依赖注入（DI）

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依赖注入（DI）

一、构造器注入

前面已经介绍过，参考 “IOC创建对象的方式”
在beans.xml中配置 <constructor-arg> 标签

二、Set方式注入【重点】

  • 依赖注入：Set注入
    • 依赖：bean对象的创建依赖于容器！
    • 注入：bean对象中的所有属性，由容器来注入！

实例：

  • dao
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package dao;

public class Address {
    private String address;

    public void setAddress(String address) {
        this.address = address;
    }

    @Override
    public String toString() {
        return "Address{" +
                "address='" + address + '\'' +
                '}';
    }
}
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package dao;

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

    public void setAddress(Address address) {
        this.address = address;
    }

    public void setBooks(String[] books) {
        this.books = books;
    }

    public void setHobbies(List<String> hobbies) {
        this.hobbies = hobbies;
    }

    public void setCard(Map<String, String> card) {
        this.card = card;
    }

    public void setGames(Set<String> games) {
        this.games = games;
    }

    public void setWife(String wife) {
        this.wife = wife;
    }

    public void setInfo(Properties info) {
        this.info = info;
    }

    @Override
    public String toString() {
        return "Student{" +
                "name='" + name + '\'' +
                ", address=" + address +
                ", books=" + Arrays.toString(books) +
                ", hobbies=" + hobbies +
                ", card=" + card +
                ", games=" + games +
                ", wife='" + wife + '\'' +
                ", info=" + info +
                '}';
    }
}
  • beans.xml配置
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<?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="address" class="com.nichu.dao.Address">
        <property name="address" value="蓝星种花家"/>
    </bean>
    <bean id="student" class="com.nichu.dao.Student">
        <!--property里面的name是实体类中set/get方法的名字首字母小写-->
        <!--第一种：普通值注入，value        -->
        <property name="name" value="晒太阳的猫"/>
        <!--第二种：注入对象-->
        <property name="address" ref="address"/>
        <!--第三种：注入数组-->
        <property name="books">
            <array>
                <value>数学</value>
                <value>语文</value>
                <value>英语</value>
                <value>历史</value>
                <value>政治</value>
            </array>
        </property>
        <!--第四种：注入列表-->
        <property name="hobbies">
            <list>
                <value>小说</value>
                <value>音乐</value>
            </list>
        </property>
        <!--第五种：注入map-->
        <property name="card">
            <map>
                <entry key="银行卡" value="34321432143214213"/>
                <entry key="身份证" value="3213213213849384193249"/>
            </map>
        </property>
        <!--第六种：注入set-->
        <property name="games">
            <set>
                <value>荣耀</value>
                <value>吃鸡</value>
            </set>
        </property>
        <!--第七种：注入null-->
        <property name="wife">
            <null/>
        </property>
        <!--第八种：注入属性-->
        <property name="info">
            <props>
                <prop key="身高">163</prop>
                <prop key="体重">50</prop>
            </props>
        </property>
    </bean>

</beans>
  • 测试类
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import com.nichu.dao.Student;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class Mytest {
    public static void main(String[] args) {
        ApplicationContext context = new ClassPathXmlApplicationContext("beans.xml");
        Student student = context.getBean("student", Student.class);
        System.out.println(student);
    }
}

三、拓展方式注入

1. c命名空间注入

实现：c命名空间注入，通过构造器注入:constructor-args

  • dao
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package dao;

public class User {
    private int id;
    private String name;

    public User(int id, String name) {
        this.id = id;
        this.name = name;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", name='" + name + '\'' +
                '}';
    }
}
  • 在beans.xml配置文件中添加红框内的代码

  • bean配置文件写法
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<?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/beans
       http://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean id="user" class="com.nichu.dao.User" c:id="1" c:name="小明"/>

</beans>

  • 测试类
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import com.nichu.dao.Student;
import com.nichu.dao.User;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

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

注意：

  • 使用c命名空间时，要在xml里加上xmlns:c=“http://www.springframework.org/schema/c”
  • 如果配置bean时，没有用构造函数注入，那么pojo必须要有无参构造函数
  • 如果配置bean时，使用c命名空间注入全部的参数，那么pojo必须要有全参构造函数
  • 如果配置bean时，使用c命名空间注入部分的参数，那么pojo必须要有对应的部分参数的构造函数

2. p命名空间注入

实现：p命名空间注入，可以直接注入属性的值：property

  • dao
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package dao;

public class Teacher {
    private int id;
    private String name;

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

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

    @Override
    public String toString() {
        return "Teacher{" +
                "id=" + id +
                ", name='" + name + '\'' +
                '}';
    }
}
  • bean配置文件写法

在beans.xml配置文件中添加红框内的代码

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<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"
       xmlns:p="http://www.springframework.org/schema/p"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
        https://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean id="teacher" class="dao.Teacher" p:id="3" p:name="赵长远"></bean>
</beans>
  • 测试类
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package dao;

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

public class TeacherTest {
    @Test
    public void userTest(){
        ApplicationContext applicationContext = new ClassPathXmlApplicationContext("applicationContext.xml");
        Teacher teacher = (Teacher) applicationContext.getBean("teacher");
        System.out.println(teacher);
    }
}

注意

四、Bean的作用域

1. 单例模式（Spring默认机制）

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<bean id="teacher" class="dao.Teacher" p:id="3" p:name="赵" scope="singleton"></bean>

或者

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<bean id="teacher" class="dao.Teacher" p:id="3" p:name="赵"></bean>

2. 原型模式

  • 每次从容器中get的时候，都会产生一个新对象！
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<bean id="teacher" class="dao.Teacher" p:id="3" p:name="赵老师" scope="prototype"></bean>

3. 其他

  • 其余的request、session、application、这些只能在web开发中使用到！
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