開篇

• 這篇文章主要分析在 Tomcat的處理 http 請求的流程中干預 Request對象， 通過基于HttpServletRequestWrapper和 Filter組合進行干預。

• Tomcat 處理 http 請求的過程中 Request 對象是RequestFacade對象（可以通過 springBoot 中跟蹤tomcat-embed-core 的包進行跟蹤），干預后會設配成HttpServletRequestWrapper的子類對象進行傳遞。

• HttpServletRequestWrapper和RequestFacade都實現(xiàn) HttpServletRequest 接口。

Tomcat 處理流程

Tomcat 處理流程

• Tomcat 的針對 http請求的處理流程如上圖所示，在org.apache.catalina.core.ApplicationFilterChain#doFilter的方法中將org.apache.catalina.connector.Request封裝成了org.apache.catalina.connector.RequestFacade對象。
• 在后續(xù)的ApplicationFilterChain之后的執(zhí)行鏈路中使用的是RequestFacade對象。

Request 分析

Request

Request

package org.apache.catalina.connector;

public class Request implements org.apache.catalina.servlet4preview.http.HttpServletRequest {
}

------------------------------

package org.apache.catalina.servlet4preview.http;

public interface HttpServletRequest extends javax.servlet.http.HttpServletRequest {

    public ServletMapping getServletMapping();

    public PushBuilder newPushBuilder();
}

------------------------------

package javax.servlet.http;

public interface HttpServletRequest extends ServletRequest {
}

----------------------------------------

package javax.servlet;

public interface ServletRequest {
}

• Request 實現(xiàn)了javax.servlet.ServletRequest接口
• Request 實現(xiàn)了javax.servlet.http.HttpServletRequest接口

RequestFacade

RequestFacade

package org.apache.catalina.connector;

public class RequestFacade implements HttpServletRequest {

    public RequestFacade(Request request) {
        this.request = request;
    }

    protected Request request = null;
}

-------------------------------------

package org.apache.catalina.servlet4preview.http;

public interface HttpServletRequest extends javax.servlet.http.HttpServletRequest {

    public ServletMapping getServletMapping();
    public PushBuilder newPushBuilder();
}

-------------------------------------

package javax.servlet.http;

public interface HttpServletRequest extends ServletRequest {
}

----------------------------------------

package javax.servlet;

public interface ServletRequest {
}

• RequestFacade 實現(xiàn)了javax.servlet.ServletRequest接口
• RequestFacade 實現(xiàn)了javax.servlet.http.HttpServletRequest接口

HttpServletRequestWrapper

HttpServletRequestWrapper

package javax.servlet.http;

public class HttpServletRequestWrapper extends ServletRequestWrapper implements
        HttpServletRequest {

    public HttpServletRequestWrapper(HttpServletRequest request) {
        super(request);
    }
}

----------------------------------------

package javax.servlet;

public class ServletRequestWrapper implements ServletRequest {

    private ServletRequest request;

    public ServletRequestWrapper(ServletRequest request) {
        if (request == null) {
            throw new IllegalArgumentException("Request cannot be null");
        }
        this.request = request;
    }
}

----------------------------------------

package javax.servlet;

public interface ServletRequest {
}

• HttpServletRequestWrapper 實現(xiàn)了javax.servlet.ServletRequest接口

Request 改寫 Demo

import org.springframework.stereotype.Component;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;
import java.io.IOException;

@Component
public class WrapperFilter implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("wrapper filter init");
    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {

        WrapperDemo wrapperDemo = new WrapperDemo((HttpServletRequest)servletRequest);

        filterChain.doFilter(wrapperDemo, servletResponse);
    }

    @Override
    public void destroy() {
        System.out.println("wrapper filter init");
    }
}

---------------------------------

class WrapperDemo extends HttpServletRequestWrapper {

    public WrapperDemo(HttpServletRequest request) {
        super(request);
    }
}

• 自定義類WrapperDemo繼承HttpServletRequestWrapper，改寫getParameter相關的方法。
• 自定義WrapperFilter，在doFilter方法內(nèi)部將servletRequest（RequestFacade對象）強轉(zhuǎn)成HttpServletRequest后創(chuàng)建WrapperDemo對象后進行 Filter 的后續(xù)過濾，后續(xù) Filter 操作的 Request 對象是WrapperDemo對象。
• servletRequest（RequestFacade對象）能夠強轉(zhuǎn)成HttpServletRequest的原因是RequestFacade 實現(xiàn)了javax.servlet.http.HttpServletRequest接口。
• HttpServletRequestWrapper屬于HttpServletRequest的封裝類，內(nèi)部實現(xiàn)了所有HttpServletRequest的方法。

ServletWebRequest參數(shù)獲取

at org.apache.catalina.connector.Request.getParameter(Request.java:1140)
at org.apache.catalina.connector.RequestFacade.getParameter(RequestFacade.java:381)
at javax.servlet.ServletRequestWrapper.getParameter(ServletRequestWrapper.java:153)
at org.springframework.web.context.request.ServletWebRequest.getParameter(ServletWebRequest.java:154)

• ServletWebRequest獲取參數(shù)的流程本質(zhì)上執(zhí)行的是org.apache.catalina.connector.Request.getParameter的實現(xiàn)。
• 不管是 RequestFacade 或 ServletRequestWrapper等對請求的操作都是由org.apache.catalina.connector.Request.getParameter實現(xiàn)的。