Tiny-Spring项目学习总结

Posted 2020-08-17 ShoolyShooly

人生不相见,动如参与商.

Spring基本是所有Java学习者绕不开的框架，其对于现代Java的开发具有里程碑式的作用，将java开发者从繁杂的框架和配置中解放出来（至少是部分解放出来）。在github上看到一个微型的spring框架实现项目，觉得很有必要学习一下，谁知道断断续续用了三个月才完全自己实现了一遍，本篇文章对于这个项目的学习做一个总结。

谈到Spring，我们一般会想到它的IOC和AOP特性，也就是上图的Core Containter和AOP以及Aspects部分。Tiny-Spring项目从最简单的IOC容器类开始，实现了Spring的IOC和AOP的基本功能，

先看下最基础的对于bean的定义，以下是最简单的bean定义，只包含了对于bean本身的设置和获取方法：

public class BeanDefinition {

private Object bean;

public BeanDefinition(Object bean){
    this.bean = bean;
}

public Object getBean(){
    return bean;
}

}

众所周知，Spring使用工厂方法来管理bean，那么我们还需要一个最基础的工厂类：

public class BeanFactory {

Map<String,BeanDefinition> beanDefinitionMap = new ConcurrentHashMap<>();

public Object getBean(String name){ return beanDefinitionMap.get(name).getBean();}

public void registerBeanDefinition(String name,BeanDefinition beanDefinition){
    beanDefinitionMap.put(name,beanDefinition);
}
}

这样的话我们就实现了一个最简单的bean管理功能，可以测试一下。

先定义一个pojo类：
public class HelloWorldService {

public void hello(){
    System.out.println("Hello World");
}
}

写一个测试方法：

public class BeanFactoryTest {

@Test
public void init(){

    //1.初始化BeanFactory
    BeanFactory beanFactory = new BeanFactory();

    //2.注入Bean
    BeanDefinition beanDefinition = new BeanDefinition(new HelloWorldService());
    beanFactory.registerBeanDefinition("helloWorldService",beanDefinition);

    //3.获取Bean实例
    HelloWorldService helloWorldService = (HelloWorldService)beanFactory.getBean("helloWorldService");
    helloWorldService.hello();

}
}

可以看到，我们没有直接初始化pojo类的实例，而是将其注册到bean工厂中，当需要调用的时候，再从工厂类中获取并调用。

接下来，我们需要将bean的初始化流程完全放入bean工厂中，因此需要拓展我们的BeanDefinition类：

public class BeanDefinition {

private Object bean;

private Class beanClass;

private String beanClassName;


public Object getBean() {
    return bean;
}

public void setBean(Object bean) {
    this.bean = bean;
}

public Class getBeanClass() {
    return beanClass;
}

public void setBeanClass(Class beanClass) {
    this.beanClass = beanClass;
}

public String getBeanClassName() {
    return beanClassName;
}

public void setBeanClassName(String beanClassName) {
    this.beanClassName = beanClassName;
    try{
        this.beanClass = Class.forName(beanClassName);
    }catch (ClassNotFoundException e){
        e.printStackTrace();
    }
}
}

定义bean工厂接口，只需要获取和设置bean的方法：

public interface BeanFactory {

    Object getBean(String beanName);

    void registerBeanDefinition(String beanName, BeanDefinition beanDefinition);
}

定义抽象bean工厂类，实现获取和设置bean的方法，抽象初始化bean的方法：

public abstract class AbstractBeanFactory implements BeanFactory{

private Map<String,BeanDefinition> beanDefinitionMap = new HashMap<>();

@Override
public Object getBean(String beanName) {
    return beanDefinitionMap.get(beanName).getBean();
}

@Override
public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition) {
  Object bean = doCreateBean(beanDefinition);
  beanDefinition.setBean(bean);
  beanDefinitionMap.put(beanName,beanDefinition);
}

/**
 * 创建Bean实例
 * @param beanDefinition
 * @return
 */
protected abstract Object doCreateBean(BeanDefinition beanDefinition);

}

最后，具体的bean工厂类，实现初始化bean的方法（此处通过反射初始化bean实例）：

public class AutowireCapableBeanFactory extends AbstractBeanFactory{

@Override
protected Object doCreateBean(BeanDefinition beanDefinition) {

    try {
        Object bean = beanDefinition.getBeanClass().newInstance();
        return bean;
    }catch (InstantiationException e){
        e.printStackTrace();
    }catch (IllegalAccessException e){
        e.printStackTrace();
    }

    return null;
}
}

编写对应的单元测试类；

public class BeanFactoryTest {

@Test
public void init(){

    BeanFactory beanFactory = new AutowireCapableBeanFactory();

    BeanDefinition beanDefinition = new BeanDefinition();
   // Spring使用反射来初始化bean实例，因此需要输入全限定名（涉及到动态编译的性能问题，lazy init))
    beanDefinition.setBeanClassName("com.simon.HelloWorldService");

    //将bean注册到工厂
    beanFactory.registerBeanDefinition("helloService",beanDefinition);

    HelloWorldService helloWorldService = (HelloWorldService)beanFactory.getBean("helloService");
    helloWorldService.sayHello();
}

}

下一步，如果pojo类具有属性，我们的bean工厂在初始化bean实例的时候需要能为其设置对应的属性值。

首先，拓展我们的BeanDefinition类：

public class BeanDefinition {


private Object bean;

private String beanClassName;

private Class beanClass;

private PropertyValues propertyValues;

public BeanDefinition() {
}

public Object getBean() {
    return bean;
}

public void setBean(Object bean) {
    this.bean = bean;
}

public String getBeanClassName() {
    return beanClassName;
}

public void setBeanClassName(String beanClassName) {
    this.beanClassName = beanClassName;
    try{
        this.beanClass = Class.forName(beanClassName);
    }catch(ClassNotFoundException e){
        e.printStackTrace();
    }
}

public Class getBeanClass() {
    return beanClass;
}

public void setBeanClass(Class beanClass) {
    this.beanClass = beanClass;
}

public PropertyValues getPropertyValues() {
    return propertyValues;
}

public void setPropertyValues(PropertyValues propertyValues) {
    this.propertyValues = propertyValues;
}

@Override
public String toString() {
    return "BeanDefinition{" +
            "bean=" + bean +
            ", beanClassName=\'" + beanClassName + \'\\\'\' +
            ", beanClass=" + beanClass +
            ", propertyValues=" + propertyValues +
            \'}\';
}
}

这里我们的具体工厂实现类需要修改，在初始化bean的时候将属性值设置进去：

public class AutowireCapableBeanFactory extends AbstractBeanFactory{

@Override
protected Object doCreateBean(BeanDefinition beanDefinition) throws Exception {
    Object bean = createBeanInstance(beanDefinition);
    applyPropertyValues(bean, beanDefinition);
    return bean;
}

protected Object createBeanInstance(BeanDefinition beanDefinition) throws Exception {
    return beanDefinition.getBeanClass().newInstance();
}

protected void applyPropertyValues(Object bean,BeanDefinition beanDefinition) throws Exception{
    for(PropertyValue pv:beanDefinition.getPropertyValues().getPropertyValueList()){
        Field declaredField = bean.getClass().getDeclaredField(pv.getKey());
        //使用反射绕过private限制为字段直接赋值
        declaredField.setAccessible(true);
        declaredField.set(bean,pv.getValue());

    }
}
}

对应的单元测试方法：

public class BeanFactoryTest {

@Test
public void test() throws Exception {
    // 1.初始化beanfactory
    BeanFactory beanFactory = new AutowireCapableBeanFactory();

    // 2.bean定义
    BeanDefinition beanDefinition = new BeanDefinition();
    beanDefinition.setBeanClassName("com.simon.HelloWorldService");

    // 3.设置属性
    PropertyValues propertyValues = new PropertyValues();
    propertyValues.addProperty(new PropertyValue("text", "Hello World!"));
    beanDefinition.setPropertyValues(propertyValues);

    // 4.生成bean
    beanFactory.registerBeanDefinition("helloWorldService", beanDefinition);

    // 5.获取bean
    HelloWorldService helloWorldService = (HelloWorldService) beanFactory.getBean("helloWorldService");
    helloWorldService.helloWorld();

}
}

接下来，我们要实现从配置文件读取bean的定义。

首先，定义配置文件资源定义接口：

public interface Resource {

/**
 * 通过输入流获取资源
 *
 * @return
 * @throws IOException
 */
InputStream getInputStream() throws IOException;
}

具体的资源类;

public class URLResource implements Resource{

private final URL url;

public URLResource(URL url) {
    this.url = url;
}

@Override
public InputStream getInputStream() throws IOException {

    URLConnection urlConnection = url.openConnection();
    urlConnection.connect();
    return urlConnection.getInputStream();
}
}

实现资源读取类：

public class ResourceLoader {

public Resource getResource(String location){

    URL resource = this.getClass().getClassLoader().getResource(location);
    return new URLResource(resource);
}
}

接下来我们要实现从资源中读取的BeanDefinition的功能。

首先定义读取BeanDefinition的接口：

public interface BeanDefinitionReader {

void loadBeanDefinitions(String location) throws Exception;
}

抽象的BeanDefinition读取类，含有一个资源读取类和BeanDefinition集合：

public abstract class AbstractBeanDefinitionReader implements BeanDefinitionReader{

private Map<String,BeanDefinition> registry;

private ResourceLoader resourceLoader;

public AbstractBeanDefinitionReader(ResourceLoader resourceLoader) {
    this.registry = new HashMap<String, BeanDefinition>();
    this.resourceLoader = resourceLoader;
}

public Map<String, BeanDefinition> getRegistry() {
    return registry;
}

public ResourceLoader getResourceLoader() {
    return resourceLoader;
}
}

具体的BeanDefinition读取类，从xml读取bean定义并解析，通过name-bean映射到map存储bean的信息；

public class XmlBeanDefinitionReader extends AbstractBeanDefinitionReader{

public XmlBeanDefinitionReader(ResourceLoader resourceLoader) {
    super(resourceLoader);
}

@Override
public void loadBeanDefinitions(String location) throws Exception {

    InputStream inputStream = getResourceLoader().getResource(location).getInputStream();
    doLoadBeanDefinitions(inputStream);
}

protected void doLoadBeanDefinitions(InputStream inputStream) throws Exception{

    //创建xml解析器
    DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();

    DocumentBuilder builder = factory.newDocumentBuilder();

    Document doc = builder.parse(inputStream);

    registerBeanDefinitions(doc);

    inputStream.close();
}

public void registerBeanDefinitions(Document doc){
    Element root = doc.getDocumentElement();
    parseDeanDefinitions(root);

}

protected void parseDeanDefinitions(Element root){
    NodeList nl = root.getChildNodes();
    for(int i= 0;i<nl.getLength();i++){
        Node node = nl.item(i);
        if(node instanceof Element){
            Element ele = (Element)node;
            processBeanDefinition(ele);
        }
    }
}

protected void processBeanDefinition(Element ele){
    String name = ele.getAttribute("name");
    String className = ele.getAttribute("class");

    //创建BeanDefinition对象
    BeanDefinition beanDefinition = new BeanDefinition();
    processProperty(ele,beanDefinition);
    beanDefinition.setBeanClassName(className);
    getRegistry().put(name,beanDefinition);
}

protected void processProperty(Element ele,BeanDefinition beanDefinition){
    NodeList propertyNode = ele.getElementsByTagName("property");
    for(int i=0;i<propertyNode.getLength();i++){
        Node node = propertyNode.item(i);
        if(node instanceof  Element){
           Element propertyEle = (Element)node;
           String name = propertyEle.getAttribute("name");
           String value = propertyEle.getAttribute("value");
           beanDefinition.getPropertyValues().addPropertyValue(new PropertyValue(name,value));
        }
    }
}


}

接下来定义一个bean的配置文件studyTiny.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:tx="http://www.springframework.org/schema/tx" xmlns:context="http://www.springframework.org/schema/context"
   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
http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-2.5.xsd">

<bean name="helloWorldService" class="com.simon.HelloWorldService">
    <property name="text" value="Hello World!"></property>
</bean>

</beans>

对应的单元测试类：

public class XmlBeanDefinitionReaderTest {

@Test
public void test() throws Exception {
	XmlBeanDefinitionReader xmlBeanDefinitionReader = new XmlBeanDefinitionReader(new ResourceLoader());
	xmlBeanDefinitionReader.loadBeanDefinitions("studyTiny.xml");
	Map<String, BeanDefinition> registry = xmlBeanDefinitionReader.getRegistry();
	Assert.assertTrue(registry.size() > 0);
}
}

接下来，引入我们熟悉的ApplicationContext.

定义ApplicationContext接口，继承BeanFactory，具备管理bean的能力:

public interface ApplicationContext extends BeanFactory {

}

定义抽象类，注入工厂管理bean:

public abstract class  AbstractApplicationContext implements ApplicationContext{

protected AbstractBeanFactory beanFactory;

public AbstractApplicationContext(AbstractBeanFactory abstractBeanFactory) {
    this.beanFactory = abstractBeanFactory;
}

public abstract void refresh() throws Exception;

@Override
public Object getBean(String name) throws Exception {
    return beanFactory.getBean(name);
}

}

最后实现基于xml定义bean的容器类：

public class ClassPathXmlApplicationContext extends AbstractApplicationContext{

private String configLocation;

public ClassPathXmlApplicationContext(String configLocation) throws Exception{
    this(configLocation,new AutowireCapableBeanFactory());
}

public ClassPathXmlApplicationContext(String configLocation,AbstractBeanFactory abstractBeanFactory) throws Exception{
    super(abstractBeanFactory);
    this.configLocation = configLocation;
    refresh();
}

@Override
public void refresh() throws Exception {  
   //使用xml的bean读取器获取bean的定义
    XmlBeanDefinitionReader xmlBeanDefinitionReader = new XmlBeanDefinitionReader(new ResourceLoader());
    xmlBeanDefinitionReader.loadBeanDefinitions(configLocation);
    for (Map.Entry<String, BeanDefinition> beanDefinitionEntry : xmlBeanDefinitionReader.getRegistry().entrySet()) {
        beanFactory.registerBeanDefinition(beanDefinitionEntry.getKey(), beanDefinitionEntry.getValue());
    }
}
}

单元测试类；

public class ApplicationContextTest {

@Test
public void test() throws Exception{
    ApplicationContext applicationContext = new ClassPathXmlApplicationContext("studyTiny.xml");

    HelloWorldService helloWorldService = (HelloWorldService)applicationContext.getBean("helloWorldService");

    helloWorldService.helloWorld();
}
}

接下来我们来实现AOP功能，AOP有Pointcut（切入点）, Advice（功能增强）以及织入weave，当然我们还需要将AOP整合到Spring的生命周期中。

首先定义被代理对象：

public class TargetSource {

private Class targetClass;

private Object target;

public TargetSource(Class<?> targetClass, Object target) {
    this.targetClass = targetClass;
    this.target = target;
}

public Class getTargetClass() {
    return targetClass;
}

public Object getTarget() {
    return target;
}
}

代理相关的元数据类：

public class AdvisedSupport {

private TargetSource targetSource;

private MethodInterceptor methodInterceptor;

public TargetSource getTargetSource() {
    return targetSource;
}

public void setTargetSource(TargetSource targetSource) {
    this.targetSource = targetSource;
}

public MethodInterceptor getMethodInterceptor() {
    return methodInterceptor;
}

public void setMethodInterceptor(MethodInterceptor methodInterceptor) {
    this.methodInterceptor = methodInterceptor;
}
}

切入点对象；

public class ReflectiveMethodInvocation implements MethodInvocation {

/** 被代理类 */
private Object target;

/** 被代理的方法 */
private Method method;

/** 方法入参 */
private Object[] args;

public ReflectiveMethodInvocation(Object target, Method method, Object[] args) {
    this.target = target;
    this.method = method;
    this.args = args;
}

@Override
public Method getMethod() {
    return method;
}

@Override
public Object[] getArguments() {
    return args;
}

/**
 * 调用被代理方法
 * @return
 * @throws Throwable
 */
@Override
public Object proceed() throws Throwable {
    return method.invoke(target,args);
}

@Override
public Object getThis() {
    return target;
}

/**
 * 获取被调用方法
 * @return
 */
@Override
public AccessibleObject getStaticPart() {
    return method;
}
}

代理接口：

public interface AopProxy {

Object getProxy();
}

JDK代理类：

public class JdkDynamicAopProxy implements AopProxy, InvocationHandler {

private AdvisedSupport advisedSupport;

public JdkDynamicAopProxy(AdvisedSupport advisedSupport) {
    this.advisedSupport = advisedSupport;
}

/**
 * 使用jdk的动态代理获取代理对象
 * @return
 */
@Override
public Object getProxy() {
    return Proxy.newProxyInstance(getClass().getClassLoader(),new Class[]{
        advisedSupport.getTargetSource().getTargetClass()
    },this);
}

@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    MethodInterceptor methodInterceptor = advisedSupport.getMethodInterceptor();

    return methodInterceptor.invoke(new ReflectiveMethodInvocation(advisedSupport.getTargetSource().getTarget(),method,args));
}
}

接下来可以测试了，先定义一个拦截器类：

public class TimerInterceptor implements MethodInterceptor {

@Override
public Object invoke(MethodInvocation invocation) throws Throwable {

    long time = System.nanoTime();

    System.out.println("Invocation of Method "+invocation.getMethod().getName()+" start!");

    Object proceed = invocation.proceed();

    System.out.println("Invocation of Method "+invocation.getMethod().getName()+" ends! takes "+(System.nanoTime() - time ));

    return proceed;
}
}

接下来写单元测试类：

public class JdkDynamicAopProxyTest {

@Test
public void test() throws Exception{

    //init context
    ApplicationContext applicationContext = new ClassPathXmlApplicationContext("studyTiny.xml");

    //helloWorldService without aop
    HelloWorldService helloWorldService = (HelloWorldService)applicationContext.getBean("helloWorldService");
    helloWorldService.helloWorld();;

    //helloWorldService with aop
    AdvisedSupport advisedSupport = new AdvisedSupport();
    TargetSource targetSource = new TargetSource(HelloWorldService.class,helloWorldService);
    advisedSupport.setTargetSource(targetSource);

    //set interceptor
    TimerInterceptor timerInterceptor = new TimerInterceptor();
    advisedSupport.setMethodInterceptor(timerInterceptor);

    //set proxy
    JdkDynamicAopProxy jdkDynamicAopProxy = new JdkDynamicAopProxy(advisedSupport);
    HelloWorldService helloWorldProxy = (HelloWorldService)jdkDynamicAopProxy.getProxy();

    helloWorldProxy.helloWorld();
}
}