Spring注解学习

最原始的Spring配置

public class Book {
    private String name;
    private double price;

    //...... name和price的get/set方法

    @Override
    public String toString() {
        return "Book [name=" + name + ", price=" + price + "]";
    }
}

public class Cls {

    private String classNo = "605";

     //...... classNo的get/set方法

    @Override
    public String toString() {
        return "Cls [classNo=" + classNo + "]";
    }
}

public class Student {

    private Book book;
    private Cls cls;

     //...... book和cls的get/set方法

    @Override
    public String toString() {
        return "Student [book=" + book + ", cls=" + cls + "]";
    }
}

<?xml version="1.0" encoding="GBK"?>
<beans xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns="http://www.springframework.org/schema/beans"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean id="boss" class="com.stu.Student">
        <property name="book" ref="book" />
        <property name="cls" ref="cls" />
    </bean>

    <bean id="book" class="com.stu.Book">
        <property name="name" value="Spring学习笔记" />
        <property name="price" value="199" />
    </bean>
    <bean id="cls" class="com.stu.Cls">
        <property name="classNo" value="807" />
    </bean>
</beans>

Test代码

public class AnnotationTest {
    public static void main(String[] args) {
        ApplicationContext ctx = new ClassPathXmlApplicationContext("beans.xml");
        Book book = ctx.getBean("book", Book.class);
        System.out.println(book);
    }
}

使用注解

@Autowired

首先需要在xml中配置bean

<bean class="org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor" />

然后在需要自动注入的变量上面添加注释@Autowired

public class Student {

    @Autowired
    private Book book;
    @Autowired
    private Cls cls;

    @Override
    public String toString() {
        return "Student [book=" + book + ", cls=" + cls + "]";
    }
}

还可以将@Autowired添加在set函数和构造函数上，效果等同.
在注入的时候没有发现Bean时会抛出NoSuchBeanDefinitionException，为了避免在没有找到Bean的时候不抛出异常，使用@Autowired(required = false)

简化beans.xml配置

使用<context:annotation-config/>替代<bean class="org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor" />

<?xml version="1.0" encoding="GBK"?>
<beans xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns="http://www.springframework.org/schema/beans"
    xmlns:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/context
    http://www.springframework.org/schema/beans/spring-beans.xsd
    http://www.springframework.org/schema/beans/spring-context.xsd">

    <context:annotation-config />

    <bean id="boss" class="com.stu.Student" />

    <bean id="book" class="com.stu.Book">
        <property name="name" value="Spring学习笔记" />
        <property name="price" value="199" />
    </bean>

    <bean id="cls" class="com.stu.Cls">
        <property name="classNo" value="807" />
    </bean>
</beans>

到目前为止，还是需要在beans.xml里面配置bean
@Component、@Service、@Constroller注解的使用
@Component：表示一个Bean
@Service：功能与Component一样，一般在业务层使用
@Constroller：功能与Component一样，一般在控制层使用

@Component

@Component
public class Book {
}
@Component
public class Cls {
}
// 可以指定bean名
@Component("student")
public class Student {
}

使用Component还需要修改beans.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns="http://www.springframework.org/schema/beans"
    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.xsd">

    <!-- 需要指定需要扫描的类包，寻找Component -->
    <context:component-scan base-package="com.stu" />
</beans>