這篇文章主要講解了“如何對HttpServletRequest中的Header進行增刪”，文中的講解內(nèi)容簡單清晰，易于學習與理解，下面請大家跟著小編的思路慢慢深入，一起來研究和學習“如何對HttpServletRequest中的Header進行增刪”吧！
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HttpServletRequest中定義的對Header的操作全是只讀，沒有修改。
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public interface HttpServletRequest extends ServletRequest {
...
public long getDateHeader(String name);
public String getHeader(String name);
public Enumeration getHeaders(String name);
public Enumeration getHeaderNames();
public int getIntHeader(String name);
...
} HttpServletRequest 只是一個接口，實現(xiàn)由Servlet容器提供。不管是任何容器，實現(xiàn)類，肯定是要把請求的Header存儲在某個地方，于是可以通過反射來對存儲Header的容器進行增刪。
這個Controller很簡單，把客戶端的所有Header，以JSON形似響應(yīng)給客戶端。
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 {
// 遍歷所有請求Header，響應(yīng)給客戶端。 map
@GetMapping
public Object demo (HttpServletRequest request) {
Map> headers = new LinkedHashMap<>();
Enumeration nameEnumeration = request.getHeaderNames();
while (nameEnumeration.hasMoreElements()) {
String name = nameEnumeration.nextElement();
List values = headers.get(name);
if (values == null) {
values = new ArrayList<>();
headers.put(name, values);
}
Enumeration valueEnumeration = request.getHeaders(name);
while (valueEnumeration.hasMoreElements()) {
values.add(valueEnumeration.nextElement());
}
}
return headers;
}
} Tomcat使用了外觀模式（Facade），這個實現(xiàn)稍微有一點點復(fù)雜
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 實現(xiàn)，它有一個org.apache.catalina.connector.Request 的對象。這個對象又有一個org.apache.coyote.Request的對象，這個對象又有一個org.apache.tomcat.util.http.MimeHeaders 字段，它就是存儲了客戶端請求頭的容器，只要通過反射獲取到這個MimeHeaders，對它進行修改即可。
public class RequestFacade implements HttpServletRequest {
protected org.apache.catalina.connector.Request request = null;
...
}public class Request implements HttpServletRequest {
protected org.apache.coyote.Request coyoteRequest;
...
}public final class Request {
private final org.apache.tomcat.util.http.MimeHeaders headers = new MimeHeaders();
}假設(shè)的場景是，需要對請求Header統(tǒng)一添加一個
x-request-id，通過這個ID來從日志中定位每一個請求。
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 {
// 從 RequestFacade 中獲取 org.apache.catalina.connector.Request
Field connectorField = ReflectionUtils.findField(RequestFacade.class, "request", Request.class);
connectorField.setAccessible(true);
Request connectorRequest = (Request) connectorField.get(req);
// 從 org.apache.catalina.connector.Request 中獲取 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);
// 從 org.apache.coyote.Request 中獲取 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) {
// 添加一個Header，隨機生成請求ID
mimeHeaders.addValue("x-request-id").setString(UUID.randomUUID().toString());;
// 移除一個header
mimeHeaders.removeHeader("User-Agent");
}
}
可以看到成功添加了x-request-id header，并且刪除了User-Agent header。
SpringBoot默認的Servlet容器就是Tomcat
越來越多人使用Undertow作為Servlet容器，據(jù)說性能比Tomcat要好很多
只需要把spring-boot-starter-web中的spring-boot-starter-tomcat排除，然后手動添加spring-boot-starter-undertow即可
org.springframework.boot spring-boot-starter-web org.springframework.boot spring-boot-starter-tomcat org.springframework.boot spring-boot-starter-undertow
HttpServletRequest實現(xiàn)它的實現(xiàn)就比較簡單
io.undertow.servlet.spec.HttpServletRequestImpl |-io.undertow.server.HttpServerExchange |-io.undertow.util.HeaderMap
io.undertow.servlet.spec.HttpServletRequestImpl實現(xiàn)類中有一個屬性對象io.undertow.server.HttpServerExchange，這個屬性對象又包含了一個io.undertow.util.HeaderMap，HeaderMap就是請求Header的存儲容器，反射獲取它就行。
public final class HttpServletRequestImpl implements HttpServletRequest {
private final io.undertow.server.HttpServerExchange exchange;
}public final class HttpServerExchange extends AbstractAttachable {
private final HeaderMap requestHeaders;
}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 {
// 從HttpServletRequestImpl中獲取HttpServerExchange
Field exchangeField = ReflectionUtils.findField(HttpServletRequestImpl.class, "exchange", HttpServerExchange.class);
exchangeField.setAccessible(true);
HttpServerExchange httpServerExchange = (HttpServerExchange) exchangeField.get(req);
// 從HttpServerExchange中獲取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");
}
}
感謝各位的閱讀，以上就是“如何對HttpServletRequest中的Header進行增刪”的內(nèi)容了，經(jīng)過本文的學習后，相信大家對如何對HttpServletRequest中的Header進行增刪這一問題有了更深刻的體會，具體使用情況還需要大家實踐驗證。這里是創(chuàng)新互聯(lián)，小編將為大家推送更多相關(guān)知識點的文章，歡迎關(guān)注！
