Spring + MyBaits 日志初始化两遍的问题
偶然发现一个问题,记录一下以备查询。
问题:系统启动时发现日志初始化了两次
14:28:04.798 [main] DEBUG org.apache.ibatis.logging.LogFactory - Logging initialized using 'class org.apache.ibatis.logging.slf4j.Slf4jImpl' adapter. 14:28:04.970 [main] DEBUG org.apache.ibatis.logging.LogFactory - Logging initialized using 'class org.apache.ibatis.logging.slf4j.Slf4jImpl' adapter.
相关环境文件
- mybatis-config.xml片段:
<settings>
<setting name="logImpl" value="SLF4J" /> <!-- 日志实现包 -->
</settings>
- applicitionContext.xml片段:
<!-- 配置SqlSessionFactoryBean -->
<bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
<property name="dataSource" ref="driverManagerDataSource" />
<property name="configLocation" value="classpath:mybatis-config.xml" />
</bean>
既然是LogFactory打印的日志,先从LogFactory开始看,
public final class LogFactory {
private static Constructor<? extends Log> logConstructor;
static { // 加载时按顺序尝试日志实现,这是第一条日志的输出
tryImplementation(new Runnable() {
public void run() {
useSlf4jLogging();
}
});
tryImplementation(new Runnable() {
public void run() {
useCommonsLogging();
}
}); // 忽略部分代码
tryImplementation(new Runnable() {
public void run() {
useNoLogging();
}
});
}
private LogFactory() { // disable construction
}
public static Log getLog(Class<?> aClass) {
return getLog(aClass.getName());
}
public static Log getLog(String logger) {
try {
return logConstructor.newInstance(new Object[] { logger });
} catch (Throwable t) {
throw new LogException("Error creating logger for logger " + logger + ". Cause: " + t, t);
}
}
public static synchronized void useCustomLogging(Class<? extends Log> clazz) { setImplementation(clazz); }
public static synchronized void useSlf4jLogging() { setImplementation(org.apache.ibatis.logging.slf4j.Slf4jImpl.class); }
public static synchronized void useCommonsLogging() { setImplementation(org.apache.ibatis.logging.commons.JakartaCommonsLoggingImpl.class); }
public static synchronized void useStdOutLogging() { setImplementation(org.apache.ibatis.logging.stdout.StdOutImpl.class); }
public static synchronized void useNoLogging() { setImplementation(org.apache.ibatis.logging.nologging.NoLoggingImpl.class); }
private static void tryImplementation(Runnable runnable) {
if (logConstructor == null) { // 当加载日志实现成功一次后,这里logConstructor已经不为null
try {
runnable.run();
} catch (Throwable t) { // ignore
}
}
}
private static void setImplementation(Class<? extends Log> implClass) {
try {
Constructor<? extends Log> candidate = implClass.getConstructor(new Class[] { String.class });
Log log = candidate.newInstance(new Object[] { LogFactory.class.getName() });
log.debug("Logging initialized using '" + implClass + "' adapter.");
logConstructor = candidate;
} catch (Throwable t) {
throw new LogException("Error setting Log implementation. Cause: " + t, t);
}
}
}
可以看出在spring容器启动时,已经加载了一个org.apache.ibatis.logging.slf4j.Slf4jImpl
;
那么第二条日志是什么时候输出呢?
容器在构造SqlSessionFactoryBean时,需要mybatis-config.xml,因为有<setting name="logImpl" value="SLF4J" />
这一条配置,
所以在解析到这一条时调用了org.apache.ibatis.session.Configuration
这个类又执行了一次初始化,
顺序 SqlSessionFactoryBean -> SqlSessionFactoryBuilder -> XMLConfigBuilder -> Configuration
最终 Configuration 中:
public void setLogImpl(Class<?> logImpl) {
if (logImpl != null) {
this.logImpl = (Class<? extends Log>) logImpl;
LogFactory.useCustomLogging(this.logImpl);
}
}
由此也看明白了配置日志实现相当于手动执行org.apache.ibatis.logging.LogFactory.useSlf4jLogging(),mybatis文档中也写到了:
如果要手动调用LogFactory.use***Logging()方法,请在调用所有其他MyBatis方法前调用它。另外,只有在相应日志实现存在 的前提下,调用对应的方法才是有意义的,否则MyBatis一概忽略。如你环境中并不存在Log4J,你却调用了 相应的方法,MyBatis就会忽略这一调用,代之默认的查找顺序查找日志实现。