[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

 1 package com.how2java.pojo;
 2
 3 import org.springframework.stereotype.Component;
 4
 5 @Component("c")
 6 public class Category {
 7
 8     public int getId() {
 9         return id;
10     }
11     public void setId(int id) {
12         this.id = id;
13     }
14     public String getName() {
15         return name;
16     }
17     public void setName(String name) {
18         this.name = name;
19     }
20     private int id;
21     private String name = "catagory 1";
22 }

Product.java

 1 package com.how2java.pojo;
 2
 3 import org.springframework.beans.factory.annotation.Autowired;
 4 import org.springframework.stereotype.Component;
 5
 6 @Component("p")
 7 public class Product {
 8     private int id;
 9     private String name = "product 1";
10
11     @Autowired
12     private Category category;
13     public int getId() {
14         return id;
15     }
16     public void setId(int id) {
17         this.id = id;
18     }
19     public String getName() {
20         return name;
21     }
22     public void setName(String name) {
23         this.name = name;
24     }
25     public Category getCategory() {
26         return category;
27     }
28     public void setCategory(Category category) {
29         this.category = category;
30     }
31 }

TestSpring.java

 1 package com.how2java.test;
 2
 3 import org.springframework.context.ApplicationContext;
 4 import org.springframework.context.support.ClassPathXmlApplicationContext;
 5
 6 import com.how2java.pojo.Product;
 7
 8 public class TestSpring {
 9
10     public static void main(String[] args) {
11         ApplicationContext context = new ClassPathXmlApplicationContext(new String[] { "applicationContext.xml" });
12
13         Product p = (Product) context.getBean("p");
14         System.out.println(p.getName());
15         System.out.println(p.getCategory().getName());
16     }
17 }

applicationContext.xml

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <beans xmlns="http://www.springframework.org/schema/beans"
 3     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:aop="http://www.springframework.org/schema/aop"
 4     xmlns:tx="http://www.springframework.org/schema/tx" xmlns:context="http://www.springframework.org/schema/context"
 5     xsi:schemaLocation="
 6    http://www.springframework.org/schema/beans
 7    http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
 8    http://www.springframework.org/schema/aop
 9    http://www.springframework.org/schema/aop/spring-aop-3.0.xsd
10    http://www.springframework.org/schema/tx
11    http://www.springframework.org/schema/tx/spring-tx-3.0.xsd
12    http://www.springframework.org/schema/context
13    http://www.springframework.org/schema/context/spring-context-3.0.xsd">
14
15     <context:annotation-config/>
16     <bean name="c" class="com.how2java.pojo.Category">
17         <property name="name" value="category 1" />
18     </bean>
19     <bean name="p" class="com.how2java.pojo.Product">
20         <property name="name" value="product1" />
21 <!--         <property name="category" ref="c" /> -->
22     </bean>
23
24 </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

1 package com.how2java.service;
2
3 public class ProductService {
4     public void doSomeService() {
5         System.out.println("doSomeService");
6     }
7 }

LoggerAspect.java

 1 package com.how2java.aspect;
 2
 3 import org.aopalliance.intercept.Joinpoint;
 4 import org.aspectj.lang.ProceedingJoinPoint;
 5
 6 public class LoggerAspect {
 7     public Object log(ProceedingJoinPoint joinPoint) throws Throwable{
 8         System.out.println("start log:" + joinPoint.getSignature().getName());
 9         Object object = joinPoint.proceed();
10         System.out.println("end log:" + joinPoint.getSignature().getName());
11         return object;
12     }
13 }

TestSpring.java

 1 package com.how2java.test;
 2
 3 import org.springframework.context.ApplicationContext;
 4 import org.springframework.context.support.ClassPathXmlApplicationContext;
 5
 6 import com.how2java.service.ProductService;
 7
 8 public class TestSpring {
 9     public static void main(String[] args) {
10         ApplicationContext context = new ClassPathXmlApplicationContext(new String[] { "applicationContext.xml" });
11         ProductService s = (ProductService) context.getBean("s");
12         s.doSomeService();
13     }
14 }

applicationContext.xml

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <beans xmlns="http://www.springframework.org/schema/beans"
 3     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 4     xmlns:aop="http://www.springframework.org/schema/aop"
 5     xmlns:tx="http://www.springframework.org/schema/tx"
 6     xmlns:context="http://www.springframework.org/schema/context"
 7     xsi:schemaLocation="
 8    http://www.springframework.org/schema/beans
 9    http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
10    http://www.springframework.org/schema/aop
11    http://www.springframework.org/schema/aop/spring-aop-3.0.xsd
12    http://www.springframework.org/schema/tx
13    http://www.springframework.org/schema/tx/spring-tx-3.0.xsd
14    http://www.springframework.org/schema/context
15    http://www.springframework.org/schema/context/spring-context-3.0.xsd">
16
17     <bean name="s" class="com.how2java.service.ProductService">
18     </bean>
19
20      <bean id="loggerAspect" class="com.how2java.aspect.LoggerAspect"/>
21
22      <aop:config>
23          <aop:pointcut id="loggerCutpoint"
24              expression=
25              "execution(* com.how2java.service.ProductService.*(..))"/>
26
27          <aop:aspect id="logAspect" ref="loggerAspect">
28              <aop:around pointcut-ref="loggerCutpoint" method="log"/>
29          </aop:aspect>
30      </aop:config>
31
32 </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