spring依赖注入引发的一点思考 喜欢ヅ旅行 2021-06-24 15:58 393阅读 0赞 java中bean 分为普通的java bean和spring的bean两种。 1)通过spring的配置文件或者注解,在进程启动时由spring对其初始化、并最终最终放到spring容器中,这就是spring的bean,否则就是java bean。 2)如果是spring的bean,那么在代码中直接getbean("beanname")使用即可;如果是普通的java bean 使用时直接 new,产生一个实例即可。 一、下面举一个spring bean进行依赖注入的最简单例子: 1、service接口和类: 1)demoService接口和实现类: public interface IDemoService { public String sayHello(String a); } 实现类: import org.springframework.beans.factory.annotation.Autowired; import org.springframework.stereotype.Service; @Service public class DemoService implements IDemoService { @Autowired private ITestService testService; @Override public String sayHello(String a) { System.out.println(testService.test("test")); return "hello"+a; } } 说明:该service实现类中又使用注解(@AutoWired)依赖注入了另一个spring bean ITestService 2)TestService接口和实现类: public interface ITestService { public String test(String test); } 实现类: @Service public class TestService implements ITestService { @Override public String test(String test) { return "test:"+test; } } 2、pom.xml文件: <!-- spring --> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-core</artifactId> <version>${org.springframework.version}</version> <type>jar</type> <scope>compile</scope> </dependency> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-beans</artifactId> <version>${org.springframework.version}</version> <type>jar</type> <scope>compile</scope> </dependency> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-context</artifactId> <version>${org.springframework.version}</version> <type>jar</type> <scope>compile</scope> </dependency> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-context-support</artifactId> <version>${org.springframework.version}</version> </dependency> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-orm</artifactId> <version>${org.springframework.version}</version> </dependency> <dependency> <groupId>org.aspectj</groupId> <artifactId>aspectjweaver</artifactId> <version>1.8.2</version> </dependency> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-test</artifactId> <version>${org.springframework.version}</version> </dependency> <dependency> <groupId>org.quartz-scheduler</groupId> <artifactId>quartz</artifactId> <version>2.2.0</version> </dependency> 3、application.xml文件: <?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:context="http://www.springframework.org/schema/context" xmlns:mvc="http://www.springframework.org/schema/mvc" xmlns:tx="http://www.springframework.org/schema/tx" xmlns:jaxws="http://cxf.apache.org/jaxws" xmlns:task="http://www.springframework.org/schema/task" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-3.2.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.2.xsd http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc-3.2.xsd http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-3.2.xsd http://www.springframework.org/schema/task http://www.springframework.org/schema/task/spring-task-3.2.xsd"> <!-- 注解方式的aop <aop:aspectj-autoproxy proxy-target-class="true"/> --> <task:annotation-driven/> <context:component-scan base-package="cn.eud.nuc.archiveTest.service" /> <!-- 自动搜索Sping的注解类--> <context:component-scan base-package="cn.eud.nuc" > <context:exclude-filter type="annotation" expression="org.springframework.stereotype.Controller"/> </context:component-scan> </beans> 4、测试程序: public class App { private static ApplicationContext ac; public static void main(String[] args) { ac = new ClassPathXmlApplicationContext( new String[] { "classpath:application.xml"}); IDemoService demoService = (IDemoService)ac.getBean("demoService"); System.out.println(demoService.sayHello(" sfsd")); } } 5、说明: 1)在App主类中,只能通过ac.getBean()的方式获取demoService 的spring bean来使用;下面这种方式使用是错误的。 @Service public class App{ @Autowired private IDemoService demoService; private static ApplicationContext ac; public static void main(String[] args) { ac = new ClassPathXmlApplicationContext( new String[] { "classpath:application.xml"}); } private void test() { demoService.sayHello("sss:"); } } 2)除了使用上面注解的方式去注入,也可以使用配置文件的方式来实现: 去掉TestService实现类的注解, public class TestService implements ITestService { @Override public String test(String test) { return "test:"+test; } } 在application.xml中添加: <bean class="cn.eud.nuc.archiveTest.service.TestService" /> 3)在DemoService实现类中,使用@AutoWired注入ITestService,spring会在进程启动的时候找ITestService的实现类,将其初始化,然后再将其注入到DemoService中,这样,就可以在DemoService中直接使用了。 二、使用代理的方式完成spring bean的注入: 1、service类: 1)demoService接口和实现类: public interface IDemoService { public String sayHello(String a); } 实现类: import org.springframework.beans.factory.annotation.Autowired; import org.springframework.stereotype.Service; @Service public class DemoService implements IDemoService { @Autowired private ITestService testService; @Override public String sayHello(String a) { System.out.println(testService.test("test")); return "hello"+a; } } 说明:该service实现类中又使用注解(@AutoWired)依赖注入了另一个spring bean ITestService 2)TestService接口和实现类: public interface ITestService { public String test(String test); } 这个接口没有实现类,下面我们使用一个动态代理类来代理这个接口(底层代理类会实现该接口),并将这个动态代理类注入到spring容器中,并初始化,然后注入到DemoService中。 2、代理类: import java.lang.reflect.InvocationHandler; import java.lang.reflect.Method; import java.lang.reflect.Proxy; import org.springframework.beans.factory.FactoryBean; import org.springframework.beans.factory.InitializingBean; import cn.eud.nuc.archiveTest.service.ITestService; @SuppressWarnings({ "rawtypes" }) public class ServiceProxy implements FactoryBean,InitializingBean{ private Object proxyClient; private Class<?> objectClass; @Override public void afterPropertiesSet() throws Exception { final ClassLoader classLoader = Thread.currentThread().getContextClassLoader(); objectClass = classLoader.loadClass("cn.eud.nuc.archiveTest.service.ITestService"); proxyClient = Proxy.newProxyInstance(classLoader, new Class[] { objectClass }, new InvocationHandler() { @Override public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { try { Class<ITestService> testClass = (Class<ITestService>)classLoader.loadClass("cn.eud.nuc.archiveTest.service.TestService"); ITestService newInstance = testClass.newInstance(); System.out.println("proxy:"+newInstance.test("a")); return method.invoke(newInstance, args); } catch (ClassNotFoundException e) { throw e; } } }); } @Override public Object getObject() throws Exception { return proxyClient; } @Override public Class<?> getObjectType() { return objectClass; } @Override public boolean isSingleton() { return true; } } 1)说明: 这个类首先实现了InitializingBean接口,目的是spring在加载这个类(通过application.xml配置文件)的时候调用afterPropertiesSet() 方法来实现代理类的创建;其次,该类也实现了FactoryBean接口,目的是供spring注入的时候返回正确的bean类型。 2)我们再随便写一个接口的实现类(不添加到spring中) package cn.eud.nuc.archiveTest.service; public class TestService implements ITestService { @Override public String test(String test) { return "test:"+test; } } 3、application.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:context="http://www.springframework.org/schema/context" xmlns:mvc="http://www.springframework.org/schema/mvc" xmlns:tx="http://www.springframework.org/schema/tx" xmlns:jaxws="http://cxf.apache.org/jaxws" xmlns:task="http://www.springframework.org/schema/task" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-3.2.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.2.xsd http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc-3.2.xsd http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-3.2.xsd http://www.springframework.org/schema/task http://www.springframework.org/schema/task/spring-task-3.2.xsd"> <!-- 注解方式的aop <aop:aspectj-autoproxy proxy-target-class="true"/> --> <task:annotation-driven/> <context:component-scan base-package="cn.eud.nuc.archiveTest.service" /> <!-- 自动搜索Sping的注解类--> <context:component-scan base-package="cn.eud.nuc" > <context:exclude-filter type="annotation" expression="org.springframework.stereotype.Controller"/> </context:component-scan> <bean class="cn.eud.nuc.archiveTest.ServiceProxy" /> </beans> 4、测试类:同上 5、说明: spring在依赖注入的时候,需要找到@autoWired接口的实现类去注入。上面两个实例中, 1)第一种:将一个接口的实现类注册到spring容器中,spring自动去进行依赖注入(也是spring推荐正规的方式), 2)第二种:使用了一个自定义代理类,在代理类找到接口然后动态代理这个接口,然后将代理类交给spring去管理,这样代理类就相当于实现了该接口的一个类,并注入到DemoService中去使用
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