SpringMVC源碼深度解析之HandlerAdapter適配器模式源碼分析

SpringMVC中的HandlerAdapter適配器

什麼是適配器模式

定義：將一個系統的接口轉換成另一種形式，從而使原來不能直接調用的接口變得能夠調用。

適配器模式應用場景

• Mybatis多種日誌框架的整合
• SpringMVC適配器模式
• 新老版本的兼容問題

SpringMVC適配器模式源碼分析

一、經過URL找到具體的請求方法

mappedHandler = this.getHandler(processedRequest);

二、使用getHandlerAdapter獲取對應的hanlder的具體HandlerAdapter,而後經過具體的適配器執行方法

HandlerAdapter ha = this.getHandlerAdapter(mappedHandler.getHandler());

在這裏進行初始化三個適配器

先走父類

返回true

protected boolean supportsInternal(HandlerMethod handlerMethod) {
    return true;
}

拿到對應的適配器

HandlerAdapter接口看下全部適配器類型

下面看下這幾種適配器：

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;
}

• 繼承Controller方式所使用的適配器：SimpleControllerHandlerAdapter
• HTTP請求處理器適配器：HttpRequestHandlerAdapter
• 註解方式（@Controller）的處理器適配器：RequestMappingHandlerAdapter

若是不採用適配器的話

If(hanlder instanceof Controller){

 // 執行Controller適配器
}

If(hanlder instanceof  HttpControler){

 // 執行咱們的HttpController

}

If(hanlder instanceof  ServletControler){

 // 執行咱們的HttpController

}

If(hanlder instanceof  AnnotationControler){

 // 執行咱們的AnnotationController
}

簡單實現接口

@Controller("/httpRequestHandler")
public class ExtHttpRequestHandlerAdapter implements HttpRequestHandler {

    @Override
    public void handleRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("httpRequestHandler");
    }
}

這個時候就會執行到HttpRequestHandlerAdapter適配器

模擬SpringMVC適配器模式

HandlerAdapter

public interface HandlerAdapter {
    /**
     * 根據hanlder判斷是那個HandlerAdapter類型 若是找到對應的類型話返回true
     */
    boolean supports(Object handler);
    /**
     * 執行咱們的請求方法
     */
    void handle(Object handler);
}

HandlerAdapter子類

public class AnnotationHandlerAdapter implements HandlerAdapter {
    /**
     * 註解形式的適配器
     */
    public boolean supports(Object handler) {
        return (handler instanceof AnnotationController);
    }

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

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

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

Controller

public interface Controller {

    //請求方法
    void hanlder();
}

Controller子類

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. 已經獲取到hanlder
        AnnotationController hanlder = new AnnotationController();
     // 2.獲取具體適配器
        HandlerAdapter handlerAdapter = getHandlerAdapter(hanlder);
        // 3.執行咱們的請求方案
        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();
    }
}

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