由Spring Quartz 实例化时抛出SQL Exception的问题来看spring的autowire（自动装配）

项目使用Spring Quartz，声明如下schedule：

<beans default-autowire="byName">
	...
	<bean id="schedulerBackend" class="org.springframework.scheduling.quartz.SchedulerFactoryBean">
	   	<property name="schedulerName">
			<value>quartz_backend</value>
		</property>
	    <property name="triggers">
			<list>
				<!-- 自定义Cron trigger bean -->
				<ref local="Customer_CronTriggerBean"/>
	      </list>
	    </property>
	</bean>
</beans>

OAS环境下部署应用抛出如下异常：

[ERROR][2010-03-02 15:06:25,549] Context initialization failed
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'backEndService' defined in class path resource [service-appContext.xml]: Cannot resolve reference to bean 'schedulerBackend' while setting bean property 'scheduler'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'schedulerBackend' defined in class path resource [service-appContext.xml]: Invocation of init method failed; nested exception is org.quartz.SchedulerConfigException: Failure occured during job recovery. [See nested exception: org.quartz.impl.jdbcjobstore.LockException: Failure obtaining db row lock: ORA-00942: table or view does not exist
 [See nested exception: java.sql.SQLException: ORA-00942: table or view does not exist
]]
	at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveReference(BeanDefinitionValueResolver.java:275)
	at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveValueIfNecessary(BeanDefinitionValueResolver.java:104)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyPropertyValues(AbstractAutowireCapableBeanFactory.java:1210)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:978)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:462)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory$1.run(AbstractAutowireCapableBeanFactory.java:404)
	at java.security.AccessController.doPrivileged(Native Method)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:375)
... ...
Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'schedulerBackend' defined in class path resource [service-appContext.xml]: Invocation of init method failed; nested exception is org.quartz.SchedulerConfigException: Failure occured during job recovery. [See nested exception: org.quartz.impl.jdbcjobstore.LockException: Failure obtaining db row lock: ORA-00942: table or view does not exist
 [See nested exception: java.sql.SQLException: ORA-00942: table or view does not exist
]]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1302)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:463)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory$1.run(AbstractAutowireCapableBeanFactory.java:404)
	at java.security.AccessController.doPrivileged(Native Method)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:375)
	... 35 more
Caused by: org.quartz.SchedulerConfigException: Failure occured during job recovery. [See nested exception: org.quartz.impl.jdbcjobstore.LockException: Failure obtaining db row lock: ORA-00942: table or view does not exist
 [See nested exception: java.sql.SQLException: ORA-00942: table or view does not exist
]]
	at org.quartz.impl.jdbcjobstore.JobStoreSupport.initialize(JobStoreSupport.java:493)
	at org.quartz.impl.jdbcjobstore.JobStoreCMT.initialize(JobStoreCMT.java:144)
	... 45 more

本身定义的Quartz部分的应用根本涉及不到DB， 怎么会抛出SQL Exception呢，
查看一下出问题的源码

org.springframework.scheduling.quartz.SchedulerFactoryBean

 if(dataSource != null)mergedProps.put("org.quartz.jobStore.class", (org.springframework.scheduling.quartz.LocalDataSourceJobStore.class).getName());

看来异常就抛出在这个地方，但是SchedulerFactoryBean的dataSource属性并没有指定啊，为什么不为空呢？
上网搜了一下，原来问题出在Spring配置文件的autowire上。
spring提供了一个通过配置文件进行注入的很简便的功能，就是<beans default-autowire="byName">这段，翻了一下Spring的官方文档，autowire可以配置5个值：

no -- (Default) No autowiring. Bean references must be defined via a ref element. Changing the default setting is not recommended for larger deployments, because specifying collaborators explicitly gives greater control and clarity. To some extent, it documents the structure of a system.
默认值，不自动装配，给Bean注入属性必须通过<ref />标签，基于较大的spring配置文件，推荐使用这个默认值而不是其他的值，对每一个bean的注入都单独指定，这样比较清晰切易读，一个bean被注入了哪些属性，每个属性都注入的是什么值 都明确指定，一定程度上体现了一个系统的层次结构。

byName -- Autowiring by property name. Spring looks for a bean with the same name as the property that needs to be autowired.
按照属性的名称装配，spring根据bean的属性名自动在指定范围内搜索，如果找到名称匹配的的bean描述，就自动注入给定义的bean。而之前启动quartz失败，也正是因为spring的配置文件指定了default-autowire="byName"，而项目中其他部分用的datasource正好命名成通用的“dataSource”，这样spring就“自作聪明”把项目里用的dataSource也注入给了本不想要它的SchedulerFactoryBean。

byType -- Allows a property to be autowired if exactly one bean of the property type exists in the container. If more than one exists, a fatal exception is thrown, which indicates that you may not use byType autowiring for that bean. If there are no matching beans, nothing happens; the property is not set. If this is not desirable, setting the dependency-check="objects" attribute value specifies that an error should be thrown in this case.
按照类型装配，按照文档的描述，还是不用它为妙，举例：一个bean1有一个属性是A类型的，而上下文中有一个bean2是A类型的，这样spring就自动把bean2的实例赋值给bean1的这个属性。当上下文中有多个A类型的bean时，这个配置会导致抛出致命异常，而那个A类型的属性也不会set值。

constructor -- Analogous to byType, but applies to constructor arguments. If there is not exactly one bean of the constructor argument type in the container, a fatal error is raised.
byType的一个变通，只是把byType情况的属性替换为构造函数的参数。相当于上例中的这个bean1的属性改成bean1的构造方法的一个参数。spring把相同类型的bean赋值给这个参数。同类型的参数多于一个时也会抛出致命异常

autodetect -- Chooses constructor or byType through introspection of the bean class. If a default constructor is found, the byType mode is applied.
自动指定，按照类型和按照构造器的一个折衷，如果bean1有默认构造器（无参），则按照byType处理，否则，按照constructor处理。

理解了上面的描述，再回头来看这个问题，解决方案就明朗了：
方法一：去掉default-autowire="byName"配置，也就是用默认配置，这样spring就不会隐式的注入值给属性
方法二：如果想保留byName配置，可以显式的注入null给bean，这样spring也不会把不期望的值再注入给属性，比如上面的配置文件可以改成如下

<beans default-autowire="byName">
	...
	<bean id="schedulerBackend" class="org.springframework.scheduling.quartz.SchedulerFactoryBean">
		<property name="dataSource">
			<null /><!-- null 标签，强制把dataSource属性设置为空-->
		</property>
	   	<property name="schedulerName">
			<value>quartz_backend</value>
		</property>
	    <property name="triggers">
			<list>
				<!-- 自定义Cron trigger bean -->
				<ref local="Customer_CronTriggerBean"/>
	      </list>
	    </property>
	</bean>
</beans>
这里要注意，如果设置成<value><null/></value>,是不对的，<null />标签直接配置给<property>标签。

方法三： 使byName的配置对这个bean失效，这就有好多实现方式了，例如官方文档上说
Avoid autowiring for a bean definition by setting its autowire-candidate attributes to false ..
也就是把这个bean的autowire-candidate设置为false

<beans default-autowire="byName">
	...
	<bean id="schedulerBackend" autowire-candidate="false" class="org.springframework.scheduling.quartz.SchedulerFactoryBean">
	   	<property name="schedulerName">
			<value>quartz_backend</value>
		</property>
	    <property name="triggers">
			<list>
				<!-- 自定义Cron trigger bean -->
				<ref local="Customer_CronTriggerBean"/>
	      </list>
	    </property>
	</bean>
</beans>