当我尝试使用mathUtil实例时，我得到空指针异常，因为它没有被注入。我认为因为创造是成功而不是注射？
下面是我的班级得到错误：
package com.cts.mms.process.service
@Component
public class MocalMathVerifier implements MathVerifer {
private static final Logger log = LoggerFactory.getLogger(MocalMathVerifier .class);
@Autowired
MathUtil mathUtil;
@Autowired
mathLogger mathLogger;
public verifyMaths(){
List<MathObject> mathObjList = mathUtil.getctList(mathList);
}
}
MY context.xml如下
<beans default-autowire="no"
xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context-2.5.xsd">
<context:property-placeholder location="classpath*:mmsogenmerfier.properties" />
<context:annotation-config />
<context:component-scan base-package="com.cts.mms.process"></context:component-scan>
<bean id="log4jInitialization"
class="org.springframework.beans.factory.config.MethodInvokingFactoryBean">
<property name="targetClass" value="org.springframework.util.Log4jConfigurer" />
<property name="targetMethod" value="initLogging" />
<property name="arguments">
<list>
<value>classpath:log4j.properties</value>
</list>
</property>
</bean>
<bean id="jaxb2Marshaller" class="org.springframework.oxm.jaxb.Jaxb2Marshaller">
<property name="classesToBeBound">
<array>
<value>com.cts.mms.process.oxm.metagen</value>
</array>
</property>
</bean>
<bean id="mailSender" class="org.springframework.mail.javamail.JavaMailSenderImpl">
<property name="host" value="localhost" />
<property name="port" value="25" />
<property name="username" value="" />
<property name="password" value="" />
<property name="javaMailProperties">
<props>
<prop key="mail.transport.protocol">smtp</prop>
<!-- <prop key="mail.smtp.auth">true</prop> -->
<!-- <prop key="mail.smtp.starttls.enable">true</prop> <prop key="mail.smtp.startssl.enable">true</prop> -->
<!-- <prop key="mail.debug">true</prop> -->
</props>
</property>
</bean>
<bean id="simpleMailMessage" class="org.springframework.mail.SimpleMailMessage">
<property name="from" value="${smtp.email.from}" />
<property name="to" value="${smtp.email.to}" />
<property name="subject" value="${smtp.email.subject}" />
<!-- <property name="text" value ="${stmp.email.bodyText}"/> -->
<property name="text">
<value>
<![CDATA[
Dear %s,
Mail Content : %s
]]>
</value>
</property>
</bean>
</beans>
下面是MathUtil类定义。从帖子中删除了认为没有必要的内容。
package com.cts.mms.process.common;
@Component("mathUtil")
public class MathUtil {
public List<MathObject> getctList(List<Maths> mathList) {
}
以下是如何访问MocalMathVerifier
package com.cts.mms.process.service;
@Component
public class MathVerifierFactory {
public MathVerifer getMathVerifier(Short mathtypeId){
if(mathtypeId==100 )
return new MocalMathVerifier();
}
}
package com.cts.mms.process.service;
@Component("verifier")
public class Verifier {
private static final Logger log = LoggerFactory.getLogger(Verifier.class);
@Autowired
private MathVerifierFactory mathVerifierFactory;
public void verifyMathInfo() {
mathVerifierFactory.getMathVerifier(mathId).verifyPaths(mathList);
}
答案 0 :(得分：0)
问题在于此代码：
if(mathtypeId==100 )
return new MocalMathVerifier();
}
只有在使用Spring IoC本身创建对象时，Spring IoC才能使用Autowire将依赖注入对象。如果您只是使用
创建对象new MocalMathVerifier();
Spring没有办法发现是时候在新创建的对象中注入依赖项了。
您可以通过以下方式更改课程：
@Component("verifier")
public class Verifier {
private static final Logger log = LoggerFactory.getLogger(Verifier.class);
@Autowired
private MocalMathVerifier mathVerifier;
public void verifyMathInfo() {
mathVerifier.verifyPaths(mathList);
}
如您所见，现在您要求Spring创建依赖项（mathVerifier）。当Spring创建（注入）它时，它也会注入它的依赖项（mathUtil，mathLogger）。
如果工厂包含选择/创建MathVerifier实例的逻辑，那么您仍有很多选项。您可以在Verifier类和MathVerifierFactory中自动装配工厂自动装配所有可能的MathVerifiers实例。它将类似于：
class MathVerifierFactory {
@Autowired
MocalMathVerifier mocalMathVerifier;
@Autowired
SomeOtherMathVerifier someOtherMathVerifier;
public MathVerifer getMathVerifier(Short mathtypeId){
if(mathtypeId==100 )
return mocalMathVerifier;
} else {
return someOtherMathVerifier;
}
}
}
但请注意，在这种情况下，您最终可能会在不同的clints之间共享MathVerifier的相同实例，这可能会产生共享状态和并发性问题。
另一种选择是将MathUtil和MathLogger注入工厂并手动创建MathVerifier实例：
class MathVerifierFactory {
@Autowired
MathUtil mathUtil;
@Autowired
MathLogger mathLogger;
public MathVerifer getMathVerifier(Short mathtypeId){
if(mathtypeId==100 )
return new MocalMathVerifier(mathUtil, mathLogger);
} else {
return new SomeOtherMathVerifier(mathLogger);
}
}
}
最后一种方法的问题是MathVerifier的不同子类可能具有不同的依赖关系，您可能需要MathVerifierFactory中的所有子类，这可能不是一个好的设计决策。您可以做的是为MathVerifier的每个子类型创建一个单独的工厂类。它将是这样的：
class MocalMathVerifierFactory {
@Autowired
MathUtils mathUtils;
@Autowired
MathLogger mathLogger;
MocalMathVerifier createMathVerifier() {
return new MocalMathVerifier(mathUtils, mathLogger);
}
}
class SomeOtherMathVeriferFactory {
@Autowired
MathLogger mathLogger;
MocalMathVerifier createMathVerifier() {
return new MocalMathVerifier(mathLogger);
}
}
class MathVerifierFactory {
@Autowired
MocalMathVerifierFactory mocalMathVerifierFactory;
@Autowired
SomeOtherMathVerifierFactory someOtherMathVerifierFactory;
public MathVerifer getMathVerifier(Short mathtypeId){
if(mathtypeId==100 )
return mocalMathVerifierFactory.createMathVerifier();
} else {
return someOtherMathVerifier.createMathVerifier();
}
}
}