java - @Autowired注解有什么好处？

Question

在我的 spring 示例中，我使用以下 XML 配置文件声明了两个 bean。

EmployeeBean.java

package autowire;

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

public class EmployeeBean {
    private String fullName;  
    @Autowired
    private DepartmentBean departmentBean; 


    public String getFullName() {
        return fullName;
    }
    public void setFullName(String fullName) {
        this.fullName = fullName;
    }
    public DepartmentBean getDepartmentBean() {
        return departmentBean;
    }


}

DepartmentBean.java

package autowire;

public class DepartmentBean {
    private String name;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

}

spring-servlet.xml

<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:p="http://www.springframework.org/schema/p"
    xmlns:context="http://www.springframework.org/schema/context" xmlns:tx="http://www.springframework.org/schema/tx"
    xmlns:mvc="http://www.springframework.org/schema/mvc"
    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
    http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-3.2.xsd
    http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc-3.2.xsd">


    <context:annotation-config />

    <bean id="employee" class="autowire.EmployeeBean" autowire="byType">
      <property name="fullName" value="Charith"></property>
    </bean>

    <bean id="deptment" class="autowire.DepartmentBean">
      <property name="name" value="IT Department"></property>
    </bean>


</beans>

TestAutowire.java

package autowire;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class TestAutowire {

    public static void main(String[] args) {
        ApplicationContext context =
                new ClassPathXmlApplicationContext(new String[] {"spring-servlet.xml"});

      EmployeeBean employee = (EmployeeBean)context.getBean("employee");
      System.out.println(employee.getFullName());
      System.out.println(employee.getDepartmentBean().getName());

    }

}

上面的示例工作正常。之后我删除了“@Autowired”注释并将以下行添加到 EmployeeBean.java

public void setDepartmentBean(DepartmentBean departmentBean) {
    this.departmentBean = departmentBean;
}

现在这个示例在相同的输出下工作正常。我的问题是，使用“@Autowired”注释时的实际好处是什么？因为代码在没有注释的情况下工作正常，但也使用 setter 方法。请帮助我。

Answer 1

@AutoWired 很有用，因为它可以节省您编写“接线”代码的时间。您不必在代码中的某个位置调用 setDepartment 方法来初始化对象。 Spring 会为你做到这一点。

根据您的情况，请参阅下文如何仅使用注释来完成此操作。请注意使用 @Component 注解来指示 Spring 自动扫描组件。另请注意，现在不需要 XML 文件。

EmployeeBean.java

package autowire;

/* Imports go here ... */

@Component
public class EmployeeBean {
    private String fullName;

    @Autowired
    private DepartmentBean departmentBean; 

    public String getFullName() {
        return fullName;
    }

    public void setFullName(String fullName) {
        this.fullName = fullName;
    }

    public DepartmentBean getDepartmentBean() {
        return departmentBean;
    }   
}

DepartmentBean.java

package autowire;

/* Imports go here ... */

@Component
public class DepartmentBean {
    private String name;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

TestAutowire.java

package autowire;

/* Imports go here ... */

public class TestAutowire {    
    public static void main(String[] args) {
      ApplicationContext context = new AnnotationConfigApplicationContext();
      context.scan("autowire");
      context.refresh();

      EmployeeBean employee = (EmployeeBean)context.getBean("employee");
      System.out.println(employee.getFullName());
      System.out.println(employee.getDepartmentBean().getName());
    }
}

引用文献:

• Spring 3.2.x: Java Based container configuration