对HttpServletRequest中的Header进行增删

HttpServletRequest 没有提供修改/删除的 Api

HttpServletRequest中定义的对 Header 的操作全是只读，没有修改。代码实现如下：

public interface HttpServletRequest extends ServletRequest {
   
    ...
    public long getDateHeader(String name);
    public String getHeader(String name);
    public Enumeration<String> getHeaders(String name);
    public Enumeration<String> getHeaderNames();
    public int getIntHeader(String name);
    ...
}

HttpServletRequest 只是一个接口，实现由 Servlet 容器提供。不管是任何容器，实现类，肯定是要把请求的 Header 存储在某个地方，于是可以通过反射来对存储Header的容器进行增删。

先定义一个测试的 Controller

这个 Controller 很简单，把客户端的所有 Header，以 JSON 形似响应给客户端。

import java.util.ArrayList;
import java.util.Enumeration;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;

import javax.servlet.http.HttpServletRequest;

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
@RequestMapping("/demo")
public class DemoController {
   

    // 遍历所有请求Header，响应给客户端。 map<string, string[]>
    @GetMapping
    public Object demo (HttpServletRequest request) {
   
        Map<String, List<String>> headers = new LinkedHashMap<>();
        Enumeration<String> nameEnumeration = request.getHeaderNames();
        while (nameEnumeration.hasMoreElements()) {
   
            String name = nameEnumeration.nextElement();
            List<String> values = headers.get(name);
            if (values == null) {
   
                values = new ArrayList<>();
                headers.put(name, values);
            }
            Enumeration<String> valueEnumeration = request.getHeaders(name);
            while (valueEnumeration.hasMoreElements()) {
   
                values.add(valueEnumeration.nextElement());
            }
        }
        return headers;
    }
}

使用 Tomcat 作为容器

Tomcat 对 HttpServletRequest 的实现

Tomcat 使用了外观模式（Facade），这个实现稍微有一点点复杂

org.apache.catalina.connector.RequestFacade
|-org.apache.catalina.connector.Request
  |-org.apache.coyote.Request
    |-org.apache.tomcat.util.http.MimeHeaders

首先是 org.apache.catalina.connector.RequestFacade 实现，它有一个org.apache.catalina.connector.Request 的对象。这个对象又有一个org.apache.coyote.Request的对象，这个对象又有一个org.apache.tomcat.util.http.MimeHeaders 字段，它就是存储了客户端请求头的容器，只要通过反射获取到这个MimeHeaders，对它进行修改即可。

org.apache.catalina.connector.RequestFacade

public class RequestFacade implements HttpServletRequest {
   
    protected org.apache.catalina.connector.Request request = null;
    ...
}

org.apache.catalina.connector.Request

public class Request implements HttpServletRequest {
   
    protected org.apache.coyote.Request coyoteRequest;
    ...
}

org.apache.coyote.Request coyoteRequest

public final class Request {
   
    private final org.apache.tomcat.util.http.MimeHeaders headers = new MimeHeaders();
}

在 Filter 中通过反射对请求 Header 进行增删

假设的场景是，需要对请求 Header 统一添加一个x-request-id，通过这个 ID 来从日志中定位每一个请求。

import java.io.IOException;
import java.lang.reflect.Field;
import java.util.UUID;

import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.catalina.connector.Request;
import org.apache.catalina.connector.RequestFacade;
import org.apache.tomcat.util.http.MimeHeaders;
import org.springframework.core.annotation.Order;
import org.springframework.stereotype.Component;
import org.springframework.util.ReflectionUtils;



@WebFilter(urlPatterns = "/*")
@Component
@Order(-999)
public class RequestIdGenFilter extends HttpFilter {
   

    /**
     *
     */
    private static final long serialVersionUID = 1787347739651657706L;

    @Override
    protected void doFilter(HttpServletRequest req, HttpServletResponse res, FilterChain chain) throws IOException, ServletException {
   
        try {
   
            // 从 RequestFacade 中获取 org.apache.catalina.connector.Request
            Field connectorField = ReflectionUtils.findField(RequestFacade.class, "request", Request.class);
            connectorField.setAccessible(true);
            Request connectorRequest = (Request) connectorField.get(req);

            // 从 org.apache.catalina.connector.Request 中获取 org.apache.coyote.Request
            Field coyoteField = ReflectionUtils.findField(Request.class, "coyoteRequest", org.apache.coyote.Request.class);
            coyoteField.setAccessible(true);
            org.apache.coyote.Request coyoteRequest = (org.apache.coyote.Request) coyoteField.get(connectorRequest);

            // 从 org.apache.coyote.Request 中获取 MimeHeaders
            Field mimeHeadersField =  ReflectionUtils.findField(org.apache.coyote.Request.class, "headers", MimeHeaders.class);
            mimeHeadersField.setAccessible(true);
            MimeHeaders mimeHeaders =  (MimeHeaders) mimeHeadersField.get(coyoteRequest);

            this.mineHeadersHandle(mimeHeaders);
        } catch (Exception e) {
   
            throw new RuntimeException(e);
        }
        super.doFilter(req, res, chain);
    }

    protected void mineHeadersHandle (MimeHeaders mimeHeaders) {
   
        // 添加一个Header，随机生成请求ID
        mimeHeaders.addValue("x-request-id").setString(UUID.randomUUID().toString());;
        // 移除一个header
        mimeHeaders.removeHeader("User-Agent");
    }
}

请求 Controller 获取响应结果

可以看到成功添加了x-request-id header，并且删除了User-Agent header。

使用 Undertow 作为容器

越来越多人使用 Undertow 作为 Servlet 容器，据说性能比 Tomcat 要好很多

SpringBoot 替换 Tomcat 为 Undertow

只需要把spring-boot-starter-web中的spring-boot-starter-tomcat排除，然后手动添加spring-boot-starter-undertow即可

<dependencies>
  <dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
    <exclusions>
      <exclusion>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-tomcat</artifactId>
      </exclusion>
    </exclusions>
  </dependency>
  <dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-undertow</artifactId>
  </dependency>
</dependencies>

Undertow 中的HttpServletRequest实现

它的实现就比较简单，结构如下：

io.undertow.servlet.spec.HttpServletRequestImpl
|-io.undertow.server.HttpServerExchange
  |-io.undertow.util.HeaderMap

io.undertow.servlet.spec.HttpServletRequestImpl实现类中有一个属性对象

io.undertow.server.HttpServerExchange，这个属性对象又包含了一个io.undertow.util.HeaderMap，HeaderMap就是请求 Header 的存储容器，反射获取它就行。

io.undertow.servlet.spec.HttpServletRequestImpl

public final class HttpServletRequestImpl implements HttpServletRequest {
   
    private final io.undertow.server.HttpServerExchange exchange;
}

io.undertow.server.HttpServerExchange

public final class HttpServerExchange extends AbstractAttachable {
   
    private final HeaderMap requestHeaders;
}

在 Filter 中通过反射对请求 Header 进行增删

import java.io.IOException;
import java.lang.reflect.Field;
import java.util.UUID;

import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.core.annotation.Order;
import org.springframework.stereotype.Component;
import org.springframework.util.ReflectionUtils;

import io.undertow.server.HttpServerExchange;
import io.undertow.servlet.spec.HttpServletRequestImpl;
import io.undertow.util.HeaderMap;
import io.undertow.util.HttpString;



@WebFilter(urlPatterns = "/*")
@Component
@Order(-999)
public class RequestIdGenFilter extends HttpFilter {
   

    /**
     *
     */
    private static final long serialVersionUID = 1787347739651657706L;

    @Override
    protected void doFilter(HttpServletRequest req, HttpServletResponse res, FilterChain chain) throws IOException, ServletException {
   
        try {
   
            // 从HttpServletRequestImpl中获取HttpServerExchange
            Field exchangeField = ReflectionUtils.findField(HttpServletRequestImpl.class, "exchange", HttpServerExchange.class);
            exchangeField.setAccessible(true);
            HttpServerExchange httpServerExchange = (HttpServerExchange) exchangeField.get(req);

            // 从HttpServerExchange中获取HeaderMap
            Field headerMapField = ReflectionUtils.findField(HttpServerExchange.class, "requestHeaders", HeaderMap.class);
            headerMapField.setAccessible(true);

            HeaderMap requestHeaderMap = (HeaderMap) headerMapField.get(httpServerExchange);
            this.handleRequestHeaderMap(requestHeaderMap);
        } catch (Exception e) {
   
            throw new RuntimeException(e);
        }
        super.doFilter(req, res, chain);
    }

    private void handleRequestHeaderMap(HeaderMap requestHeaderMap) {
   
        // 添加Header
        requestHeaderMap.add(new HttpString("x-request-id"), UUID.randomUUID().toString());
        // 移除Header
        requestHeaderMap.remove("User-Agent");
    }
}

请求 Controller 获取结果

结语

还有其他的 Servlet 容器，例如 Jetty。只要熟悉基本的反射，实现对请求头的增删，都很简单。

原文链接：https://forum.springdoc.cn/t/topic/3643

如有问题，欢迎微信搜索【码上遇见你】。

好了，本章节到此告一段落。希望对你有所帮助，祝学习顺利。