j.rootLogger" value="DEBUG, stdout"/>
        <property name="log4j.appender.stdout" value="org.apache.log4j.ConsoleAppender"/>
        <property name="log4j.appender.stdout.layout" value="org.apache.log4j.PatternLayout"/>
        <property name="log4j.appender.stdout.layout.ConversionPattern" value="%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n"/>
    </properties>
</configuration>

然后在Log4j的配置文件中配置輸出格式和日志級別，示例如下：

log4j.rootLogger=DEBUG, stdout

log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n

接著在MyBatis的Mapper接口中使用@Intercepts注解和@Signature注解來實現對SQL執行時間的攔截和統計，示例如下：

@Intercepts({
    @Signature(type = Executor.class, method = "update", args = {MappedStatement.class, Object.class}),
    @Signature(type = Executor.class, method = "query", args = {MappedStatement.class, Object.class, RowBounds.class, ResultHandler.class})
})
public class SqlStatsInterceptor implements Interceptor {

    @Override
    public Object intercept(Invocation invocation) throws Throwable {
        long startTime = System.currentTimeMillis();
        Object result = invocation.proceed();
        long endTime = System.currentTimeMillis();
        long time = endTime - startTime;

        MappedStatement mappedStatement = (MappedStatement) invocation.getArgs()[0];
        String sqlId = mappedStatement.getId();
        String sql = mappedStatement.getBoundSql(invocation.getArgs()[1]).getSql();

        Logger logger = LoggerFactory.getLogger(SqlStatsInterceptor.class);
        logger.info("Execute SQL [{}] cost {}ms", sqlId, time);

        return result;
    }

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

    @Override
    public void setProperties(Properties properties) {
    }
}

最后，在MyBatis的配置文件中注冊攔截器，示例如下：

<plugins>
    <plugin interceptor="com.example.interceptor.SqlStatsInterceptor"/>
</plugins>

通過以上步驟，就可以實現對SQL執行時間的統計并輸出到Log4j日志中。