偶然看到一篇100多行实现SpringMvc的博客，阅读后整理加实现出来。大家共勉！（纸上得来终觉浅，绝知此事要躬行。）
实现Spring的部分。
代码解析如下：
1、首先创建Servelt，继承HttpServlet。覆盖init/doGet/doPost方法。
@Override
public void init() throws ServletException {
try {
// 初始化配置文件
initConfig(super.getServletConfig().getInitParameter(CONFIG_NAME));
// 扫描类
doScanPackage(configProperties.getProperty("packageScan"));
// 加载类
initBeanInitializing();
// 依赖注入
initBeanAutowired();
// 路径映射
initServletDispatch();
} catch (Exception e) {
e.printStackTrace();
}
System.out.println("====>beanFactory:\n"+beanFactory);
System.out.println("====>requestMap:\n"+requestMap);
}
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException{
this.doPost(req, resp);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException{
doDispatch(req,resp);
}
2、配置web.xml
<servlet> <servlet-name>cwDispatchServlet</servlet-name> <servlet-class>com.cw.servlets.CWDispatchServlet</servlet-class> <init-param> <param-name>dispatchConfig</param-name> <param-value>config.properties</param-value> </init-param> <load-on-startup>1</load-on-startup> </servlet> <servlet-mapping> <servlet-name>cwDispatchServlet</servlet-name> <url-pattern>*.htm</url-pattern> </servlet-mapping>
2.1、配置文件config.properties在根目录，如下
# 设置配置文件 packageScan=com.cw.demo
3、定义支持的注入，如
Autowired
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
@Inherited
public @interface CWAutowired {
String value() default "";
}
Controller
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@Inherited
public @interface CWController {
String value() default "";
}
RequestMapping
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE,ElementType.METHOD})
@Inherited
public @interface CWRequestMapping {
String value() default "";
}
Service
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@Inherited
public @interface CWService {
String value() default "";
}
4、在Servlet的init方法中，依次实现
4.1、加载配置文件
private void initConfig(String configName){
InputStream inputStream = null;
try {
System.out.println("------->configName:"+configName);
inputStream = this.getClass().getClassLoader().getResourceAsStream(configName);
configProperties.load(inputStream);
} catch (Exception e) {
e.printStackTrace();
}finally {
if(null != inputStream) {
try {
inputStream.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
4.1、扫描所有Java类
/**
* 扫描类
* @Title: doScanPackage
* @param packagePath
* @return void
*/
private void doScanPackage(String packagePath) {
System.out.println("path:"+packagePath.replaceAll("\\.", "/"));
URL url = this.getClass().getClassLoader().getResource("/"+packagePath.replaceAll("\\.", "/"));
File file = new File(url.getFile());
for(File sub:file.listFiles()) {
if(sub.isDirectory()) {
doScanPackage(packagePath+"."+sub.getName());
}else {
String clsName = packagePath+"."+sub.getName().replace(".class","");
this.clsList.add(clsName);
}
}
}
4.3、初始化类
private void initBeanInitializing() throws ClassNotFoundException, InstantiationException, IllegalAccessException {
for(String clsName:clsList) {
Class cls = Class.forName(clsName);
if(cls.isAnnotationPresent(CWController.class)) {
String name = cls.getSimpleName();
beanFactory.put(lowerFirstChar(name) , cls.newInstance());
}else if(cls.isAnnotationPresent(CWService.class)) {
CWService service = (CWService) cls.getAnnotation(CWService.class);
String defaultName = service.value();
if(!"".equals(defaultName)) {
beanFactory.put(defaultName, cls.newInstance());
}else {
Class[] interfaces = cls.getInterfaces();
Object instance = cls.newInstance();
for(Class inter:interfaces) {
beanFactory.put(lowerFirstChar(inter.getSimpleName()), instance);
}
}
}else if(cls.isAnnotationPresent(CWComponent.class)){
String name = cls.getName();
beanFactory.put(lowerFirstChar(name), cls.newInstance());
}
}
}
4.4、完成类的依赖注入
private void initBeanAutowired() throws IllegalArgumentException, IllegalAccessException {
for(Map.Entry<String, Object> entry:beanFactory.entrySet()) {
Object bean = entry.getValue();
Field[] fields = bean.getClass().getDeclaredFields();
if(null == fields || fields.length ==0 ) {
continue;
}
for(Field field:fields) {
if(field.isAnnotationPresent(CWAutowired.class)) {
String fieldTypeName = field.getType().getSimpleName();
field.setAccessible(true);
field.set(bean, beanFactory.get(this.lowerFirstChar(fieldTypeName)));
}
}
}
}
4.5、完成request的路径映射
private void initServletDispatch() {
for(Map.Entry<String, Object> entry:beanFactory.entrySet()) {
Object bean = entry.getValue();
System.out.println(entry.getKey()+":"+entry.getValue());
if(!bean.getClass().isAnnotationPresent(CWController.class)) {
continue;
}
// 基本路径
String basePath = "";
if(bean.getClass().isAnnotationPresent(CWRequestMapping.class)) {
basePath = ((CWRequestMapping)bean.getClass().getAnnotation(CWRequestMapping.class)).value();
}
System.out.println("=========>basePath:"+basePath);
// 方法路径
Method[] methods = bean.getClass().getMethods();
for(Method method:methods) {
if(method.isAnnotationPresent(CWRequestMapping.class)) {
String path = ((CWRequestMapping)method.getAnnotation(CWRequestMapping.class)).value();
requestMap.put(("/"+basePath +"/"+path).replaceAll("/+", "/"), method);
}
}
}
}
5、处理页面请求
private void doDispatch(HttpServletRequest req, HttpServletResponse resp) throws UnsupportedEncodingException, IOException {
String url = req.getRequestURI();
String contextPath = req.getContextPath();
url = url.replace(contextPath, "").replaceAll("/+", "/");
System.out.println("=========>request url:"+url);
Method method = this.requestMap.get(url);
if(null == method) {
resp.getOutputStream().write("404 not found!".getBytes("UTF-8"));
return;
}
String beanName = this.lowerFirstChar(method.getDeclaringClass().getSimpleName());
try {
method.invoke(beanFactory.get(beanName), req,resp);
}catch (Exception e) {
e.printStackTrace();
resp.getOutputStream().write("404 not found!".getBytes("UTF-8"));
}
}
6、添加测试类了
HelloWorldAction.java
@CWController
@CWRequestMapping("/h")
public class HelloWorldAction {
@CWAutowired
private IUserService userService;
@CWRequestMapping("/hello.htm")
public void hello(HttpServletRequest request,HttpServletResponse response) {
try {
System.out.println(userService.getUserNameById(1L));
response.getWriter().write("hello World!");
response.flushBuffer();
} catch (IOException e) {
e.printStackTrace();
}
}
}
IUserService.java
public interface IUserService {
public String getUserNameById(Long id);
}
UserServiceImpl.java
@CWService
public class UserServiceImpl implements IUserService {
@Override
public String getUserNameById(Long id) {
return "master";
}
}
7、tomcat启动，大功告成
http:127.0.0.1:8080/h/hello.htm
总结：
1、看别人的代码，很简单，自己实现就发现很多坑。关键还是要自己实践。实践！实践！实践！
备注:
1、参考来源
https://www.toutiao.com/i6636629045259796995/
2、工程源码
https://pan.baidu.com/s/1F0el_nwDJ99-AYueeH0esw
原文：https://www.cnblogs.com/chewq/p/10165497.html