Spring中的自动装配案例分析
Spring_Autowiring collaborators
在Spring3.2.2中自动装配类型，分别为：no(default)(不采用自动装配)、byName，byType，constructor下面来分别介绍一下这些是如何自动装配的
<bean id="foo" class="...Foo" autowire="autowire type">
| Mode |
Explanation |
| 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. |
| byName |
Autowiring by property name. Spring looks for a bean with the same name as the property that needs to be autowired. For example, if a bean definition is set to autowire by name, and it contains a master property (that is, it has a setMaster(..) method), Spring looks for a bean definition named master, and uses it to set the property. |
| 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. |
| 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. |
案例分析：
1、创建CumputerBean类
package www.csdn.spring.autowire.bean;
public class CumputerBean {
// 电脑名称
private String name;
public void setName(String name) {
this.name = name;
}
@Override
public String toString() {
return "CumputerBean [name=" + name + "]";
}
}
2、创建DeptBean 类
package www.csdn.spring.autowire.bean;
public class DeptBean {
//部门名称
private String name;
public void setName(String name) {
this.name = name;
}
@Override
public String toString() {
return "DeptBean [name=" + name + "]";
}
}
3、创建EmployeeBean
package www.csdn.spring.autowire.bean;
public class EmployeeBean {
private DeptBean deptBean;
private CumputerBean cumputerBean;
public void setDeptBean(DeptBean deptBean) {
this.deptBean = deptBean;
}
public void setCumputerBean(CumputerBean cumputerBean) {
this.cumputerBean = cumputerBean;
}
@Override
public String toString() {
return "EmployeeBean [deptBean=" + deptBean + ", cumputerBean="
+ cumputerBean + "]";
}
}
首先分析no、byName、byType的配置都是采用setter方法依赖注入实现的案例
1、no配置（通过ref=””引用需要的bean）
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd">
<!-- 电脑bean -->
<bean id="cumputerBean" class="www.csdn.spring.autowire.bean.CumputerBean">
<property name="name" value="HP6325笔记本" />
</bean>
<!-- 部门bean -->
<bean id="deptBean" class="www.csdn.spring.autowire.bean.DeptBean">
<property name="name" value="CSDN教育事业部" />
</bean>
<!-- 员工bean 根据EmployeeBean中的 属性名称 去匹配-->
<bean id="employeeBean" class="www.csdn.spring.autowire.bean.EmployeeBean">
<property name="cumputerBean" ref="cumputerBean" />
<property name="deptBean" ref="deptBean" />
</bean>
</beans>
2、byName配置(分析:会根据EmployeeBean中属性的名称 自动装配)
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd">
<!-- 电脑bean -->
<bean id="cumputerBean" class="www.csdn.spring.autowire.bean.CumputerBean">
<property name="name" value="HP6325笔记本" />
</bean>
<!-- 部门bean -->
<bean id="deptBean" class="www.csdn.spring.autowire.bean.DeptBean">
<property name="name" value="CSDN教育事业部" />
</bean>
<!-- 员工bean-->
<bean id="employeeBean" class="www.csdn.spring.autowire.bean.EmployeeBean" autowire="byName"/>
</beans>
3、byType配置(分析:会根据EmployeeBean中属性的类型 自动装配)
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd">
<!-- 电脑bean -->
<bean id="cumputerBean" class="www.csdn.spring.autowire.bean.CumputerBean">
<property name="name" value="HP6325笔记本" />
</bean>
<!-- 部门bean -->
<bean id="deptBean" class="www.csdn.spring.autowire.bean.DeptBean">
<property name="name" value="CSDN教育事业部" />
</bean>
<!-- 员工bean 根据EmployeeBean中的 属性名称 去匹配-->
<bean id="employeeBean" class="www.csdn.spring.autowire.bean.EmployeeBean" autowire="byType"/>
</beans>
注意：当根据byType类型装配时，当在容器内找到多个匹配的类型时会出现如下bug
org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'employeeBean' defined in class path resource [spring-byType.xml]: Unsatisfied dependency expressed through bean property 'deptBean': : No qualifying bean of type [www.csdn.spring.autowire.bean.DeptBean] is defined: expected single matching bean but found 2: deptBean,deptBean1; nested exception is org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type [www.csdn.spring.autowire.bean.DeptBean] is defined: expected single matching bean but found 2: deptBean,deptBean1
4、Constructor(构造器参数根据byType类型匹配，自动装配)
首先修改EmployeeBean类 修改后代码如下：
package www.csdn.spring.autowire.bean;
public class EmployeeBean {
private DeptBean deptBean;
private CumputerBean cumputerBean;
public EmployeeBean(DeptBean deptBean, CumputerBean cumputerBean) {
super();
this.deptBean = deptBean;
this.cumputerBean = cumputerBean;
}
@Override
public String toString() {
return "EmployeeBean [deptBean=" + deptBean + ", cumputerBean="
+ cumputerBean + "]";
}
}
配置文件操作：
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd">
<!-- 电脑bean -->
<bean id="cumputerBean" class="www.csdn.spring.autowire.bean.CumputerBean">
<property name="name" value="HP6325笔记本" />
</bean>
<!-- 部门bean -->
<bean id="deptBean" class="www.csdn.spring.autowire.bean.DeptBean">
<property name="name" value="CSDN教育事业部" />
</bean>
<!-- 员工bean 根据EmployeeBean中的 属性名称 bytype 去匹配 -->
<bean id="employeeBean" class="www.csdn.spring.autowire.bean.EmployeeBean"
autowire="constructor">
</bean>
</beans>
说明:
1、当构造器的参数类型在容器中找不全时。
比如：
配置文件中只配置了CumpterBean时
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd">
<!-- 电脑bean -->
<bean id="cumputerBean" class="www.csdn.spring.autowire.bean.CumputerBean">
<property name="name" value="HP6325笔记本" />
</bean>
<!-- 员工bean 根据EmployeeBean中的 属性名称 bytype 去匹配 -->
<bean id="employeeBean" class="www.csdn.spring.autowire.bean.EmployeeBean"
autowire="constructor">
</bean>
</beans>
会出现如下bug:
org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'employeeBean' defined in class path resource [spring-constructors.xml]: Unsatisfied dependency expressed through constructor argument with index 0 of type [www.csdn.spring.autowire.bean.DeptBean]: : No qualifying bean of type [www.csdn.spring.autowire.bean.DeptBean] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {}; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type [www.csdn.spring.autowire.bean.DeptBean] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {}
Caused by:
org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type [www.csdn.spring.autowire.bean.DeptBean] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {}
2、当配置文件找到构造器参数的类型有多个的时候比如配置文件如下：
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd">
<!-- 电脑bean -->
<bean id="cumputerBean" class="www.csdn.spring.autowire.bean.CumputerBean">
<property name="name" value="HP6325笔记本" />
</bean>
<!-- 部门bean -->
<bean id="deptBean" class="www.csdn.spring.autowire.bean.DeptBean">
<property name="name" value="CSDN教育事业部" />
</bean>
<!-- 部门bean -->
<bean id="deptBean1" class="www.csdn.spring.autowire.bean.DeptBean">
<property name="name" value="CSDN教育事业部" />
</bean>
<!-- 员工bean 根据EmployeeBean中的 属性名称 bytype 去匹配 -->
<bean id="employeeBean" class="www.csdn.spring.autowire.bean.EmployeeBean"
autowire="constructor">
</bean>
</beans>
说明：上面配置有两个同样类型的DeptBean但是不会出现bug，原因是在EmployeeBean中构造器接受的参数名称与deptBean一致。
3、当配置文件找到构造器参数的类型有多个的时候比如配置文件如下：
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd">
<!-- 电脑bean -->
<bean id="cumputerBean" class="www.csdn.spring.autowire.bean.CumputerBean">
<property name="name" value="HP6325笔记本" />
</bean>
<!-- 部门bean -->
<bean id="deptBean1" class="www.csdn.spring.autowire.bean.DeptBean">
<property name="name" value="CSDN教育事业部" />
</bean>
<!-- 部门bean -->
<bean id="deptBean2" class="www.csdn.spring.autowire.bean.DeptBean">
<property name="name" value="CSDN教育事业部" />
</bean>
<!-- 员工bean 根据EmployeeBean中的 属性名称 bytype 去匹配 -->
<bean id="employeeBean" class="www.csdn.spring.autowire.bean.EmployeeBean"
autowire="constructor">
</bean>
</beans>
会出现如下bug（与byType的bug一致）:
org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'employeeBean' defined in class path resource [spring-constructors.xml]: Unsatisfied dependency expressed through constructor argument with index 0 of type [www.csdn.spring.autowire.bean.DeptBean]: : No qualifying bean of type [www.csdn.spring.autowire.bean.DeptBean] is defined: expected single matching bean but found 2: deptBean1,deptBean2; nested exception is org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type [www.csdn.spring.autowire.bean.DeptBean] is defined: expected single matching bean but found 2: deptBean1,deptBean2