[Java Web] Spring

Posted 2020-12-29 arseneyao

一、概述

Spring是一种轻量级企业应用开发框架，提供了控制反转（IoC）和面向切面编程（AOP）技术。

 

二、控制反转

控制反转是指程序之间的关系不再直接使用代码进行控制，而是使用容器进行控制。如此控制权就由程序代码转移到外部容器，控制权转移就是控制反转。由于程序组件之间的依赖关系是由容器控制的。在程序运行期间，通过容器动态地将依赖关系注入到组件中就是依赖注入，依赖注入是反转控制的一种形式。在IoC中通过配置文件描述对象之间的依赖关系，而不再使用代码调用其他类对象。在程序运行期间，IoC容器通过加载配置文件，将对象之间的依赖关系注入。

BeanFactory提供了Spring的核心功能，采用工厂模式实现反转控制和依赖注入。通过读取XML文件或属性文件读取JavaBean的定义，从而实现JavaBean的创建、配置和管理。一般将BeanFactory作为容器来获取JavaBean。使用BeanFactory的子接口ApplicationContext读取XML配置文件并加载JavaBean。

//Message.java
package bean;

public class Message {
    private String content;

    public String getContent() {
        return content;
    }

    public void setContent(String content) {
        this.content = content;
    }
}


<!-- 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"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
    <bean class="bean.Message" name="message">
        <property name="content" value="this is a spring test!"/>
    </bean>
</beans>




//Solution.java
import bean.Message;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class Solution {
    public static void main(String[] args) {
        ApplicationContext context = new ClassPathXmlApplicationContext("beans.xml");
        Message message = (Message) context.getBean("message");
        System.out.println(message.getContent());
    }
}

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赋值注入。

//Company.java
package bean;

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

    public int getId() {
        return id;
    }

    public String getName() {
        return name;
    }

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

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

    @Override
    public String toString() {
        return String.format("[%d: %s]", id, name);
    }
}


//Worker.java
package bean;

import java.util.List;

public class Worker {
    private int id;
    private String name;
    private Company company;
    private List<String> like;

    public int getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public Company getCompany() {
        return company;
    }

    public List<String> getLike() {
        return like;
    }

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

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

    public void setCompany(Company company) {
        this.company = company;
    }

    public void setLike(List<String> like) {
        this.like = like;
    }

    @Override
    public String toString() {
        return String.format("[%d: %s] works at %s and likes %s",
                id, name, company, like);
    }
}




//spring-config.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="comp" class="bean.Company">
        <property name="id" value="101"/>
        <property name="name" value="Google"/>
    </bean>
    <bean id="worker" class="bean.Worker">
        <property name="id" value="1001"/>
        <property name="name" value="Lee"/>
        <property name="company" ref="comp"/>
        <property name="like">
            <list>
                <value>Coding</value>
                <value>Game</value>
                <value>Basketball</value>
            </list>
        </property>
    </bean>
</beans>




//Solution.java
import bean.Worker;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class Solution {
    public static void main(String[] args) {
        ApplicationContext context = new ClassPathXmlApplicationContext("spring-config.xml");
        Worker worker = (Worker) context.getBean("worker");
        System.out.println(worker.toString());
    }
}

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构造器注入。

//Company.java
package bean;

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

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

    @Override
    public String toString() {
        return String.format("[%d: %s]", id, name);
    }
}



//Worker.java
package bean;

import java.util.List;

public class Worker {
    private int id;
    private String name;
    private Company company;
    private List<String> like;

    public Worker(int id, String name, Company company, List<String> like) {
        this.id = id;
        this.name = name;
        this.company = company;
        this.like = like;
    }

    @Override
    public String toString() {
        return String.format("[%d: %s] works at %s and likes %s",
                id, name, company, like);
    }
}



//spring-config.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="comp" class="bean.Company">
        <constructor-arg index="0" value="101"/>
        <constructor-arg index="1" value="Google"/>
    </bean>
    <bean id="worker" class="bean.Worker">
        <constructor-arg index="0" value="1001"/>
        <constructor-arg index="1" value="Lee"/>
        <constructor-arg index="2" ref="comp"/>
        <constructor-arg index="3">
            <list>
                <value>Coding</value>
                <value>Game</value>
                <value>Basketball</value>
            </list>
        </constructor-arg>
    </bean>
</beans>



//Solution.java
import bean.Worker;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class Solution {
    public static void main(String[] args) {
        ApplicationContext context = new ClassPathXmlApplicationContext("spring-config.xml");
        Worker worker = (Worker) context.getBean("worker");
        System.out.println(worker.toString());
    }
}

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