Spring学习（三）—— 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