关于servlet:对HttpServletRequest中的Header进行增删

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HttpServletRequest 没有提供批改 / 删除的 Api

HttpServletRequest中定义的对 Header 的操作全是只读，没有批改。

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。不论是任何容器，实现类，必定是要把申请的 Header 存储在某个中央，于是能够通过反射来对存储 Header 的容器进行增删。

先定义一个测试的 Controller

这个 Controller 很简略，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 {// 遍历所有申请 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;
    }
}

应用 Tomcat 作为容器

Tomcat 对 HttpServletRequest 的实现

Tomcat 应用了外观模式（Facade），这个实现略微有一点点简单

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申请头的容器，只有通过反射获取到这个MimeHeaders，对它进行批改即可。

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 中通过反射对申请 Header 进行增删

假如的场景是，须要对申请 Header 对立增加一个x-request-id，通过这个 ID 来从日志中定位每一个申请。

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) {
        // 增加一个 Header，随机生成申请 ID
        mimeHeaders.addValue("x-request-id").setString(UUID.randomUUID().toString());;
        // 移除一个 header
        mimeHeaders.removeHeader("User-Agent");
    }
}

申请 Controller 获取响应后果


能够看到胜利增加了x-request-id header，并且删除了User-Agent header。

SpringBoot 默认的 Servlet 容器就是 Tomcat

应用 Undertow 作为容器

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

SpringBoot 替换 Tomcat 为 Undertow

只须要把 spring-boot-starter-web 中的 spring-boot-starter-tomcat 排除，而后手动增加 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

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，这个属性对象又蕴含了一个io.undertow.util.HeaderMap，HeaderMap 就是申请 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 中通过反射对申请 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) {
        // 增加 Header
        requestHeaderMap.add(new HttpString("x-request-id"), UUID.randomUUID().toString());
        // 移除 Header
        requestHeaderMap.remove("User-Agent");
    }
}

申请 Controller 获取后果

最初

还有其余的 Servlet 容器，例如 Jetty。只有相熟根本的反射，实现对申请头的增删，都很简略。

原文：https://springboot.io/t/topic…

正文完
servlet
发表至： servlet
2021-05-10
 0
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