SpringMVC源码深度解析之HandlerAdapter适配器模式源码分析
什么是适配器模式
定义：将一个系统的接口转换成另外一种形式，从而使原来不能直接调用的接口变得可以调用。
适配器模式应用场景
- Mybatis多种日志框架的整合
- SpringMVC适配器模式
- 新老版本的兼容问题
SpringMVC适配器模式源码分析
1、通过URL找到具体的请求方法
mappedHandler = this.getHandler(processedRequest);2、使用getHandlerAdapter获取对应的hanlder的具体HandlerAdapter,然后通过具体的适配器执行方法
HandlerAdapter ha = this.getHandlerAdapter(mappedHandler.getHandler());在这里进行初始化三个适配器
先走父类
返回true
protected boolean supportsInternal(HandlerMethod handlerMethod) {
return true;
}拿到对应的适配器
HandlerAdapter接口看下所有适配器类型
下面看下这几种适配器：
AbstractHandlerMethodAdapter implements HandlerAdapter
public final boolean supports(Object handler) {
return handler instanceof HandlerMethod && this.supportsInternal((HandlerMethod)handler);
}HttpRequestHandlerAdapter implements HandlerAdapter
public boolean supports(Object handler) {
return handler instanceof HttpRequestHandler;
}RequestMappingHandlerAdapter extends AbstractHandlerMethodAdapter
protected boolean supportsInternal(HandlerMethod handlerMethod) {
return true;
}SimpleControllerHandlerAdapter implements HandlerAdapter
public boolean supports(Object handler) {
return handler instanceof Controller;
}SimpleServletHandlerAdapter implements HandlerAdapter
public boolean supports(Object handler) {
return handler instanceof Servlet;
}- 继承Controller方式所使用的适配器：SimpleControllerHandlerAdapter
- HTTP请求处理器适配器：HttpRequestHandlerAdapter
- 注解方式（@Controller）的处理器适配器：RequestMappingHandlerAdapter
如果不采用适配器的话
If(hanlder instanceof Controller){
// 执行Controller适配器
}
If(hanlder instanceof HttpControler){
// 执行我们的HttpController
}
If(hanlder instanceof ServletControler){
// 执行我们的HttpController
}
If(hanlder instanceof AnnotationControler){
// 执行我们的AnnotationController
}简单实现接口
@Controller("/httpRequestHandler")
public class ExtHttpRequestHandlerAdapter implements HttpRequestHandler {
@Override
public void handleRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
System.out.println("httpRequestHandler");
}
}这个时候就会执行到HttpRequestHandlerAdapter适配器
模拟SpringMVC适配器模式
HandlerAdapter
public interface HandlerAdapter {
/**
* 根据hanlder判断是那个HandlerAdapter类型 如果找到对应的类型话返回true
*/
boolean supports(Object handler);
/**
* 执行我们的请求方法
*/
void handle(Object handler);
}HandlerAdapter子类
public class AnnotationHandlerAdapter implements HandlerAdapter {
/**
* 注解形式的适配器
*/
public boolean supports(Object handler) {
return (handler instanceof AnnotationController);
}
public void handle(Object handler) {
((AnnotationController) handler).hanlder();
}
}public class HttpRequestHandlerAdapter implements HandlerAdapter {
/**
* Http类型 适配器
*/
public boolean supports(Object handler) {
return (handler instanceof HttpController);
}
public void handle(Object handler) {
((HttpController) handler).hanlder();
}
}Controller
public interface Controller {
//请求方法
void hanlder();
}Controller子类
public class AnnotationController implements Controller {
public void hanlder() {
System.out.println("AnnotationController");
}
}public class HttpController implements Controller {
public void hanlder() {
System.out.println("HttpController");
}
}DispatcherServlet
public class DispatcherServlet {
private List<HandlerAdapter> handlerAdapters;
public DispatcherServlet() {
handlerAdapters = new ArrayList<HandlerAdapter>();
handlerAdapters.add(new HttpRequestHandlerAdapter());
handlerAdapters.add(new AnnotationHandlerAdapter());
}
public void dispatcher() {
// 1. 已经获取到hanlder
AnnotationController hanlder = new AnnotationController();
// 2.获取具体适配器
HandlerAdapter handlerAdapter = getHandlerAdapter(hanlder);
// 3.执行我们的请求方案
handlerAdapter.handle(hanlder);
}
public HandlerAdapter getHandlerAdapter(Controller controller) {
if (this.handlerAdapters != null) {
for (HandlerAdapter ha : this.handlerAdapters) {
if (ha.supports(controller)) {
return ha;
}
}
}
return null;
}
public static void main(String[] args) {
new DispatcherServlet().dispatcher();
}
}本文参考：
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