Spring核心概念之Ioc
Spring核心概念之Ioc
一、初识Spring之Ioc
Spring是一个轻量级的企业级开源框架,Spring框架的核心是一个Ioc容器。Ioc (Inversion of Control)又称"控制反转",是面向对象编程中的一种设计原则,用来降低程序代码之间的耦合度。
实战演练:使用Spring Ioc实现业务层和数据访问层解耦合。
1.定义数据访问层接口:UserDao
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package com.jbit.fsd.dao;
import java.util.List;
import com.jbit.fsd.entity.User;
public interface UserDao {
public List<User> getAll();
}
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2.定义了业务访问层接口:UserService
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package com.jbit.fsd.service;
import java.util.List;
import com.jbit.fsd.entity.User;
public interface UserService {
public List<User> getAll();
}
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3.定义了数据访问层接口实习类:UserDaoImpl
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package com.jbit.fsd.dao.impl;
import java.util.ArrayList;
import java.util.List;
import com.jbit.fsd.dao.UserDao;
import com.jbit.fsd.entity.User;
public class UserDaoImpl implements UserDao {
@Override
public List<User> getAll() {
//操作数据库读到所有数据
List<User> list= new ArrayList<User>();
list.add( new User());
list.add( new User());
list.add( new User());
return list;
}
}
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4.定义数据访问层接口实现类:UserServiceImpl
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package com.jbit.fsd.service.impl;
import java.util.List;
import com.jbit.fsd.dao.UserDao;
import com.jbit.fsd.entity.User;
import com.jbit.fsd.service.UserService;
public class UserServiceImpl implements UserService{
private UserDao dao;
//通过spring注入进来
public void setDao(UserDao dao) {
this .dao = dao;
}
@Override
public List<User> getAll() {
// TODO Auto-generated method stub
return dao.getAll();
}
}
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5.在spring配置文件中配置Bean并注入业务实现类UserServiceImpl
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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:aop= "http://www.springframework.org/schema/aop"
xmlns:tx= "http://www.springframework.org/schema/tx"
xsi:schemaLocation="
http: //www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
http: //www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-2.5.xsd
http: //www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-2.5.xsd">
<!-- 以面向接口思想编程实现解耦和 -->
<bean id= "userDao" class = "com.jbit.fsd.dao.impl.UserDaoImpl" >
</bean>
<bean id= "userServiceImpl" class = "com.jbit.fsd.service.impl.UserServiceImpl" >
<!-- 需要注意是是这里调用setDao()方法 -->
<property name= "dao" ref= "userDao" ></property> <!-- 属性注入 -->
</bean>
</beans>
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6.测试类入口:
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package com.jbit.fsd.test;
import java.util.List;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import com.jbit.fsd.dao.UserDao;
import com.jbit.fsd.entity.User;
import com.jbit.fsd.service.UserService;
public class Test {
/**
*
* Description:
* @param
* @author xiazhongwei
* @data 2016:下午12:18:37
* @return
*/
public static void main(String[] args) {
ApplicationContext ac= new ClassPathXmlApplicationContext( "applicationContext.xml" );
UserService service=(UserService) ac.getBean( "userServiceImpl" );
List<User> list=service.getAll();
System.out.println(list.size()+ "********************" );
}
}
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上面的小例子需要Spring核心jar的支持:可到官网下载
说明:
1.Spring为dao属性赋值是通过setDao()方法实现的,而非直接为dao属性赋值,若属性为dao,但是setter方法为setUserDao,Spring配置文件应该写成name="userDao",而非name="dao";
2.除了使用ApplicationContext及其实现类,还可以通过BeanFactory接口实现类对Bean组件实施管理,ApplicationContext建立在BeanFactory的基础之上,可以对企业级开发提供更全名的支持。
使用上面的方法通过spring的setter访问器实现对属性的赋值,这种方法称设置注入,除此之外,spring还提供了通过构造方法赋值,这种称构造注入。
定义业务实现类UserServiceImplByConstructor
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package com.jbit.fsd.service.impl;
import java.util.List;
import com.jbit.fsd.dao.UserDao;
import com.jbit.fsd.entity.User;
import com.jbit.fsd.service.UserService;
public class UserServiceImplByConstructor implements UserService {
private UserDao dao;
// 定义有参的构造方法JVM不会自定义无参的构造方法,需要手动加入
public UserServiceImplByConstructor(){
}
// 用于为dao属性赋值的构造方法
public UserServiceImplByConstructor(UserDao dao){
this .dao = dao;
}
@Override
public List<User> getAll() {
return dao.getAll();
}
}
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spring配置文件中的配置:
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<?xml version= "1.0" encoding= "UTF-8" ?>
<!--
- Application context definition for JPetStore's business layer.
- Contains bean references to the transaction manager and to the DAOs in
- dataAccessContext-local/jta.xml (see web.xml's "contextConfigLocation" ).
-->
<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"
xsi:schemaLocation="
http: //www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
http: //www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-2.5.xsd
http: //www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-2.5.xsd">
<!-- 以面向接口思想编程实现解耦和 -->
<bean id= "userDao" class = "com.jbit.fsd.dao.impl.UserDaoImpl" >
</bean>
<bean id= "userServiceImplByConstructor" class = "com.jbit.fsd.service.impl.UserServiceImplByConstructor" >
<!-- 通过定义的单参数构造为业务层的dao属性赋值 -->
<constructor-arg>
<!-- 引用id为userDao的对象为dao属性赋值 -->
<ref bean= "userDao" />
</constructor-arg>
</bean>
</beans>
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说明:一个<constructor-arg>元素表示一个构造参数,且使用时不区分顺序,当构造方法的参数出现混淆,无法区分时,可以通过<constructor-arg>元素的index属性来指定该参数的位置索引,位置从0开始,<constructor-arg>元素还提供了type属性用来指定参数的类型,避免字符串和基本类型的混淆。
二、不同类型参数的注入方法
1.注入直接量(基本类型、字符串)
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<?xml version= "1.0" encoding= "UTF-8" ?>
<!--
- Application context definition for JPetStore's business layer.
- Contains bean references to the transaction manager and to the DAOs in
- dataAccessContext-local/jta.xml (see web.xml's "contextConfigLocation" ).
-->
<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"
xsi:schemaLocation="
http: //www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
http: //www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-2.5.xsd
http: //www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-2.5.xsd">
<!-- 以面向接口思想编程实现解耦和 -->
<bean id= "userDao" class = "com.jbit.fsd.dao.impl.UserDaoImpl" >
</bean>
<bean id= "userServiceImpl" class = "com.jbit.fsd.service.impl.UserServiceImpl" >
<!-- 需要注意是是这里调用setDao()方法 -->
<span style= "color: rgb(255, 0, 0);" ><property name= "dao" ref= "userDao" ></property> </span> <!-- 属性注入 -->
</bean>
<bean id= "userServiceImpl" class = "com.jbit.fsd.service.impl.UserServiceImpl" >
<property name= "username" >
</property>
<!-- 注入直接量 -->
<value>张三</value>
</bean>
<bean id= "userServiceImpl" class = "com.jbit.fsd.service.impl.UserServiceImpl" >
<!-- 需要注意是是这里调用setDao()方法 -->
<span style= "color: rgb(255, 0, 0);" ><property name= "dao" >
<ref local= "userDao" ></ref>
</property></span>
</bean>
<bean id= "userServiceImplByConstructor" class = "com.jbit.fsd.service.impl.UserServiceImplByConstructor" >
<!-- 通过定义的单参数构造为业务层的dao属性赋值 -->
<constructor-arg>
<!-- 引用id为userDao的对象为dao属性赋值 -->
<ref bean= "userDao" />
</constructor-arg>
</bean>
</beans>
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上面的代码看:local属性和bean属性的用法和像,区别在于:当把spring的配置文件拆分为多个时,使用local属性只能在同一个配文件中检索Bean的id,而使用bean属性可以在其他配置文件中检索id。
2.使用内部Bean
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<bean id= "userServiceImpl" class = "com.jbit.fsd.service.impl.UserServiceImpl" >
<!-- 需要注意是是这里调用setDao()方法 -->
<property name= "dao" >
<bean class = "com.pb.dao.impl.UserDaoimpl" >
</property> <!-- 属性注入 -->
</bean>
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如果属性中包含特殊字符如(&,<,>)等可将特殊字符替换为实体引用,如<替换为&It.
3.注入集合类型的属性
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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:aop= "http://www.springframework.org/schema/aop"
xmlns:tx= "http://www.springframework.org/schema/tx"
xsi:schemaLocation="
http: //www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
http: //www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-2.5.xsd
http: //www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-2.5.xsd">
<!-- 以面向接口思想编程实现解耦和 -->
<bean id= "userDao" class = "com.jbit.fsd.dao.impl.UserDaoImpl" >
</bean>
<bean id= "user" class = "com.pb.eneity.User" >
<property name= "hobbies" ><br> <!--list类型变量的注入 -->
<list>
<value>足球</value>
<value>篮球</value>
</list>
</property>
</bean>
<bean id= "user" class = "com.pb.eneity.User" >
<property name= "hobbies" ><br> <!--ser类型变量的注入-->
<set>
<value>足球</value>
<value>篮球</value>
</set>
</property>
</bean>
<bean id= "user" class = "com.pb.eneity.User" >
<property name= "hobbies" ><br> <!-- map类型变量的注入 -->
<map>
<entry>
<key><value>username</value></key>
<ref bean= "com.pb.entity.User" ></ref>
</entry>
</map>
</property>
</bean>
</beans>
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三、使用多种方式简化spring Ioc的配置
1.使用p命名空间注入Bean属性
使用p命名空间改进配置,改进前先添加p命名空间是声明。
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<?xml version= "1.0" encoding= "UTF-8" ?>
<!--
- Application context definition for JPetStore's business layer.
- Contains bean references to the transaction manager and to the DAOs in
- dataAccessContext-local/jta.xml (see web.xml's "contextConfigLocation" ).
-->
<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"
<span style= "color: rgb(255, 0, 0);" >xmlns:aop= "http://www.springframework.org/schema/p" </span>
xsi:schemaLocation="
http: //www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
http: //www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-2.5.xsd
http: //www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-2.5.xsd">
<bean id= "userDao" class = "com.jbit.fsd.dao.impl.UserDaoImpl" <span style= "color: rgb(255, 0, 0);" > p:age= "18" p:username= "xiaoming" </span>>
</bean>
</beans>
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使用p命名空间简化配对效果明显,使用语法总结:
1.对于直接量(基本数据类型、字符串)属性,使用方式如下:
p:属性名=“属性值”
2.对于引用Bean的属性,使用方式如下:
p:属性名-ref="Bean的id"
2.Spring配置文件实现自动装配
<bean>元素的autowire属性提供了一种自动注入的依赖对象的机制,配置Bean时不需要做任何显示的指定,spring会自动查找符合条件的依赖对象并实施注入。
<bean id="userService" class="com.pb.serviceImp.UserServiceImpl" autowire="byType">
spring提供了几种自动装配的类型:
1.no:默认值,Spring默认不进行自动装配,必须显示的指定依赖对象
2.byName: 根据属性名自动装配,Spring自动查找与属性名相同的id,如果找到,则自动注入,否则什么也不做。
3.byType:根据属性的类型自动装配,Spring自动查找与属性类型相同Bean,如果找到唯一的那个,则自动注入,如果找到多个与属性类型相同的Bean,则抛出异常,如果没找到则什么也不做。
4.constructor:和byType类似,不过他针对构造方法,如果spring找到一个Bean和构造方法的参数类型像匹配,则通过构造方法注入到依赖对象,如果没有,则抛异常。
如果每个Bean都设置autowire属性也是挺麻烦的,spring提供了default-autowire属性,设置全局的自动装配。
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<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:aop= "http://www.springframework.org/schema/p"
xsi:schemaLocation="
http: //www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
http: //www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-2.5.xsd
http: //www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-2.5.xsd"
default -autowire= "byType" >
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