SPR4: 依赖注入的三种方式

4.1 构造器注入

即在配置文件中，通过bean标签，使用 constructor-arg 子标签实现。

4.2 setter()注入

4.2.1 简介

依赖注入一词，依赖指的是bean对象的创建依赖于Spring容器。注入则指的是bean里面的属性值，由SPring传递。

4.2.2 环境配置

Address:

package com.yun.pojo;public class Address {private String address;public String getAddress() {return address;}public void setAddress(String address) {this.address = address;}
}

Student:

package com.yun.pojo;import java.util.*;public class Student {private String name;private Address address;private String[] books;private List<String> hobbies;private Map<String,String> card;private Set<String> games;private String wife;private Properties info;public String getName() {return name;}public void setName(String name) {this.name = name;}public Address getAddress() {return address;}public void setAddress(Address address) {this.address = address;}public String[] getBooks() {return books;}public void setBooks(String[] books) {this.books = books;}public List<String> getHobbies() {return hobbies;}public void setHobbies(List<String> hobbies) {this.hobbies = hobbies;}public Map<String, String> getCard() {return card;}public void setCard(Map<String, String> card) {this.card = card;}public Set<String> getGames() {return games;}public void setGames(Set<String> games) {this.games = games;}public String getWife() {return wife;}public void setWife(String wife) {this.wife = wife;}public Properties getInfo() {return info;}public void setInfo(Properties info) {this.info = info;}@Overridepublic String toString() {return "Student{" +"name='" + name + '\'' +", address=" + address +", books=" + Arrays.toString(books) +", hobbies=" + hobbies +", card=" + card +", games=" + games +", wife='" + wife + '\'' +", info=" + info +'}';}
}

applicationContext.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/beanshttps://www.springframework.org/schema/beans/spring-beans.xsd"><bean id="student" class="com.yun.pojo.Student"><property name="name" value="张三"/></bean></beans>

测试接口：

package com.yun;import com.yun.pojo.Student;
import org.junit.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;public class MyTest {@Testpublic void test(){ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");Student student = (Student)context.getBean("student");System.out.println(student);}
}

4.2.3 各类型的依赖注入

普通类型注入：

    <bean id="student" class="com.yun.pojo.Student"><property name="name" value="张三"/></bean>

对象属性注入：

    <bean id="address1" class="com.yun.pojo.Address"><property name="address" value="武汉"/></bean><bean id="student" class="com.yun.pojo.Student"><!--    对象属性注入--><property name="address" ref="address1"/></bean>

数组属性注入：

    <bean id="student" class="com.yun.pojo.Student">
<!--        数组注入--><property name="books"><array><value>斗破苍穹</value><value>斗罗大陆</value><value>善良的死神</value><value>仙逆</value></array></property></bean>

List属性注入：

    <bean id="student" class="com.yun.pojo.Student"><!--list属性注入--><property name="hobbies"><list><value>打游戏</value><value>听歌</value><value>看电影</value></list></property></bean>

map属性注入：

    <bean id="student" class="com.yun.pojo.Student"><!--        map属性注入-->  <property name="card"><map><entry key="身份证" value="中国公民身份证"/><entry key="银行卡" value="中国农业银行储蓄卡"/><entry key="信用卡" value="建设银行龙卡"/></map></property></bean>

Set属性注入：

    <bean id="student" class="com.yun.pojo.Student">
<!--        set属性注入--><property name="games"><set><value>绝地求生</value><value>GTA5</value></set></property></bean>

null属性注入：

    <bean id="student" class="com.yun.pojo.Student"><!--null属性注入--><property name="wife"><null/></property></bean>

Properties属性注入：

    <bean id="student" class="com.yun.pojo.Student">
<!--        Properties属性注入--><property name="info"><props><prop key="学号">202545877</prop><prop key="性别">男</prop></props></property></bean>

applicationContext.xml概览：

<?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/beanshttps://www.springframework.org/schema/beans/spring-beans.xsd"><bean id="address1" class="com.yun.pojo.Address"><property name="address" value="武汉"/></bean><bean id="student" class="com.yun.pojo.Student"><!--    普通类型注入--><property name="name" value="张三"/><!--    对象属性注入--><property name="address" ref="address1"/>
<!--        数组注入--><property name="books"><array><value>斗破苍穹</value><value>斗罗大陆</value><value>善良的死神</value><value>仙逆</value></array></property>
<!--        list属性注入--><property name="hobbies"><list><value>打游戏</value><value>听歌</value><value>看电影</value></list></property>
<!--        map属性注入--><property name="card"><map><entry key="身份证" value="中国公民身份证"/><entry key="银行卡" value="中国农业银行储蓄卡"/><entry key="信用卡" value="建设银行龙卡"/></map></property>
<!--        set属性注入--><property name="games"><set><value>绝地求生</value><value>GTA5</value></set></property>
<!--null属性注入--><property name="wife"><null/></property>
<!--        Properties属性注入--><property name="info"><props><prop key="学号">202545877</prop><prop key="性别">男</prop></props></property></bean>
</beans>

输出结果：

Student{name='张三', address=Address{address='武汉'}, books=[斗破苍穹, 斗罗大陆, 善良的死神, 仙逆], hobbies=[打游戏, 听歌, 看电影], card={身份证=中国公民身份证, 银行卡=中国农业银行储蓄卡, 信用卡=建设银行龙卡}, games=[绝地求生, GTA5], wife='null', info={学号=202545877, 性别=男}}

总结： arry、list、set、Properties 都是通过标签包含传值，并不是所谓的属性传值。

4.3 其他注入

4.3.1 P命名空间注入

约束：

xmlns:p="http://www.springframework.org/schema/p"

例子：

User.java

package com.yun.pojo;public class User {private String name;private int age;public String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}@Overridepublic String toString() {return "User{" +"name='" + name + '\'' +", age=" + age +'}';}
}

beans.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"xsi:schemaLocation="http://www.springframework.org/schema/beanshttps://www.springframework.org/schema/beans/spring-beans.xsd"><bean id="user" class="com.yun.pojo.User" p:name="李四" p:age="20"/></beans>
<!--导入约束，使用P标签-->

提示： 在Spring配置文件applicationContext.xml中，使用import导入bean.xml，或者将beans.xml作为Spring配置文件。

测试接口：

package com.yun;import com.yun.pojo.Student;
import com.yun.pojo.User;
import org.junit.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;public class MyTest {@Testpublic void test(){ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");User user = context.getBean("user", User.class);System.out.println(user);}
}

总结： p命名空间的依赖注入方式，本质上应该依旧是setter()注入。

4.3.2 c命名空间注入

User.java

package com.yun.pojo;public class User {private String name;private int age;public User(String name, int age) {this.name = name;this.age = age;}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}@Overridepublic String toString() {return "User{" +"name='" + name + '\'' +", age=" + age +'}';}
}

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:c="http://www.springframework.org/schema/c"xsi:schemaLocation="http://www.springframework.org/schema/beanshttps://www.springframework.org/schema/beans/spring-beans.xsd"><bean id="user" class="com.yun.pojo.User" c:name="王五" c:age="20"/></beans>

提示： 在Spring配置文件applicationContext.xml中，使用import导入bean.xml，或者将beans.xml作为Spring配置文件。

测试接口：

package com.yun;import com.yun.pojo.Student;
import com.yun.pojo.User;
import org.junit.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;public class MyTest {@Testpublic void test(){ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");User user = context.getBean("user", User.class);System.out.println(user);}
}

总结： c命名空间的依赖注入，本质上是构造器注入，因此实体类必须拥有有参构造。

4.4 bean的作用域

4.4.1 简介

Spring在创建bean对象之后，bean拥有着6种作用域：singeleton、prototype、request、session、application、websocket 。

4.4.2 singeleton单例模式

applicationContext.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:c="http://www.springframework.org/schema/c"xsi:schemaLocation="http://www.springframework.org/schema/beanshttps://www.springframework.org/schema/beans/spring-beans.xsd"><bean id="user" class="com.yun.pojo.User" c:name="王五" c:age="20" scope="singleton"/>
</beans>

测试接口：

package com.yun;import com.yun.pojo.Student;
import com.yun.pojo.User;
import org.junit.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;public class MyTest {@Testpublic void test(){ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");User user = context.getBean("user", User.class);User user1 = context.getBean("user", User.class);System.out.println(user==user1);}
}

提示： 输出结果为 true ，因为当前的Bean的作用域设置为singleton，并且Spring的bean作用域默认为singleton，所以，从容器内获取的实体类对象，都会受singleton单例的影响，只会创建一个实例。

4.4.3 prototype原型模式

applicationContext.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:c="http://www.springframework.org/schema/c"xsi:schemaLocation="http://www.springframework.org/schema/beanshttps://www.springframework.org/schema/beans/spring-beans.xsd"><bean id="user" class="com.yun.pojo.User" c:name="王五" c:age="20" scope="prototype"/>
</beans>

测试接口：

package com.yun;import com.yun.pojo.Student;
import com.yun.pojo.User;
import org.junit.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;public class MyTest {@Testpublic void test(){ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");User user = context.getBean("user", User.class);User user1 = context.getBean("user", User.class);System.out.println(user==user1);}
}

提示： 输出结果为 flase ，prototype 原型模式，每一次从容器内获取对象，都会创建一个新的对象。

4.4.4 request、session、application

此三种，只会在web开发中使用，具体详情需要查询官方文档。

写在最后，Spring学到这里，依旧有着不小的疑问，例如IOC注入到底有什么用；当我们使用bean进行依赖注入时，会不会把数据写死了；如果不是，那么IOC注入到底该怎么用。