標籤：stat out 生命週期 tps this pre and hello 對象
1、把Java放到HTML中，JSP應運而生。
2、Servlet本身並沒有main()方法，所以必須要有其他Java程式去調用它，這個Java程式就是Web容器（Container）。Tomcat就是一個容器。
3、容器能提供什嗎？
4、容器如何處理請求？
Ⅰ、使用者發出一個指向Servlet的請求。
Ⅱ、容器“看出”這個請求指向Servlet，於是建立兩個對象HttpServletRequest、HttpServletResponse。
Ⅲ、容器找到這個Servlet，為其建立或者分配一個線程，並傳入上述兩個對象。
Ⅳ、容器調用Servlet的service()方法。
protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { String method = req.getMethod(); long lastModified; if(method.equals("GET")) { lastModified = this.getLastModified(req); if(lastModified == -1L) { this.doGet(req, resp); } else { long ifModifiedSince; try { ifModifiedSince = req.getDateHeader("If-Modified-Since"); } catch (IllegalArgumentException var9) { ifModifiedSince = -1L; } if(ifModifiedSince < lastModified / 1000L * 1000L) { this.maybeSetLastModified(resp, lastModified); this.doGet(req, resp); } else { resp.setStatus(304); } } } else if(method.equals("HEAD")) { lastModified = this.getLastModified(req); this.maybeSetLastModified(resp, lastModified); this.doHead(req, resp); } else if(method.equals("POST")) { this.doPost(req, resp); } else if(method.equals("PUT")) { this.doPut(req, resp); } else if(method.equals("DELETE")) { this.doDelete(req, resp); } else if(method.equals("OPTIONS")) { this.doOptions(req, resp); } else if(method.equals("TRACE")) { this.doTrace(req, resp); } else { String errMsg = lStrings.getString("http.method_not_implemented"); Object[] errArgs = new Object[]{method}; errMsg = MessageFormat.format(errMsg, errArgs); resp.sendError(501, errMsg); } }
Ⅵ、根據請求的不同，service()會調用不同的方法，假設請求對應doGet()方法：
import javax.servlet.http.*;import java.io.*;import java.util.Date;public class Ch1Servlet extends HttpServlet { @Override public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException { PrintWriter out = response.getWriter(); Date today = new Date(); out.println("<html>" + "<body>" + "<h1 align=center>Hello Servlet</h1>" + "</br>" + today + "</body>" + "</html>" ); }}
Ⅶ、doGet()方法產生動態網頁面，並把它寫入response裡。
Ⅷ、線程結束，容器把response對象轉換為一個HTTP響應，然後清理不再用的對象。
【Head First Servlets and JSP】筆記1
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