前言
为了巩固学习Spring框架，我尝试通过手写spring，实现SpringMVC基本功能来学习Spring源码。
实现功能
这次先写了一个简易的框架，实现了最基本的IoC功能，以及springmvc中常用的注解，具体如下:
@Controller@RequestMapping@RequestParam@Autowired@Bean
代码
内嵌服务器
采用了apache的embed-core包在项目中内置了一个tomcat服务器，直接调用一个自己写的start()方法即可启动。本包在gradle中依赖如下：
// https://mvnrepository.com/artifact/org.apache.tomcat.embed/tomcat-embed-corecompile
group: 'org.apache.tomcat.embed', name: 'tomcat-embed-core', version: '8.5.23'
下面是TomcatServer类：
/**
* Created by makersy on 2019
*/
public class TomcatServer {
private Tomcat tomcat;
private String[] args;
public TomcatServer(String[] args) {
this.args = args;
}
//启动类
public void startTomcat() throws LifecycleException {
tomcat = new Tomcat();
tomcat.setPort(6699);
tomcat.start();
Context context = new StandardContext();
context.setPath("");
context.addLifecycleListener(new Tomcat.FixContextListener()); //默认监听器
DispatcherServlet servlet = new DispatcherServlet(); //前端控制器
Tomcat.addServlet(context, "dispatcherServlet", servlet).setAsyncSupported(true); //支持异步的servlet
context.addServletMappingDecoded("/", "dispatcherServlet"); //为Servlet绑定映射，/表示可以处理所有uri
tomcat.getHost().addChild(context);
Thread awaitThread = new Thread("tomcat_await_thread"){
@Override
public void run() {
TomcatServer.this.tomcat.getServer().await(); //声明该线程一直在等待
}
};
//设置为非守护线程
awaitThread.setDaemon(false);
//使该线程等待
awaitThread.start();
}
}
DispatcherServlet（用来维护Servlet）
DispatcherServlet类进行servlet的维护，实现请求分发。
/**
* Created by makersy on 2019
*/
public class DispatcherServlet implements Servlet {
@Override
public void init(ServletConfig config) throws ServletException {
}
@Override
public ServletConfig getServletConfig() {
return null;
}
@Override
public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException {
for (MappingHandler mappingHandler : HandlerManager.mappingHandlerList) {
try {
if (mappingHandler.handle(req, res)) {
return;
}
} catch (IllegalAccessException | InstantiationException | InvocationTargetException e) {
e.printStackTrace();
}
}
}
@Override
public String getServletInfo() {
return null;
}
@Override
public void destroy() {
}
}
MappingHandler
MappingHandler用来处理经过dispatcherservlet的请求uri，每个MappingHandler处理其匹配的uri请求。
/**
* Created by makersy on 2019
*/
public class MappingHandler {
private String uri;
private Method method;
private Class<?> controller;
private String[] args;
public boolean handle(ServletRequest request, ServletResponse response) throws IllegalAccessException, InstantiationException, InvocationTargetException, IOException {
String requestUri = ((HttpServletRequest)request).getRequestURI();
if (!uri.equals(requestUri)) {
return false;
}
Object[] parameters = new Object[args.length];
for (int i = 0; i < args.length; i++) {
parameters[i] = request.getParameter(args[i]);
}
Object ctl = BeanFactory.getBean(controller);
Object res = method.invoke(ctl, parameters);
response.getWriter().println(res.toString());
return true;
}
public MappingHandler(String uri, Method method, Class<?> controller, String[] args) {
this.uri = uri;
this.method = method;
this.controller = controller;
this.args = args;
}
}
HandlerManager
HandlerManager负责处理controller注解，将其转换为handler。
/**
* Created by makersy on 2019
*/
public class HandlerManager {
public static List<MappingHandler> mappingHandlerList = new ArrayList<>();
/**
* 将list中的controller转化为MappingHandler
* @param classList 类列表
*/
public static void resolveMappingHandler(List<Class<?>> classList) {
for (Class<?> cls : classList) {
if (cls.isAnnotationPresent(Controller.class)) {
parseHandlerFromController(cls);
}
}
}
/**
* 将controller转化为handler
* @param cls
*/
private static void parseHandlerFromController(Class<?> cls) {
Method[] methods = cls.getDeclaredMethods();
for (Method method : methods) {
//判断方法是否有RequestMapping注解
if (!method.isAnnotationPresent(RequestMapping.class)) {
continue;
}
String uri = method.getDeclaredAnnotation(RequestMapping.class).value();
List<String> paramNameList = new ArrayList<>();
//获取method的带有RequestParam注解的参数，形成一个list
for (Parameter parameter : method.getParameters()) {
if (parameter.isAnnotationPresent(RequestParam.class)) {
paramNameList.add(parameter.getDeclaredAnnotation(RequestParam.class).value());
}
}
String[] params = paramNameList.toArray(new String[paramNameList.size()]);
MappingHandler mappingHandler = new MappingHandler(uri, method, cls, params);
HandlerManager.mappingHandlerList.add(mappingHandler);
}
}
}
ClassScanner
负责扫描一个jar包下面的所有类。用于初始化时获取所有类的列表，从而进行依赖注入，以及controller扫描。
/**
* Created by makersy on 2019
*/
public class ClassScanner {
/**
* 扫描一个包下面的所有类
* @param packageName 包名
* @return
* @throws IOException
* @throws ClassNotFoundException
*/
public static List<Class<?>> scanClass(String packageName) throws IOException, ClassNotFoundException {
List<Class<?>> classList = new ArrayList<>();
String path = packageName.replace(".", "/"); //将包名转化为路径名
ClassLoader classLoader = Thread.currentThread().getContextClassLoader(); //获取类加载器
Enumeration<URL> resources = classLoader.getResources(path);
while (resources.hasMoreElements()) {
URL resource = resources.nextElement();
if (resource.getProtocol().contains("jar")) {
//如果资源类型是jar包
JarURLConnection jarURLConnection = (JarURLConnection) resource.openConnection();
String jarFilePath = jarURLConnection.getJarFile().getName();
classList.addAll(getClassesFromJar(jarFilePath, path));
} else {
//todo
}
}
return classList;
}
/**
* 获取一个jar包下所有类
* @param jarFilePath
* @param path
* @return 类的list
* @throws IOException
* @throws ClassNotFoundException
*/
private static List<Class<?>> getClassesFromJar(String jarFilePath, String path) throws IOException, ClassNotFoundException {
List<Class<?>> classes = new ArrayList<>();
JarFile jarFile = new JarFile(jarFilePath);
Enumeration<JarEntry> jarEntries = jarFile.entries();
while (jarEntries.hasMoreElements()) {
JarEntry jarEntry = jarEntries.nextElement();
String entryName = jarEntry.getName();
if (entryName.startsWith(path) && entryName.endsWith(".class")) {
String classFullName = entryName.replace("/", ".").substring(0, entryName.length() - 6); //类的全限定名
classes.add(Class.forName(classFullName));
}
}
return classes;
}
}
Controller、RequestMapping和RequestParam注解
关于注解，可以参考我之前的文章：Java的注解
Controller
/**
* Created by makersy on 2019
*/
@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
public @interface Controller {
}
RequestMapping
/**
* Created by makersy on 2019
*/
@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface RequestMapping {
String value();
}
RequestParam
/**
* Created by makersy on 2019
*/
@Documented
@Retention(RetentionPolicy.RUNTIME) //保存级别
@Trget(ElementType.PARAMETER)
public @interface RequestParam {
String value();
}
BeanFactory
这个是IoC的重点部分，所有的依赖都是由BeanFactory处理并注入的。
package top.makersy.beans;
import top.makersy.web.mvc.Controller;
import java.lang.reflect.Field;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
/**
* Created by makersy on 2019
*/
public class BeanFactory {
//用一个类和实例的映射来模拟Bean工厂
private static Map<Class<?>, Object> classToBean = new ConcurrentHashMap<>();
//从映射中获取Bean
public static Object getBean(Class<?> cls){
return classToBean.get(cls);
}
/**
* Bean初始化，将表中所有类的依赖都加入 classToBean 这个映射中
* @param classList 包中所有类的集合
* @throws Exception
*/
public static void initBean(List<Class<?>> classList) throws Exception {
List<Class<?>> toCreate = new ArrayList<>(classList); //新建1个list来存放，以免改变了传入List的值
//一一初始化每一个类直到将类集合全部初始化完为止
while (toCreate.size() != 0) {
int remainSize = toCreate.size();
for (int i = 0; i < toCreate.size(); i++) {
if (finishCreate(toCreate.get(i))) {
toCreate.remove(i);
}
}
// 当要创建的Bean列表长度始终不变时，说明出现了Bean之间相互依赖的问题。
// 因为我们采取的策略是当前Bean创建失败就去创建下一个，这样后面的创建完了有来重新创建前
// 面的依赖，如果这个阶段了list长度始终不变，那么说明Bean之间存在相互的依赖，A不创建B没
// 法创建，B不创建A也没法创建。
// 这里不进行处理，而是直接抛出异常
if (toCreate.size() == remainSize) {
throw new Exception("cycle dependency!");
}
}
}
private static boolean finishCreate(Class<?> cls) throws IllegalAccessException, InstantiationException {
if (!cls.isAnnotationPresent(Bean.class) && !cls.isAnnotationPresent(Controller.class)) {
return true;
}
Object bean = cls.newInstance();
//获取所有字段，处理其中需要自动注入的
for (Field field : cls.getDeclaredFields()) {
//处理 autowired 注解，自动注入
if (field.isAnnotationPresent(Autowired.class)) {
Class<?> fieldType = field.getType();
Object relianBean = BeanFactory.getBean(fieldType); //从BeanFactory中获取依赖的Bean
//注意这里在BeanFactory中没有找到依赖的Bean时就返回false，放弃创建当前Bean，转而创建后面的。
if (relianBean == null) {
return false;
}
field.setAccessible(true); //关闭安全检查
field.set(bean, relianBean); //将bean的field值更新为relianBean，field值即需要注入的依赖
}
}
classToBean.put(cls, bean);
return true;
}
}
Autowired、Bean注解
Autowired
/**
* Created by makersy on 2019
*/
@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
public @interface Autowired {
}
Bean
/**
* Created by makersy on 2019
*/
@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
public @interface Bean {
}
最后
因为是刚开始，所以只实现了一些基础功能，ioc的循环依赖处理、aop都还没有实现，后面我会在此基础上进行完善。
原创文章，作者：奋斗，如若转载，请注明出处：https://blog.ytso.com/tech/pnotes/19358.html