Spring註冊bean的三種方式

時間 2019-12-29

原文原文鏈接

1）無參構造器註冊bean

實體類java

public class User {
    private String username;
    private String password;

    public User() {
        System.out.println("User類的無參構造方法User()執行了");
    }

    public String getUsername() {
        return username;
    }

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

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }
}

配置文件spring

<?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.xsd">

    <bean id="user" class="entity.User"></bean>

</beans>

測試類app

public class TestSpring {
    public static void main(String[] args) {
        ApplicationContext applicationContext = new ClassPathXmlApplicationContext("applicationContext.xml");
        User user = applicationContext.getBean("user", User.class);
        System.out.println(user);
    }
}

輸出結果測試

User類的無參構造方法User()執行了
entity.User@29774679

2）靜態工廠方法註冊bean

實體類this

public class User {
    private String username;
    private String password;

    public User() {
        System.out.println("User類的無參構造方法User()執行了");
    }

    public String getUsername() {
        return username;
    }

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

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }
}

工廠類code

public class UserFactory {
    private static User user;

    static {
        user = new User();
    }

    public static User getInstance() {
        return user;
    }
}

配置文件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"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
       http://www.springframework.org/schema/beans/spring-beans.xsd">

    <!-- factory-method：用於指定一個靜態工廠方法，Spring容器會調用這個靜態方法建立個對象。-->
    <bean id\="user" class\="entity.UserFactory" factory-method\="getInstance"\></bean>

</beans>

測試類對象

public class TestSpring {
    public static void main(String[] args) {
        ApplicationContext applicationContext = new ClassPathXmlApplicationContext("applicationContext.xml");
        User user = applicationContext.getBean("user", User.class);
        System.out.println(user);
    }
}

輸出結果get

User類的無參構造方法User()執行了
entity.User@5622fdf

3）實例工廠方法註冊bean

實體類it

java.util.Calendar  
    public final Date getTime()

配置文件

<?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.xsd">

    <!-- 靜態工廠方法註冊bean -->
    <bean id="calendar" class="java.util.Calendar" factory-method="getInstance"></bean>

    <!-- 
        實例工廠方法註冊bean：
            factory-bean：用於指定一個bean的id
            factory-method：用於指定一個方法
    -->
    <bean id="time" factory-bean="calendar" factory-method="getTime"></bean>

</beans>

測試類

@Test
public void test03() {
    ApplicationContext ac = new ClassPathXmlApplicationContext("applicationContext.xml");
    Date time = ac.getBean("time",Date.class);
    System.out.println(time);
}

測試結果