Spring使用构造函数自动装配
这种模式是非常相似byType,但它应用于构造器参数。 Spring容器在外观上autowire属性被设置XML配置文件中bean的。然后,它尝试匹配和连线它的构造函数的参数与bean名称的配置文件只有一个。如果找到匹配项,它会注入这些bean,否则,它会抛出异常。
例如,如果一个bean定义设置为通过构造配置文件自动装配,它具有与拼写检查类型的参数之一的构造函数,春天寻找一个bean定义namedSpellChecker,并用它来设置构造函数的参数。仍然可以使用<constructor-arg>标签连线剩余的参数。下面的例子将说明这个概念。
让我们使用Eclipse IDE,然后按照下面的步骤来创建一个Spring应用程序:
步骤 | 描述 |
---|---|
1 | Create a project with a name SpringExample and create a package com.manongjc under the src folder in the created project. |
2 | Add required Spring libraries using Add External JARs option as explained in the Spring Hello World Example chapter. |
3 | Create Java classes TextEditor, SpellChecker and MainApp under the com.manongjcpackage. |
4 | Create Beans configuration file Beans.xml under the src folder. |
5 | The final step is to create the content of all the Java files and Bean Configuration file and run the application as explained below. |
这里是TextEditor.java文件的内容:
package com.manongjc;
public class TextEditor {
private SpellChecker spellChecker;
private String name;
public TextEditor( SpellChecker spellChecker, String name ) {
this.spellChecker = spellChecker;
this.name = name;
}
public SpellChecker getSpellChecker() {
return spellChecker;
}
public String getName() {
return name;
}
public void spellCheck() {
spellChecker.checkSpelling();
}
}
下面是另外一个相关的类文件SpellChecker.java内容:
package com.manongjc;
public class SpellChecker {
public SpellChecker(){
System.out.println("Inside SpellChecker constructor." );
}
public void checkSpelling()
{
System.out.println("Inside checkSpelling." );
}
}
以下是MainApp.java文件的内容:
package com.manongjc;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class MainApp {
public static void main(String[] args) {
ApplicationContext context =
new ClassPathXmlApplicationContext("Beans.xml");
TextEditor te = (TextEditor) context.getBean("textEditor");
te.spellCheck();
}
}
以下是在正常情况下的配置文件beans.xml文件:
<?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-3.0.xsd">
<!-- Definition for textEditor bean -->
<bean id="textEditor" class="com.manongjc.TextEditor">
<constructor-arg ref="spellChecker" />
<constructor-arg value="Generic Text Editor"/>
</bean>
<!-- Definition for spellChecker bean -->
<bean id="spellChecker" class="com.manongjc.SpellChecker">
</bean>
</beans>
但是,如果要使用由“构造函数”自动装配,那么XML配置文件将如下:
<?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-3.0.xsd">
<!-- Definition for textEditor bean -->
<bean id="textEditor" class="com.manongjc.TextEditor"
autowire="constructor">
<constructor-arg value="Generic Text Editor"/>
</bean>
<!-- Definition for spellChecker bean -->
<bean id="SpellChecker" class="com.manongjc.SpellChecker">
</bean>
</beans>
创建源代码和bean配置文件完成后,让我们运行应用程序。如果一切顺利,这将打印以下信息:
Inside SpellChecker constructor.
Inside checkSpelling.