Servlet技术浅析（二）之HttpServlet抽象类

红太狼 2022-07-12 20:50 174阅读 0赞

HttpServlet抽象类是GenericServlet抽象类的子类，HttpServlet类为Servlet接口提供了与HTTP协议相关的通用实现，也就是说，HttpServlet对象适合运行在与客户端采用HTTP协议通信的Servlet容器或者Web服务器中。在开发javaWeb应用时，自定义的Servlet类一般都扩展HttpServlet类。

HttpServlet源码：

import java.io.IOException; import java.io.Serializable; import java.lang.reflect.Method; import java.text.MessageFormat; import java.util.Enumeration; import java.util.ResourceBundle; import javax.servlet.*; // Referenced classes of package javax.servlet.http: // NoBodyResponse, HttpServletRequest, HttpServletResponse public abstract class HttpServlet extends GenericServlet implements Serializable { public HttpServlet() { } protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { String protocol = req.getProtocol(); String msg = lStrings.getString("http.method_get_not_supported"); if(protocol.endsWith("1.1")) resp.sendError(405, msg); else resp.sendError(400, msg); } protected long getLastModified(HttpServletRequest req) { return -1L; } protected void doHead(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { NoBodyResponse response = new NoBodyResponse(resp); doGet(req, response); response.setContentLength(); } protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { String protocol = req.getProtocol(); String msg = lStrings.getString("http.method_post_not_supported"); if(protocol.endsWith("1.1")) resp.sendError(405, msg); else resp.sendError(400, msg); } protected void doPut(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { String protocol = req.getProtocol(); String msg = lStrings.getString("http.method_put_not_supported"); if(protocol.endsWith("1.1")) resp.sendError(405, msg); else resp.sendError(400, msg); } protected void doDelete(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { String protocol = req.getProtocol(); String msg = lStrings.getString("http.method_delete_not_supported"); if(protocol.endsWith("1.1")) resp.sendError(405, msg); else resp.sendError(400, msg); } private Method[] getAllDeclaredMethods(Class c) { if(c.equals(javax/servlet/http/HttpServlet)) return null; Method parentMethods[] = getAllDeclaredMethods(c.getSuperclass()); Method thisMethods[] = c.getDeclaredMethods(); if(parentMethods != null && parentMethods.length > 0) { Method allMethods[] = new Method[parentMethods.length + thisMethods.length]; System.arraycopy(parentMethods, 0, allMethods, 0, parentMethods.length); System.arraycopy(thisMethods, 0, allMethods, parentMethods.length, thisMethods.length); thisMethods = allMethods; } return thisMethods; } protected void doOptions(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { Method methods[] = getAllDeclaredMethods(getClass()); boolean ALLOW_GET = false; boolean ALLOW_HEAD = false; boolean ALLOW_POST = false; boolean ALLOW_PUT = false; boolean ALLOW_DELETE = false; boolean ALLOW_TRACE = true; boolean ALLOW_OPTIONS = true; for(int i = 0; i < methods.length; i++) { Method m = methods[i]; if(m.getName().equals("doGet")) { ALLOW_GET = true; ALLOW_HEAD = true; } if(m.getName().equals("doPost")) ALLOW_POST = true; if(m.getName().equals("doPut")) ALLOW_PUT = true; if(m.getName().equals("doDelete")) ALLOW_DELETE = true; } String allow = null; if(ALLOW_GET && allow == null) allow = "GET"; if(ALLOW_HEAD) if(allow == null) allow = "HEAD"; else allow = (new StringBuilder()).append(allow).append(", HEAD").toString(); if(ALLOW_POST) if(allow == null) allow = "POST"; else allow = (new StringBuilder()).append(allow).append(", POST").toString(); if(ALLOW_PUT) if(allow == null) allow = "PUT"; else allow = (new StringBuilder()).append(allow).append(", PUT").toString(); if(ALLOW_DELETE) if(allow == null) allow = "DELETE"; else allow = (new StringBuilder()).append(allow).append(", DELETE").toString(); if(ALLOW_TRACE) if(allow == null) allow = "TRACE"; else allow = (new StringBuilder()).append(allow).append(", TRACE").toString(); if(ALLOW_OPTIONS) if(allow == null) allow = "OPTIONS"; else allow = (new StringBuilder()).append(allow).append(", OPTIONS").toString(); resp.setHeader("Allow", allow); } protected void doTrace(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { String CRLF = "\r\n"; String responseString = (new StringBuilder()).append("TRACE ").append(req.getRequestURI()).append(" ").append(req.getProtocol()).toString(); for(Enumeration reqHeaderEnum = req.getHeaderNames(); reqHeaderEnum.hasMoreElements();) { String headerName = (String)reqHeaderEnum.nextElement(); responseString = (new StringBuilder()).append(responseString).append(CRLF).append(headerName).append(": ").append(req.getHeader(headerName)).toString(); } responseString = (new StringBuilder()).append(responseString).append(CRLF).toString(); int responseLength = responseString.length(); resp.setContentType("message/http"); resp.setContentLength(responseLength); ServletOutputStream out = resp.getOutputStream(); out.print(responseString); out.close(); } protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { String method = req.getMethod(); if(method.equals("GET")) { long lastModified = getLastModified(req); if(lastModified == -1L) { doGet(req, resp); } else { long ifModifiedSince = req.getDateHeader("If-Modified-Since"); if(ifModifiedSince < (lastModified / 1000L) * 1000L) { maybeSetLastModified(resp, lastModified); doGet(req, resp); } else { resp.setStatus(304); } } } else if(method.equals("HEAD")) { long lastModified = getLastModified(req); maybeSetLastModified(resp, lastModified); doHead(req, resp); } else if(method.equals("POST")) doPost(req, resp); else if(method.equals("PUT")) doPut(req, resp); else if(method.equals("DELETE")) doDelete(req, resp); else if(method.equals("OPTIONS")) doOptions(req, resp); else if(method.equals("TRACE")) { doTrace(req, resp); } else { String errMsg = lStrings.getString("http.method_not_implemented"); Object errArgs[] = new Object[1]; errArgs[0] = method; errMsg = MessageFormat.format(errMsg, errArgs); resp.sendError(501, errMsg); } } private void maybeSetLastModified(HttpServletResponse resp, long lastModified) { if(resp.containsHeader("Last-Modified")) return; if(lastModified >= 0L) resp.setDateHeader("Last-Modified", lastModified); } public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException { HttpServletRequest request; HttpServletResponse response; try { request = (HttpServletRequest)req; response = (HttpServletResponse)res; } catch(ClassCastException e) { throw new ServletException("non-HTTP request or response"); } service(request, response); } private static final String METHOD_DELETE = "DELETE"; private static final String METHOD_HEAD = "HEAD"; private static final String METHOD_GET = "GET"; private static final String METHOD_OPTIONS = "OPTIONS"; private static final String METHOD_POST = "POST"; private static final String METHOD_PUT = "PUT"; private static final String METHOD_TRACE = "TRACE"; private static final String HEADER_IFMODSINCE = "If-Modified-Since"; private static final String HEADER_LASTMOD = "Last-Modified"; private static final String LSTRING_FILE = "javax.servlet.http.LocalStrings"; private static ResourceBundle lStrings = ResourceBundle.getBundle("javax.servlet.http.LocalStrings"); }

通过HttpServlet的源码我们看到，HttpServlet与Servelt没有关联关系，而是继承了GenericServlet，其实GenericServlet是一个抽象类，该类已经实现了Servlet, ServletConfig, Serializable这三个接口，

Servlet源码和GenericServlet源码参见《[Servlet技术浅析一之GenericServlet抽象类][Servlet_GenericServlet]》

[Servlet_GenericServlet]: http://blog.csdn.net/u011159417/article/category/6655272