Spring系列:基於XML的方式構建IOC

Code技術分享發表於2023-11-07

一、搭建模組spring6-ioc-xml

①引入配置檔案

引入spring6-ioc-xml模組配置檔案:beans.xml、log4j2.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">

    <bean id="user" class="com.mcode.bean.User"/>
</beans>

②新增依賴

<dependencies>
       <!--spring context依賴-->
       <!--當你引入Spring Context依賴之後,表示將Spring的基礎依賴引入了-->
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-context</artifactId>
            <version>6.0.13</version>
        </dependency>
       <!--junit5測試-->
        <dependency>
            <groupId>org.junit.jupiter</groupId>
            <artifactId>junit-jupiter-api</artifactId>
            <version>5.9.3</version>
        </dependency>
       <!--log4j2的依賴-->
        <dependency>
            <groupId>org.apache.logging.log4j</groupId>
            <artifactId>log4j-core</artifactId>
            <version>2.20.0</version>
        </dependency>
        <dependency>
            <groupId>org.apache.logging.log4j</groupId>
            <artifactId>log4j-slf4j2-impl</artifactId>
            <version>2.20.0</version>
        </dependency>
    </dependencies>

③引入java類

引入spring6-ioc-xml模組java及test目錄下實體類

package com.mcode.bean;

/**
 * ClassName: User
 * Package: com.mcode.bean
 * Description:
 *
 * @Author: robin
 * @Create: 2023/11/7 - 10:33 PM
 * @Version: v1.0
 */
public class User {
    public User() {
        System.out.println("無引數構造方法執行");
    }

    public void test(){
        System.out.println("test...");
    }
}
package com.mcode;

import com.mcode.bean.Student;
import com.mcode.bean.User;
import org.junit.jupiter.api.Test;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.context.support.ClassPathXmlApplicationContext;

/**
 * ClassName: UserTest
 * Package: com.mcode
 * Description:
 *
 * @Author: robin
 * @Create: 2023/11/7 - 10:34 PM
 * @Version: v1.0
 */
public class UserTest {
    private Logger logger = LoggerFactory.getLogger(UserTest.class);

    @Test
    public void testUser(){
    }
}

二、獲取bean的三種方式

①方式一:根據id獲取

由於 id 屬性指定了 bean 的唯一標識,所以根據 bean 標籤的 id 屬性可以精確獲取到一個元件物件。

    @Test
    public void testUser(){
        ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext("beans.xml");
        User user = (User) applicationContext.getBean("user");
        user.test();
    }

②方式二:根據型別獲取

    @Test
    public void testUser1(){
        ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext("beans.xml");
        User user = (User) applicationContext.getBean(User.class);
        user.test();
    }

③方式三:根據id和型別

    @Test
    public void testUser2(){
        ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext("beans.xml");
        User user = (User) applicationContext.getBean("user",User.class);
        user.test();
    }

④注意的地方

當根據型別獲取bean時,要求IOC容器中指定型別的bean有且只能有一個

當IOC容器中一共配置了兩個:

    <bean id="user" class="com.mcode.bean.User"/>
    <bean id="user2" class="com.mcode.bean.User"/>

根據型別獲取時會丟擲異常:

org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type 'com.mcode.bean.User' available: expected single matching bean but found 2: user,user2

三、基於setter注入

①建立學生類Student

package com.mcode.bean;

/**
 * ClassName: Student
 * Package: com.mcode.bean
 * Description:
 *
 * @Author: robin
 * @Create: 2023/11/7 - 10:46 PM
 * @Version: v1.0
 */
public class Student {
    private Integer id;
    private String  name;
    private Integer age;
    private String sex;

    public Student() {
    }

    @Override
    public String toString() {
        return "Student{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", age=" + age +
                ", sex='" + sex + '\'' +
                '}';
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

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

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }
}

②配置bean時為屬性賦值

spring-di.xml

<bean id="studentOne" class="com.mcode.bean.Student">
    <!-- property標籤:透過元件類的setXxx()方法給元件物件設定屬性 -->
    <!-- name屬性:指定屬性名(這個屬性名是getXxx()、setXxx()方法定義的,和成員變數無關) -->
    <!-- value屬性:指定屬性值 -->
     <property name="id" value="1"></property>
     <property name="name" value="robin"></property>
     <property name="age" value="18"></property>
     <property name="sex" value="男"></property>
</bean>

③測試

    @Test
    public void testDIBySet(){
        ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext("spring-di.xml");
        Student student = applicationContext.getBean("studentOne", Student.class);
        System.out.println(student);
    }

四、基於構造器注入

①在Student類中新增有參構造

public Student(Integer id, String name, Integer age, String sex) {
    this.id = id;
    this.name = name;
    this.age = age;
    this.sex = sex;
}

②配置bean

spring-di.xml

    <bean id="studentTwo" class="com.mcode.bean.Student">
        <constructor-arg value="1"></constructor-arg>
        <constructor-arg value="robin"></constructor-arg>
        <constructor-arg value="20"></constructor-arg>
        <constructor-arg value="男"></constructor-arg>
    </bean>

注意:

constructor-arg標籤還有兩個屬性可以進一步描述構造器引數:

  • index屬性:指定引數所在位置的索引(從0開始)
  • name屬性:指定引數名

③測試

    @Test
    public void testDIByConstructor(){
        ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext("spring-di.xml");
        Student student = applicationContext.getBean("studentTwo", Student.class);
        System.out.println(student);
    }

五、特殊值處理

①字面量賦值

什麼是字面量?

int a = 10;

宣告一個變數a,初始化為10,此時a就不代表字母a了,而是作為一個變數的名字。當我們引用a的時候,我們實際上拿到的值是10。

而如果a是帶引號的:'a',那麼它現在不是一個變數,它就是代表a這個字母本身,這就是字面量。所以字面量沒有引申含義,就是我們看到的這個資料本身。

<!-- 使用value屬性給bean的屬性賦值時,Spring會把value屬性的值看做字面量 -->
<property name="name" value="張三"/>

②null值

<property name="name">
    <null />
</property>

注意:

<property name="name" value="null"></property>

以上寫法,為name所賦的值是字串null

③xml實體

<!-- 小於號在XML文件中用來定義標籤的開始,不能隨便使用 -->
<!-- 解決方案一:使用XML實體來代替 -->
<property name="expression" value="a &lt; b"/>

④CDATA節

<property name="expression">
    <!-- 解決方案二:使用CDATA節 -->
    <!-- CDATA中的C代表Character,是文字、字元的含義,CDATA就表示純文字資料 -->
    <!-- XML解析器看到CDATA節就知道這裡是純文字,就不會當作XML標籤或屬性來解析 -->
    <!-- 所以CDATA節中寫什麼符號都隨意 -->
    <value><![CDATA[a < b]]></value>
</property>

六、為物件型別屬性賦值

①建立班級類Clazz

package com.mcode.bean;

/**
 * ClassName: Clazz
 * Package: com.mcode.bean
 * Description:
 *
 * @Author: robin
 * @Create: 2023/11/7 - 10:53 PM
 * @Version: v1.0
 */
public class Clazz {
    private Integer clazzId;
    private String clazzName;

    public Clazz() {
    }

    public Clazz(Integer clazzId, String clazzName) {
        this.clazzId = clazzId;
        this.clazzName = clazzName;
    }

    @Override
    public String toString() {
        return "Clazz{" +
                "clazzId=" + clazzId +
                ", clazzName='" + clazzName + '\'' +
                '}';
    }

    public Integer getClazzId() {
        return clazzId;
    }

    public void setClazzId(Integer clazzId) {
        this.clazzId = clazzId;
    }

    public String getClazzName() {
        return clazzName;
    }

    public void setClazzName(String clazzName) {
        this.clazzName = clazzName;
    }
}

②修改Student類

在Student類中新增以下程式碼:

private Clazz clazz;

public Clazz getClazz() {
	return clazz;
}

public void setClazz(Clazz clazz) {
	this.clazz = clazz;
}

方式一:引用外部bean

配置Clazz型別的bean:

<bean id="clazzOne" class="com.mcode.bean.Clazz">
    <property name="clazzId" value="1111"></property>
    <property name="clazzName" value="財源滾滾班"></property>
</bean>

為Student中的clazz屬性賦值:

<bean id="studentFour" class="com.mcode.bean.Student">
    <property name="id" value="1004"></property>
    <property name="name" value="趙六"></property>
    <property name="age" value="26"></property>
    <property name="sex" value="女"></property>
    <!-- ref屬性:引用IOC容器中某個bean的id,將所對應的bean為屬性賦值 -->
    <property name="clazz" ref="clazzOne"></property>
</bean>

方式二:內部bean

<bean id="studentFour" class="com.mcode.bean.Student">
    <property name="id" value="1004"></property>
    <property name="name" value="趙六"></property>
    <property name="age" value="26"></property>
    <property name="sex" value="女"></property>
    <property name="clazz">
        <!-- 在一個bean中再宣告一個bean就是內部bean -->
        <!-- 內部bean只能用於給屬性賦值,不能在外部透過IOC容器獲取,因此可以省略id屬性 -->
        <bean id="clazzInner" class="com.mcode.bean.Clazz">
            <property name="clazzId" value="2222"></property>
            <property name="clazzName" value="遠大前程班"></property>
        </bean>
    </property>
</bean>

方式三:級聯屬性賦值

<bean id="studentFour" class="com.mcode.bean.Student">
    <property name="id" value="1004"></property>
    <property name="name" value="趙六"></property>
    <property name="age" value="26"></property>
    <property name="sex" value="女"></property>
    <property name="clazz" ref="clazzOne"></property>
    <property name="clazz.clazzId" value="3333"></property>
    <property name="clazz.clazzName" value="最強王者班"></property>
</bean>

七、引入外部屬性檔案

①加入依賴

 <!-- MySQL驅動 -->
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>8.0.30</version>
</dependency>

<!-- 資料來源 -->
<dependency>
    <groupId>com.alibaba</groupId>
    <artifactId>druid</artifactId>
    <version>1.2.15</version>
</dependency>

②建立外部屬性檔案

jdbc.user=root
jdbc.password=123456
jdbc.url=jdbc:mysql://localhost:3306/ssm?serverTimezone=UTC
jdbc.driver=com.mysql.cj.jdbc.Driver

③引入屬性檔案

引入context 名稱空間

<?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.xsd
       http://www.springframework.org/schema/context
       http://www.springframework.org/schema/context/spring-context.xsd">

</beans>
<!-- 引入外部屬性檔案 -->
<context:property-placeholder location="classpath:jdbc.properties"/>

注意:在使用 context:property-placeholder 元素載入外包配置檔案功能前,首先需要在 XML 配置的一級標籤 中新增 context 相關的約束。

④配置bean

<bean id="druidDataSource" class="com.alibaba.druid.pool.DruidDataSource">
    <property name="url" value="${jdbc.url}"/>
    <property name="driverClassName" value="${jdbc.driver}"/>
    <property name="username" value="${jdbc.user}"/>
    <property name="password" value="${jdbc.password}"/>
</bean>

⑤測試

@Test
public void testDataSource() throws SQLException {
    ApplicationContext ac = new ClassPathXmlApplicationContext("spring-datasource.xml");
    DataSource dataSource = ac.getBean(DataSource.class);
    Connection connection = dataSource.getConnection();
    System.out.println(connection);
}

八、基於XML自動裝配

自動裝配:

根據指定的策略,在IOC容器中匹配某一個bean,自動為指定的bean中所依賴的類型別或介面型別屬性賦值

①場景模擬

建立類UserController

package com.mcode.autowire.controller;

import com.mcode.autowire.service.UserService;

/**
 * ClassName: UserController
 * Package: com.mcode.autowire.controller
 * Description:
 *
 * @Author: robin
 * @Create: 2023/11/7 - 11:29 PM
 * @Version: v1.0
 */
public class UserController {
    private UserService userService;


    public void setUserService(UserService userService) {
        this.userService = userService;
    }

    public void getUser(){
        userService.getUser();
    }

}

建立介面UserService

package com.mcode.autowire.service;

/**
 * ClassName: UserService
 * Package: com.mcode.autowite.service
 * Description:
 *
 * @Author: robin
 * @Create: 2023/11/7 - 11:30 PM
 * @Version: v1.0
 */
public interface UserService {
    void getUser();
}

建立類UserServiceImpl實現介面UserService

package com.mcode.autowire.service.impl;

import com.mcode.autowire.service.UserService;

/**
 * ClassName: UserServiceImpl
 * Package: com.mcode.autowire.service.impl
 * Description:
 *
 * @Author: robin
 * @Create: 2023/11/7 - 11:31 PM
 * @Version: v1.0
 */
public class UserServiceImpl implements UserService {
    @Override
    public void getUser() {
        System.out.println("獲取user...");
    }
}

②配置bean

使用bean標籤的autowire屬性設定自動裝配效果

自動裝配方式:byType

byType:根據型別匹配IOC容器中的某個相容型別的bean,為屬性自動賦值

若在IOC中,沒有任何一個相容型別的bean能夠為屬性賦值,則該屬性不裝配,即值為預設值null

若在IOC中,有多個相容型別的bean能夠為屬性賦值,則丟擲異常NoUniqueBeanDefinitionException

<?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="userService" class="com.mcode.autowire.service.impl.UserServiceImpl"/>

    <bean id="userController" class="com.mcode.autowire.controller.UserController" autowire="byType"/>

</beans>

自動裝配方式:byName

byName:將自動裝配的屬性的屬性名,作為bean的id在IOC容器中匹配相對應的bean進行賦值

<?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="userService" class="com.mcode.autowire.service.impl.UserServiceImpl"/>
    <bean id="userController" class="com.mcode.autowire.controller.UserController" autowire="byName"/>

</beans>

③測試

    @Test
    public void testAutoWireByXML(){
        ApplicationContext ac = new ClassPathXmlApplicationContext("spring-autowire.xml");
        UserController userController = ac.getBean(UserController.class);
        userController.getUser();
    }

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