@Required 注释应用于 bean 属性的 setter 方法,它表明受影响的 bean 属性在配置时必须放在 XML 配置文件中,否则容器就会抛出一个BeanInitializationException 异常

下面显示的是一个使用 @Required 注释的示例。

  • 新建一个Spring项目

  • 创建 Java 类 Student 和 MainApp

下面是 Student.java 文件的内容:

package hello;
import org.springframework.beans.factory.annotation.Required; public class Student {
private int age;
String name;
@Required
public void setAge(int age){
this.age = age;
}
public int getAge(){
return age;
}
@Required
public void setName(String name){
this.name = name;
}
public String getName(){
return name;
}
}

下面是 MainApp.java 文件的内容:

package hello;
//import org.springframework.context.support.AbstractApplicationContext;
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");
Student student = (Student) context.getBean("student");
System.out.println("name: "+ student.getName());
System.out.println("age: "+ student.getAge());
}
}

下面是配置文件 Beans.xml: 文件的内容:

<?xml version="1.0" encoding="UTF-8"?>
<beans 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-3.0.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context-3.0.xsd"> <context:annotation-config/> <!-- Definition for student bean-->
<bean id="student" class="hello.Student" >
<property name="name" value="fanqie"/>
<property name="age" value="20"/>
</bean> </beans>

运行结果如下:

name: fanqie
age: 20

总结:

1、要在使用@Required 注释的java文件中引入:

import org.springframework.beans.factory.annotation.Required;

2、配置文件Beans.xml的前面要如下书写,否则会出错:

<?xml version="1.0" encoding="UTF-8"?>

<beans 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-3.0.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context-3.0.xsd"> <context:annotation-config/>
<!-- bean definitions go here --> </beans>

3、 bean 属性的 setter 方法在配置时必须放在 XML 配置文件中,否则会出错

 @Required
public void setAge(Integer age) {
this.age = age;
} @Required
public void setName(String name) {
this.name = name;
}

如上面有两个setter方法,则age和nama属性都必须放在XML配置文件中。

每天学习一点点,每天进步一点点。

05-29 00:54