[Java] Spring 使用

背景

• JavaEE 应用框架
• 基于IOC和AOP的结构J2EE系统的框架
• IOC（反转控制）：即创建对象由以前的程序员自己new 构造方法来调用，变成了交由Spring创建对象，是Spring的基础
• DI（依赖注入）：拿到的对象的属性，已经被注入好相关值了，直接使用即可
• AOP（Aspect Oriented Program 面向切面编程）
  • 功能分为核心业务功能（登录、增删改查）和周边功能（性能统计、日志、事务管理）
  • 周边功能在Spring的面向切面编程AOP思想里，即被定义为切面 
  • 面向切面编程AOP的思想里面，核心业务功能和切面功能分别独立进行开发
  • 然后把切面功能和核心业务功能 "编织" 在一起

IOC/DI

• 新建项目
• 添加依赖jar包
• 准备 pojo
• 配置 applicationContext.xml

Catagory.java

package com.how2java.pojo;

import org.springframework.stereotype.Component;

@Component("c")
public class Category {
 
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    private int id;
    private String name = "catagory 1";
}

Product.java

package com.how2java.pojo;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;

@Component("p")
public class Product {
    private int id;
    private String name = "product 1";
    
    @Autowired
    private Category category;
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public Category getCategory() {
        return category;
    }
    public void setCategory(Category category) {
        this.category = category;
    }
}

TestSpring.java

package com.how2java.test;

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

import com.how2java.pojo.Product;

public class TestSpring {

    public static void main(String[] args) {
        ApplicationContext context = new ClassPathXmlApplicationContext(new String[] { "applicationContext.xml" });
        
        Product p = (Product) context.getBean("p");
        System.out.println(p.getName());
        System.out.println(p.getCategory().getName());
    }
}

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:aop="http://www.springframework.org/schema/aop"
    xmlns:tx="http://www.springframework.org/schema/tx" xmlns:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="
   http://www.springframework.org/schema/beans
   http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
   http://www.springframework.org/schema/aop
   http://www.springframework.org/schema/aop/spring-aop-3.0.xsd
   http://www.springframework.org/schema/tx
   http://www.springframework.org/schema/tx/spring-tx-3.0.xsd
   http://www.springframework.org/schema/context     
   http://www.springframework.org/schema/context/spring-context-3.0.xsd">
  
    <context:annotation-config/>
    <bean name="c" class="com.how2java.pojo.Category">
        <property name="name" value="category 1" />
    </bean>
    <bean name="p" class="com.how2java.pojo.Product">
        <property name="name" value="product1" />
<!--         <property name="category" ref="c" /> -->
    </bean>
  
</beans>

AOP

• 辅助功能和核心业务功能彼此独立开发
• “登录”功能没有“性能统计”和“日志输出”也可以正常运行
• 如果有需要就把“日志输出”和“登录”功能编制在一起，实现登录时看到日志输出
• 辅助功能叫做切面，这种选择性的，低耦合的把切面和核心业务功能结合在一起的编程思想，就叫AOP

ProductService.java

package com.how2java.service;

public class ProductService {
    public void doSomeService() {
        System.out.println("doSomeService");
    }
}

LoggerAspect.java

package com.how2java.aspect;

import org.aopalliance.intercept.Joinpoint;
import org.aspectj.lang.ProceedingJoinPoint;

public class LoggerAspect {
    public Object log(ProceedingJoinPoint joinPoint) throws Throwable{
        System.out.println("start log:" + joinPoint.getSignature().getName());
        Object object = joinPoint.proceed();
        System.out.println("end log:" + joinPoint.getSignature().getName());
        return object;
    }
}

TestSpring.java

package com.how2java.test;

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

import com.how2java.service.ProductService;

public class TestSpring {
    public static void main(String[] args) {
        ApplicationContext context = new ClassPathXmlApplicationContext(new String[] { "applicationContext.xml" });
        ProductService s = (ProductService) context.getBean("s");
        s.doSomeService();
    }
}

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:aop="http://www.springframework.org/schema/aop"
    xmlns:tx="http://www.springframework.org/schema/tx"
    xmlns:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="
   http://www.springframework.org/schema/beans 
   http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
   http://www.springframework.org/schema/aop 
   http://www.springframework.org/schema/aop/spring-aop-3.0.xsd
   http://www.springframework.org/schema/tx 
   http://www.springframework.org/schema/tx/spring-tx-3.0.xsd
   http://www.springframework.org/schema/context      
   http://www.springframework.org/schema/context/spring-context-3.0.xsd">
 
    <bean name="s" class="com.how2java.service.ProductService">
    </bean>
     
     <bean id="loggerAspect" class="com.how2java.aspect.LoggerAspect"/>
     
     <aop:config>
         <aop:pointcut id="loggerCutpoint" 
             expression=
             "execution(* com.how2java.service.ProductService.*(..))"/>
         
         <aop:aspect id="logAspect" ref="loggerAspect">
             <aop:around pointcut-ref="loggerCutpoint" method="log"/> 
         </aop:aspect>
     </aop:config>
     
</beans>

• 通过xml文件配置的方式，把日志记录功能（切面）和核心业务编织在了一起，而TestSpring代码没有发生任何变化（解耦）

 

参考

Spring DI原理

https://www.cnblogs.com/gudazhi/p/11088439.html

Spring的IOC原理

https://www.cnblogs.com/superjt/p/4311577.html

步骤

https://www.cnblogs.com/vanl/p/5607534.html