术语
- Guice:整个框架的门面
- Injector:一个依赖的管理上下文
- Binder:一个接口和实现的绑定
- Module:一组Binder
- Provider:bean的提供者
- Key:Binder中对应一个Provider
- Scope:Provider的作用域
- Stage:运行方式(为了不同的要求)
使用示例
- public class FooApplication {
- public static void main(String[] args) {
- Injector injector = Guice.createInjector(
- new ModuleA(),
- new ModuleB(),
- . . .
- new FooApplicationFlagsModule(args)
- );
- // Now just bootstrap the application and you're done
- FooStarter starter = injector.getInstance(FooStarter.class);
- starter.runApplication();
- }
- }
关于Stage以及如何选择?
stage分为三种,是三个不同场景下选择对应的值,Stage.TOOL时一些操作则不会支持,例如:java.lang.UnsupportedOperationException:Injector.injectMembers(Object) is not supported in Stage.TOOL
- TOOL(最小代价,有些功能会无法使用)
- DEVELOPMENT(快速启动,但不会做校验)
- PRODUCTION(异常检查与性能,启动会比较慢)
- Guice.createInjector(Stage.PRODUCTION, new ModuleA());
- Guice.createInjector(new ModuleA());//默认DEVELOPMENT
Module(模块)
Module内利用BindingBuilder生成Binder,如何实现一个Module?
- public class EventModule extends AbstractModule {
- @Override
- protected void configure() {
- <span style="white-space:pre"> </span>// 绑定接口与实现
- <span style="white-space:pre"> </span>bind(EventBusManager.class).annotatedWith(Names.named("eventBusManager")).to(EventBusManager.class);
- }
- }
绑定时如果是实现类绑定实现类会报错,但如果加个别名的话就没问题
几种bind方式
- bind(EventService.class).to(SpringEventService.class);
- bind(EventService.class).toInstance(new SpringEventService());
- bind(SpringEventService.class).asEagerSingleton();
- bind(EventService.class).toProvider(new Provider<EventService>(){
- @Override
- public EventService get(){
- return new SpringEventService();
- }
- });
- bind(EventService.class).toConstructor((Constructor<SpringEventService>)SpringEventService.class.getConstructors()[0]);
注意:第一个直接to(implemet)的方式是getProvider时new出的Provider,第二种是用Providers.of(instance)生成的ConstantProvider
注入依赖@Inject
- @Singleton
- public class MyHandler {
- @Inject
- @Named("springEventService")
- private EventService eventService;
- @Subscribe
- public void handleEvent(MyEvent event) {
- eventService.post("MyHandler",event);
- }
- }
@Inject和@Named结合使用达到按名字注入,@Inject的optional默认为false,注入时如果依赖不存在,则报错停止,当使用@Inject(optional = true)时可达到忽然依赖是否存在的效果
实例创建
- FooStarter starter = injector.getInstance(FooStarter.class);
如果injector已经有则直接返回已有对象,没有则创建一个(利用依赖注入,如果没有绑定过则不会被依赖注入),默认prototype模式(每次都新建一个),@Singleton可以指定singleton模式
getInstance的过程
先根据指定的class类new Key(),Key包括class信息和注解信息,class的hashcode和注解的hashcode决定了Key的hashcode,getProvider时是根据Key的hashcode来判断是否是同一个Key,然后取到Provider,由Provider提供最终的instance
注意:无注解时会有一个默认的hashcode
Key的hashcode计算公式
class.hashcode * 31 + annotation.hashcode
会出现多个组合得到的hashcode是相同的情况么?
2 * 31 + 3 = 65
1 * 31 + 34 = 65
为什么用这样的公式?(Java中String是如何计算hashcode的?)
Joshua Bloch's Effective Java中是这样解释的:
The value 31 was chosen because it is an odd prime. If it were even and the multiplication overflowed, information would be lost, as multiplication by 2 is equivalent to shifting. The advantage of using a prime is less clear, but it is traditional. A nice property of 31 is that the multiplication can be replaced by a shift and a subtraction for better performance: 31 * i == (i << 5) - i. Modern VMs do this sort of optimization automatically.(from Chapter 3, Item 9: Always override hashcode when you override equals, page 48)
选择值31是因为它是奇数。 如果是偶数并且乘法溢出,则信息将丢失,因为乘以2等效于移位。 使用素数的优点不太清楚,但它是传统的。 31的一个好的属性是乘法可以由移位和减法替换以获得更好的性能:31 * i ==(i << 5) - i。 现代虚拟机自动进行这种优化。(从第3章,项9:覆盖equals时始终覆盖hashcode,第48页)
参考:
http://stackoverflow.com/questions/299304/why-does-javas-hashcode-in-string-use-31-as-a-multiplier
https://www.cs.cmu.edu/~adamchik/15-121/lectures/Hashing/hashing.html
Guice对于classloader的依赖有多重要?
由于一个class被加载后是否唯一由加载的classloader决定,所以不同的classloader加载同一个class会生成两个class实例(反射中一个class也会有一个实例),两个不同的class生成的Key的hashcode则不同,所以在Guice中根据Key来获取时必须要用同一个classloader加载的类,否则获取不到,所以在OSGI方式下用Guice需要注意
injector.injectMembers(instance)
- Injector injectorBase = Guice.createInjector(new EventModule());
- Injector injector = injectorBase.createChildInjector(new SpringModule());
- MyHandler handler = new MyHandler();// eventService is null
- injector.injectMembers(handler);// eventService use instance
用一个已经有的实例,但依赖的对象为null,这时可以用injector注入依赖对象,但这个实例不会有绑定关系,所以如果其他有需要依赖这个实例的也无法注入这个实例
Injector继承
- Injector parent = Guice.createInjector(new EventModule());
- Injector child = parent .createChildInjector(new SpringModule());
child 可以依赖parent ,但反过来则不可以
依赖范围
一个Injector中如果包含了多个Module,各Module中的是可以相互使用的,也就是可以相互依赖
如果一个Injector想依赖另一个Injector中的实例,那就要通过继承了,例如功能模块想要依赖基础模块,那功能模块可以继承基础模块
依赖Tree
AOP in Guice
- Binder#bindInterceptor(Matcher<? super Class<?>> classMatcher, Matcher<? super Method> methodMatcher, org.aopalliance.intercept.MethodInterceptor... interceptors)
- bindInterceptor(Matchers.any(),Matchers.annotatedWith(Named.class),new MethodInterceptor(){
- @Override
- public Object invoke(MethodInvocation invocation) throws Throwable {
- System.out.println("do something before...");
- Object result = invocation.proceed();
- System.out.println("do something after...");
- return result;
- }
- });
Matcher通过Matchers来生成
与spring整合
如何解决这种相互依赖?
达到的效果:
处理过程:
代码:
将spring中的bean暴露给Guice:
- public class SpringModule extends AbstractModule {
- private ConfigurableListableBeanFactory beanFactory;
- public SpringModule(ConfigurableListableBeanFactory beanFactory){
- this.beanFactory = beanFactory; }
- @Override
- protected void configure() {
- bind(BeanFactory.class).toInstance(this.beanFactory);
- String[] names = this.beanFactory.getBeanDefinitionNames();
- for (String name : names) {
- try {
- Object instance = this.beanFactory.getBean(name);
- Class clazz = instance.getClass();
- bind(clazz).toInstance(instance);
- Class[] intefaces = clazz.getInterfaces();
- for (Class inteface: intefaces) {
- if (!inteface.getName().contains("com.xxxxxx")) {
- continue;
- }
- bind(inteface).annotatedWith(Names.named(name)).toInstance(instance);
- }
- bind(clazz).annotatedWith(Names.named(name)).toInstance(instance);
- } catch (Exception e) {
- }
- }
- }
- }
将Guice里的beans暴露给spring:
- @Component
- public class PbfInitProcesser implements BeanFactoryPostProcessor {
- @Override
- public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
- // map injector to spring beanFactory
- Injector spring = Guice.createInjector(new SpringModule(beanFactory));
- Injector injector = spring.createChildInjector(new ProductModule());
- PbfEnvInitUtil.shareGuiceToSpring("injector", beanFactory, injector);
- }
- }
- public class PbfEnvInitUtil {
- public static final void refresh(ApplicationContext context) {
- // refresh inject bean to autowire
- String names[] = context.getBeanDefinitionNames();
- for (String name : names) {
- context.getAutowireCapableBeanFactory().autowireBean(context.getBean(name));
- }
- }
- public static void shareGuiceToSpring(String bizName, ConfigurableListableBeanFactory beanFactory, Injector injector) {
- Map<Key<?>, Binding<?>> map = injector.getAllBindings();
- Iterator<Map.Entry<Key<?>, Binding<?>>> iterator = map.entrySet().iterator();
- while (iterator.hasNext()) {
- Map.Entry<Key<?>, Binding<?>> entry = iterator.next();
- Binding<?> binding = entry.getValue();
- Object listener = binding.getProvider().get();
- Annotation annotation = entry.getKey().getAnnotation();
- if (null != annotation && annotation instanceof Named) {
- String name = ((Named)annotation).value();
- try {
- beanFactory.registerSingleton(name, listener);
- } catch (Exception e) {
- }
- }
- }
- beanFactory.registerSingleton(bizName, injector);
- }
- }
springboot中使用:
- ApplicationContext context = SpringApplication.run(Application.class, args);
- PbfEnvInitUtil.refresh(context);