Spring boot實現一個簡單的ioc(2)。本站提示廣大學習愛好者:(Spring boot實現一個簡單的ioc(2))文章只能為提供參考,不一定能成為您想要的結果。以下是Spring boot實現一個簡單的ioc(2)正文
前言
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仿照spring-boot的項目結構以及部分注解,寫一個簡單的ioc容器。
測試代碼完成後,便正式開始這個ioc容器的開發工作。
正文
項目結構
實際上三四個類完全能搞定這個簡單的ioc容器,但是出於可擴展性的考慮,還是寫了不少的類。
因篇幅限制,接下來只將幾個最重要的類的代碼貼出來並加以說明,完整的代碼請直接參考https://github.com/clayandgithub/simple-ioc。
SimpleAutowired
代碼
import java.lang.annotation.*; @Target({ElementType.FIELD}) @Retention(RetentionPolicy.RUNTIME) @Documented public @interface SimpleAutowired { boolean required() default true; String value() default ""; // this field is moved from @Qualifier to here for simplicity }
說明
@SimpleAutowired的作用是用於注解需要自動裝配的字段。
此類和spring的@Autowired的作用類似。但又有以下兩個區別:
- @SimpleAutowired只能作用於類字段,而不能作用於方法(這樣實現起來相對簡單些,不會用到aop)
- @SimpleAutowired中包括了required(是否一定需要裝配)和value(要裝配的bean的名字)兩個字段,實際上是將spring中的@Autowired以及Qualifier的功能簡單地融合到了一起
SimpleBean
代碼
import java.lang.annotation.*; @Target({ElementType.METHOD, ElementType.ANNOTATION_TYPE}) @Retention(RetentionPolicy.RUNTIME) @Documented public @interface SimpleBean { String value() default ""; }
說明
@SimpleBean作用於方法,根據方法返回值來生成一個bean,對應spring中的@Bean
用value來設置要生成的bean的名字
SimpleComponent
代碼
import java.lang.annotation.*; @Target({ElementType.METHOD, ElementType.ANNOTATION_TYPE}) @Retention(RetentionPolicy.RUNTIME) @Documented public @interface SimpleBean { String value() default ""; }
說明
@SimpleComponent作用於類,ioc容器會為每一個擁有@SimpleComponent的類生成一個bean,對應spring中的@Component。特殊說明,為了簡單起見,@SimpleComponent注解的類必須擁有一個無參構造函數,否則無法生成該類的實例,這個在之後的SimpleAppliationContext中的processSingleClass方法中會有說明。
SimpleIocBootApplication
代碼
import java.lang.annotation.*; @Target({ElementType.TYPE}) @Retention(RetentionPolicy.RUNTIME) @Documented public @interface SimpleIocBootApplication { String[] basePackages() default {}; }
說明
@SimpleIocBootApplication作用於應用的入口類。
這個啟動模式是照搬了spring-boot的啟動模式,將啟動任務委托給SimpleIocApplication來完成。ioc容器將根據注解@SimpleIocBootApplication的相關配置自動掃描相應的package,生成beans並完成自動裝配。(如果沒有配置,默認掃描入口類(測試程序中的SampleApplication)所在的package及其子package)
以上就是這個ioc容器所提供的所有注解,接下來講解ioc容器的掃描和裝配過程的實現。
SimpleIocApplication
代碼
import com.clayoverwind.simpleioc.context.*; import com.clayoverwind.simpleioc.util.LogUtil; import java.util.Arrays; import java.util.Map; import java.util.logging.Logger; public class SimpleIocApplication { private Class<?> applicationEntryClass; private ApplicationContext applicationContext; private final Logger LOGGER = LogUtil.getLogger(this.getClass()); public SimpleIocApplication(Class<?> applicationEntryClass) { this.applicationEntryClass = applicationEntryClass; } public static void run(Class<?> applicationEntryClass, String[] args) { new SimpleIocApplication(applicationEntryClass).run(args); } public void run(String[] args) { LOGGER.info("start running......"); // create application context and application initializer applicationContext = createSimpleApplicationContext(); ApplicationContextInitializer initializer = createSimpleApplicationContextInitializer(applicationEntryClass); // initialize the application context (this is where we create beans) initializer.initialize(applicationContext); // here maybe exist a hidden cast // process those special beans processSpecialBeans(args); LOGGER.info("over!"); } private SimpleApplicationContextInitializer createSimpleApplicationContextInitializer(Class<?> entryClass) { // get base packages SimpleIocBootApplication annotation = entryClass.getDeclaredAnnotation(SimpleIocBootApplication.class); String[] basePackages = annotation.basePackages(); if (basePackages.length == 0) { basePackages = new String[]{entryClass.getPackage().getName()}; } // create context initializer with base packages return new SimpleApplicationContextInitializer(Arrays.asList(basePackages)); } private SimpleApplicationContext createSimpleApplicationContext() { return new SimpleApplicationContext(); } private void processSpecialBeans(String[] args) { callRegisteredRunners(args); } private void callRegisteredRunners(String[] args) { Map<String, SimpleIocApplicationRunner> applicationRunners = applicationContext.getBeansOfType(SimpleIocApplicationRunner.class); try { for (SimpleIocApplicationRunner applicationRunner : applicationRunners.values()) { applicationRunner.run(args); } } catch (Exception e) { throw new RuntimeException(e); } } }
說明
前面說到應用的啟動會委托SimpleIocApplication來完成,通過將應用入口類(測試程序中的SampleApplication)傳入SimpleIocApplication的構造函數,構造出SimpleIocApplication的一個實例並運行run方法。在run方法中,會首先生成一個applicationContext,並調用SimpleApplicationContextInitializer來完成applicationContext的初始化(bean的掃描、裝配)。然後調用processSpecialBeans來處理一些特殊的bean,如實現了SimpleIocApplicationRunner接口的bean會調用run方法來完成一些應用程序的啟動任務。
這就是這個ioc容器的整個流程。
SimpleApplicationContextInitializer
代碼
import java.io.IOException; import java.util.LinkedHashSet; import java.util.List; import java.util.Set; public class SimpleApplicationContextInitializer implements ApplicationContextInitializer<SimpleApplicationContext> { private Set<String> basePackages = new LinkedHashSet<>(); public SimpleApplicationContextInitializer(List<String> basePackages) { this.basePackages.addAll(basePackages); } @Override public void initialize(SimpleApplicationContext applicationContext) { try { applicationContext.scan(basePackages, true); } catch (ClassNotFoundException e) { throw new RuntimeException(e); } catch (IOException e) { throw new RuntimeException(e); } applicationContext.setStartupDate(System.currentTimeMillis()); } }
說明
在SimpleIocApplication的run中,會根據basePackages來構造一個SimpleApplicationContextInitializer 的實例,進而通過這個ApplicationContextInitializer來完成SimpleApplicationContext 的初始化。
在SimpleApplicationContextInitializer中, 簡單地調用SimpleApplicationContext 中的scan即可完成SimpleApplicationContext的初始化任務
SimpleApplicationContext
說明:
終於到了最重要的部分了,在SimpleApplicationContext中將真正完成掃描、生成bean以及自動裝配的任務。這裡scan即為SimpleApplicationContext的程序入口,由SimpleApplicationContextInitializer在初始化時調用。
代碼的調用邏輯簡單易懂,就不多加說明了。
這裡只簡單列一下各個字段的含義以及幾個比較關鍵的方法的作用。
字段
- startupDate:啟動時間記錄字段
- scannedPackages:已經掃描的包的集合,保證不重復掃描
- registeredBeans:已經完全裝配好並注冊好了的bean
- earlyBeans : 只是生成好了,還未裝配完成的bean,用於處理循環依賴的問題
- totalBeanCount : 所有bean的計數器,在生成bean的名字時會用到其唯一性
方法
- processEarlyBeans:用於最終裝配earlyBeans 中的bean,若裝配成功,則將bean移至registeredBeans,否則報錯
- scan : 掃描並處理傳入的package集合
- processSingleClass:處理單個類,嘗試生成該類的bean並進行裝配(前提是此類有@SimpleComponent注解)
- createBeansByMethodsOfClass : 顧名思義,根據那些被@Bean注解的方法來生成bean
- autowireFields:嘗試裝配某個bean,lastChance代表是否在裝配失敗是報錯(在第一次裝配時,此值為false,在裝配失敗後會將bean移至earlyBeans,在第二次裝配時,此值為true,實際上就是在裝配earlyBeans中的bean,因此若仍然裝配失敗,就會報錯)。在這個方法中,裝配相應的bean時會從registeredBeans以及earlyBeans中去尋找符合條件的bean,只要找到,不管是來自哪裡,都算裝配成功。
代碼
import com.clayoverwind.simpleioc.context.annotation.SimpleAutowired; import com.clayoverwind.simpleioc.context.annotation.SimpleBean; import com.clayoverwind.simpleioc.context.annotation.SimpleComponent; import com.clayoverwind.simpleioc.context.factory.Bean; import com.clayoverwind.simpleioc.util.ClassUtil; import com.clayoverwind.simpleioc.util.ConcurrentHashSet; import com.clayoverwind.simpleioc.util.LogUtil; import java.io.IOException; import java.lang.annotation.Annotation; import java.lang.reflect.Field; import java.lang.reflect.InvocationTargetException; import java.lang.reflect.Method; import java.util.*; import java.util.concurrent.ConcurrentHashMap; import java.util.concurrent.atomic.AtomicLong; import java.util.logging.Logger; /** * @author clayoverwind * @E-mail [email protected] * @version 2017/4/5 */ public class SimpleApplicationContext implements ApplicationContext { private long startupDate; private Set<String> scannedPackages = new ConcurrentHashSet<>(); private Map<String, Bean> registeredBeans = new ConcurrentHashMap<>(); private Map<String, Bean> earlyBeans = new ConcurrentHashMap<>(); private final Logger LOGGER = LogUtil.getLogger(this.getClass()); AtomicLong totalBeanCount = new AtomicLong(0L); AtomicLong nameConflictCount = new AtomicLong(0L); @Override public Object getBean(String name) { return registeredBeans.get(name); } @Override public <T> T getBean(String name, Class<T> type) { Bean bean = (Bean)getBean(name); return bean == null ? null : (type.isAssignableFrom(bean.getClazz()) ? type.cast(bean.getObject()) : null); } @Override public <T> T getBean(Class<T> type) { Map<String, T> map = getBeansOfType(type); return map.isEmpty() ? null : type.cast(map.values().toArray()[0]); } @Override public boolean containsBean(String name) { return getBean(name) != null; } @Override public <T> Map<String, T> getBeansOfType(Class<T> type) { Map<String, T> res = new HashMap<>(); registeredBeans.entrySet().stream().filter(entry -> type.isAssignableFrom(entry.getValue().getClazz())).forEach(entry -> res.put(entry.getKey(), type.cast(entry.getValue().getObject()))); return res; } @Override public void setStartupDate(long startupDate) { this.startupDate = startupDate; } @Override public long getStartupDate() { return startupDate; } /** * try to autowire those beans in earlyBeans * if succeed, remove it from earlyBeans and put it into registeredBeans * otherwise ,throw a RuntimeException(in autowireFields) */ private synchronized void processEarlyBeans() { for (Map.Entry<String, Bean> entry : earlyBeans.entrySet()) { Bean myBean = entry.getValue(); try { if (autowireFields(myBean.getObject(), myBean.getClazz(), true)) { registeredBeans.put(entry.getKey(), myBean); earlyBeans.remove(entry.getKey()); } } catch (IllegalAccessException e) { throw new RuntimeException(e); } } } /** * scan base packages and create beans * @param basePackages * @param recursively * @throws ClassNotFoundException */ public void scan(Set<String> basePackages, boolean recursively) throws ClassNotFoundException, IOException { LOGGER.info("start scanning......"); ClassLoader classLoader = Thread.currentThread().getContextClassLoader(); // get all classes who haven't been registered Set<Class<?>> classes = new LinkedHashSet<>(); for (String packageName : basePackages) { if (scannedPackages.add(packageName)) { classes.addAll(ClassUtil.getClassesByPackageName(classLoader, packageName, recursively)); } } // autowire or create bean for each class classes.forEach(this::processSingleClass); processEarlyBeans(); LOGGER.info("scan over!"); } /** * try to create a bean for certain class, put it into registeredBeans if success, otherwise put it into earlyBeans * @param clazz */ private void processSingleClass(Class<?> clazz) { LOGGER.info(String.format("processSingleClass [%s] ...", clazz.getName())); Annotation[] annotations = clazz.getDeclaredAnnotations(); for (Annotation annotation : annotations) { if (annotation instanceof SimpleComponent) { Object instance; try { instance = clazz.newInstance(); } catch (InstantiationException e) { throw new RuntimeException(e); } catch (IllegalAccessException e) { throw new RuntimeException(e); } long beanId = totalBeanCount.getAndIncrement(); SimpleComponent component = (SimpleComponent) annotation; String beanName = component.value(); if (beanName.isEmpty()) { beanName = getUniqueBeanNameByClassAndBeanId(clazz, beanId); } try { if (autowireFields(instance, clazz, false)) { registeredBeans.put(beanName, new Bean(instance, clazz)); } else { earlyBeans.put(beanName, new Bean(instance, clazz)); } } catch (IllegalAccessException e) { throw new RuntimeException(e); } try { createBeansByMethodsOfClass(instance, clazz); } catch (InvocationTargetException e) { throw new RuntimeException(e); } catch (IllegalAccessException e) { throw new RuntimeException(e); } } } } private void createBeansByMethodsOfClass(Object instance, Class<?> clazz) throws InvocationTargetException, IllegalAccessException { List<Method> methods = getMethodsWithAnnotation(clazz, SimpleBean.class); for (Method method : methods) { method.setAccessible(true); Object methodBean = method.invoke(instance); long beanId = totalBeanCount.getAndIncrement(); Class<?> methodBeanClass = methodBean.getClass(); //bean name SimpleBean simpleBean = method.getAnnotation(SimpleBean.class); String beanName = simpleBean.value(); if (beanName.isEmpty()) { beanName = getUniqueBeanNameByClassAndBeanId(clazz, beanId); } // register bean registeredBeans.put(beanName, new Bean(methodBean, methodBeanClass)); } } private List<Method> getMethodsWithAnnotation(Class<?> clazz, Class<?> annotationClass) { List<Method> res = new LinkedList<>(); Method[] methods = clazz.getDeclaredMethods(); for (Method method : methods) { Annotation[] annotations = method.getAnnotations(); for (Annotation annotation : annotations) { if (annotation.annotationType() == annotationClass) { res.add(method); break; } } } return res; } /** * try autowire all fields of a certain instance * @param instance * @param clazz * @param lastChance * @return true if success, otherwise return false or throw a exception if this is the lastChance * @throws IllegalAccessException */ private boolean autowireFields(Object instance, Class<?> clazz, boolean lastChance) throws IllegalAccessException { Field[] fields = clazz.getDeclaredFields(); for (Field field : fields) { Annotation[] annotations = field.getAnnotations(); for (Annotation annotation : annotations) { if (annotation instanceof SimpleAutowired) { SimpleAutowired autowired = (SimpleAutowired) annotation; String beanName = autowired.value(); Bean bean = getSimpleBeanByNameOrType(beanName, field.getType(), true); if (bean == null) { if (lastChance) { if (!autowired.required()) { break; } throw new RuntimeException(String.format("Failed in autowireFields : [%s].[%s]", clazz.getName(), field.getName())); } else { return false; } } field.setAccessible(true); field.set(instance, bean.getObject()); } } } return true; } /** * only used in autowireFields * @param beanName * @param type * @param allowEarlyBean * @return */ private Bean getSimpleBeanByNameOrType(String beanName, Class<?> type, boolean allowEarlyBean) { // 1. by name Bean res = registeredBeans.get(beanName); if (res == null && allowEarlyBean) { res = earlyBeans.get(beanName); } // 2. by type if (type != null) { if (res == null) { res = getSimpleBeanByType(type, registeredBeans); } if (res == null && allowEarlyBean) { res = getSimpleBeanByType(type, earlyBeans); } } return res; } /** * search bean by type in certain beans map * @param type * @param beansMap * @return */ private Bean getSimpleBeanByType(Class<?> type, Map<String, Bean> beansMap) { List<Bean> beans = new LinkedList<>(); beansMap.entrySet().stream().filter(entry -> type.isAssignableFrom(entry.getValue().getClazz())).forEach(entry -> beans.add(entry.getValue())); if (beans.size() > 1) { throw new RuntimeException(String.format("Autowire by type, but more than one instance of type [%s] is founded!", beans.get(0).getClazz().getName())); } return beans.isEmpty() ? null : beans.get(0); } private String getUniqueBeanNameByClassAndBeanId(Class<?> clazz, long beanId) { String beanName = clazz.getName() + "_" + beanId; while (registeredBeans.containsKey(beanName) || earlyBeans.containsKey(beanName)) { beanName = clazz.getName() + "_" + beanId + "_" + nameConflictCount.getAndIncrement(); } return beanName; } }
後記
至此,一個簡單的ioc容器就完成了,總結一下優缺點。
優點:
小而簡單。
可以使用@SimpleBean、@SimpleComponent以及@SimpleAutowired 來完成一些簡單但常用的依賴注入任務.
缺點:
很明顯,實現過於簡單,提供的功能太少。
如果你想了解ioc的實現原理,或者你想要開發一個小型個人項目但又嫌spring過於龐大,這個簡單的ioc容器或許可以幫到你。
如果你想做的不僅如此,那麼你應該將目光轉向spring-boot。
完整代碼參考:https://github.com/clayandgithub/simple-ioc。
以上就是本文的全部內容,希望對大家的學習有所幫助,也希望大家多多支持。