Spring框架总结（四）

对象依赖关系

Spring中，如何给对象的属性赋值?  【DI, 依赖注入】

         1) 通过构造函数

         2) 通过set方法给属性注入值

         3) p名称空间

         4)自动装配(了解)

         5) 注解

一、对象属性赋值，通过构造函数

user

public class User {

    private String userId;
    private String username;

    public User() {
        System.out.println("======不带参构造器=========");
    }

    public User(String userId, String username) {
        System.out.println("======带参构造器=========");
        this.userId = userId;
        this.username = username;
    }

    public String getUserId() {
        return userId;
    }

    public void setUserId(String userId) {
        this.userId = userId;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    @Override
    public String toString() {
        return "User [userId=" + userId + ", username=" + username + "]";
    }

}

bean.xml

<?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:p="http://www.springframework.org/schema/p"
    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">


    <!-- 对象属性赋值 通过构造函数 -->
    <bean id="user" class="com.liuyang.demo.property.User">
        <constructor-arg index="0" value="100"></constructor-arg>
        <constructor-arg index="1" value="小白兔"></constructor-arg>
    </bean>
</beans>

测试

public class App {

    ApplicationContext aContext = new ClassPathXmlApplicationContext(
            "com/liuyang/demo/property/beans2.xml");

    @Test
    public void test() {
        User user = (User) aContext.getBean("user1");

        System.out.println(user);
    }
}

二、通过set方法给属性注入值

更改bean，其他不变

<?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:p="http://www.springframework.org/schema/p"
    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">
<!-- set方法赋值 -->
    <bean id="user1" class="com.liuyang.demo.property.User">
        <property name="userId" value="101"></property>
        <property name="username" value="大虎猫"></property>
    </bean>

</beans>

事例一个set方法传值案例：

创建userdao

public class UserDAO {

    public void saveUser() {
        System.out
                .println("保存成功**********************************************");

    }

}

创建servicedao

public class UserService {
    private UserDAO dao;

    public void setDao(UserDAO dao) {
        this.dao = dao;
    }

    public void save() {
        dao.saveUser();
    }

}

创建action

public class UserAction {

    private UserService us;

    public void setUs(UserService us) {
        this.us = us;
    }

    public String execute() {
        us.save();
        return null;
    }

}

bean.xml

<?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:p="http://www.springframework.org/schema/p"
    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">


    <!-- 对象属性赋值 通过构造函数 -->
    <bean id="user" class="com.liuyang.test.DI.User">
    </bean>
    <!-- dao注入 -->
    <bean id="dao" class="com.liuyang.test.DI.UserDAO">
    </bean>

    <!-- service注入 -->
    <bean id="us" class="com.liuyang.test.DI.UserService">
        <property name="dao" ref="dao"></property>
    </bean>

    <!-- action注入 -->
    <bean id="userAction" class="com.liuyang.test.DI.UserAction">
        <property name="us" ref="us"></property>
    </bean>

测试

public class App {

    ApplicationContext aContext = new ClassPathXmlApplicationContext(
            "com/liuyang/test/DI/beans2.xml");

    @Test
    public void test() {
        UserAction userAction = (UserAction) aContext.getBean("userAction");

        userAction.execute();
    }
}

还有内部的bean写法如图,适用于只有一个dao和一个service的情况

<?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:p="http://www.springframework.org/schema/p"
    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">
<!-- 内部调用 dao和service在容器中只用一次,缺点不易维护-->
    <bean id="userAction1" class="com.liuyang.test.DI.UserAction">
        <property name="us">
            <bean class="com.liuyang.test.DI.UserService">
                <property name="dao">
                    <bean class="com.liuyang.test.DI.UserDAO"></bean>
                </property>
            </bean>
        </property>
    </bean>
</beans>

三、p名称空间的使用

(1)p引用的使用

保证约束条件有xmlns:p="http://www.springframework.org/schema/p"

更改bean.xml

<!-- 
            给对象属性注入值：
            # p 名称空间给对象的属性注入值
             (spring3.0以上版本才支持)
-->
<?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:p="http://www.springframework.org/schema/p"
    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">
<bean id="user" class="com.liuyang.test.DI.User">
    </bean>
    <bean id="dao" class="com.liuyang.test.DI.UserDAO"></bean>
    <bean id="us" class="com.liuyang.test.DI.UserService" p:dao-ref="dao"></bean>
    <bean id="userAction" class="com.liuyang.test.DI.UserAction"
        p:us-ref="us"></bean>
</beans>

(2)p传值的引用

<?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:p="http://www.springframework.org/schema/p"
    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">
<bean id="meinv" class="com.liuyang.test.DI.User" p:username="小白兔"></bean>
</beans>

p命名空间是一种优化