SpringMVC中的HandlerAdapter适配器

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

1If(hanlder instanceof Controller){
2
3 // 执行Controller适配器
4}
5
6If(hanlder instanceof  HttpControler){
7
8 // 执行我们的HttpController
9
10}
11
12If(hanlder instanceof  ServletControler){
13
14 // 执行我们的HttpController
15
16}
17
18If(hanlder instanceof  AnnotationControler){
19
20 // 执行我们的AnnotationController
21}
22

简单实现接口

1@Controller("/httpRequestHandler")
2public class ExtHttpRequestHandlerAdapter implements HttpRequestHandler {
3
4    @Override
5    public void handleRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
6        System.out.println("httpRequestHandler");
7    }
8}

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); }

1public void handle(Object handler) {
2    ((AnnotationController) handler).hanlder();
3}

}

public class HttpRequestHandlerAdapter implements HandlerAdapter { /** * Http类型适配器 */ public boolean supports(Object handler) { return (handler instanceof HttpController); }

1public void handle(Object handler) {
2    ((HttpController) handler).hanlder();
3}

}

Controller

public interface Controller {

1**//请求方法**
2void 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;

1public DispatcherServlet() {
2    handlerAdapters = new ArrayList<HandlerAdapter>();
3    handlerAdapters.add(new HttpRequestHandlerAdapter());
4    handlerAdapters.add(new AnnotationHandlerAdapter());
5}
6public void dispatcher() {
7    **// 1. 已经获取到hanlder**
8    AnnotationController hanlder = new AnnotationController();
9 **// 2.获取具体适配器**
10    HandlerAdapter handlerAdapter = getHandlerAdapter(hanlder);
11    **// 3.执行我们的请求方案**
12    handlerAdapter.handle(hanlder);
13}
14public HandlerAdapter getHandlerAdapter(Controller controller) {
15    if (this.handlerAdapters != null) {
16        for (HandlerAdapter ha : this.handlerAdapters) {
17
18            if (ha.supports(controller)) {
19                return ha;
20            }
21        }
22    }
23    return null;
24}
25public static void main(String\[\] args) {
26    new DispatcherServlet().dispatcher();
27}

}

本文参考：

蚂蚁课堂

http://www.mayikt.com/

SpringMVC源码深度解析之HandlerAdapter适配器模式源码分析