JSP&Servlet學習筆記----第1/2章

時間  2021-04-06
標籤 html java web apache api 瀏覽器 tomcat 服務器 cookie 架構 欄目 JSP 简体版
原文   原文鏈接

HTML(HyperText Markup Language)：超文本標記語言html

HTTP(HyperText Transfer Protocol)：超文本傳輸協議java

URL(Uniform Resource Locator)：統一資源定位符，以文字的方式來講明因特網上的資源如何取得。web

URN(Uniform Resource Name)：表明某個資源獨一無二的名稱，如圖書的ISBN。apache

URI(Uniform Resource Identifier)：URL和URN是URI的子集。api

一個簡單的html範例程序：瀏覽器

<!DOCTYPE html>
<html>
<head>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
    <title>HTML範例</title>
</head>
<body>
    <form method="get" action="hello.do" name="sample">
        姓名：
        <input type="text" name="name">
        <br />
        <button>發送</button>
    </form>
</body>
</html>
HTML學習資源： http://www.w3school.com.cn/html/index.asp

HTTP：指架構在TCP/IP之上應用層的一種協議。它的兩個特色：tomcat

一、無狀態（stateless）通訊協議。（無記憶性）服務器

二、基於請求（request）/響應（response）模型。cookie

客戶端對服務器發出一個取得資源的請求，服務器將要求的資源響應給客戶端，每次的聯機只做一次請求/響應，是一種很簡單的通訊協議，沒有請求就沒有響應。架構

在HTTP 協議下，服務器是個健忘的傢伙，服務器響應客戶端以後，就不會記得客戶端的信息，更不會去維護與客戶端有關的狀態，所以HTTP又稱爲無狀態的通訊協議。

瀏覽器在使用http發送請求，最重要的就是GET和POST。

GET：就是向服務器取得指定的資源。

POST請求：就是請求時發佈(POST)信息給服務器。

對於二者如何進行選擇？

一、get方式請求參數長度是有限的，過長的或者如文件上傳應該使用post請求。

二、get請求參數會出如今地址欄。

三、get請求純粹是爲了取得資源，而不改變服務器上的資源的狀態。而post相反。

對於java，JVM(java virtual machine)是java程序惟一認得的操做系統，其可執行文件爲.class文件。

對於JSP/Servlet，Web容器是JSP/Servlet惟一認得的http服務器。

URL編解碼：

import java.io.UnsupportedEncodingException;
import java.net.URLDecoder;
import java.net.URLEncoder;

/**
 * Created by N3verL4nd on 2017/1/2.
 */


public class HelloWorld
{
    public static void main(String[] args) throws UnsupportedEncodingException {
        System.out.println(URLEncoder.encode("http://www.baidu.com", "UTF-8"));
        System.out.println(URLDecoder.decode("%3A", "UTF-8"));
    }
}
URL編碼針對的字符是UTF-8編碼的8個位數值。

對於ascii字符使用1個字節，非ascii如中文使用3個字節。

import java.io.UnsupportedEncodingException;
import java.net.URLDecoder;
import java.net.URLEncoder;

/**
 * Created by N3verL4nd on 2017/1/2.
 */
public class HelloWorld
{
    public static void main(String[] args) throws UnsupportedEncodingException {
        System.out.println(URLEncoder.encode("我", "UTF-8"));
        System.out.println(URLDecoder.decode("%E6%88%91", "UTF-8"));
    }
}
HTTP規範下的URL編碼，並不限使用UTF-8，例如在一個BIG5網頁中，若窗體使用get發送中文，則是使用BIG5編碼的參數。 

System.out.println(URLEncoder.encode("我", "BIG5"));

第一個Servlet程序(打印http header)：

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Enumeration;

/**
 * Created by N3verL4nd on 2017/1/4.
 */
@WebServlet(name = "testServlet",urlPatterns = {"/test.do"})
public class testServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html;charset=UTF-8");
        PrintWriter out = response.getWriter();
        out.println("<html>");
        out.println("<head>");
        out.println("<title>TEST</title>");
        out.println("</head>");
        out.println("<body>");

        out.println("<h1>Hello World</h1>");

        out.println("</body>");
        out.println("</html>");
        out.close();
    }
}

/test.do
/Servlet
/Servlet/test.do host:localhost:8080
connection:keep-alive
upgrade-insecure-requests:1
user-agent:Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/55.0.2883.87 Safari/537.36
accept:text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8
accept-encoding:gzip, deflate, sdch, br
accept-language:zh-CN,zh;q=0.8
cookie:JSESSIONID=CDD8329D5BB881383911AC4CFAB4A159; Idea-e643fc73=b918ddfe-f8fa-43a0-b608-e1670a29b80a

@WebServlet(name = "testServlet",urlPatterns = {"/test.do"})
這表示該Servlet名稱爲testServlet，當請求的URL是/test.do，如http://localhost:8080/Servlet/test.do就會由testServlet處理。 
HttpServletRequest

表明請求對象，封裝了HTTP請求信息。

HttpServletResponse
表明對客戶端的響應。

Servlet的編譯(需servlet-api.jar。位於D:\Tomcat\apache-tomcat-9.0.0.M15\lib)：



一個簡易的Servlet程序對應的文件目錄結構以下：

E:\MyDocument\Desktop\jspRun\web\WEB-INF>tree /f
文件夾 PATH 列表
卷序列號爲 025427CF 32D1:7CF3
E:.
│  web.xml
│
├─classes
│      testServlet.class
│
└─lib


E:\MyDocument\Desktop\jspRun\web\WEB-INF>
部署：

將web.war拷貝到webapps目錄下（D:\Tomcat\apache-tomcat-9.0.0.M15\webapps ）

運行bin目錄下的startup.bat


servlet、genericservlet、httpservlet之間的關係：


package javax.servlet;
import java.io.IOException;
public interface Servlet {
    public void init(ServletConfig config) throws ServletException;
    public ServletConfig getServletConfig();
    public void service(ServletRequest req, ServletResponse res)
            throws ServletException, IOException;
    public String getServletInfo();
    public void destroy();
}

package javax.servlet;
import java.io.IOException;
import java.util.Enumeration;
public abstract class GenericServlet implements Servlet, ServletConfig,
        java.io.Serializable {

    private static final long serialVersionUID = 1L;

    private transient ServletConfig config;
    public GenericServlet() {
        // NOOP
    }
    @Override
    public void destroy() {
        // NOOP by default
    }
    @Override
    public String getInitParameter(String name) {
        return getServletConfig().getInitParameter(name);
    }
    @Override
    public Enumeration<String> getInitParameterNames() {
        return getServletConfig().getInitParameterNames();
    }
    @Override
    public ServletConfig getServletConfig() {
        return config;
    }
    @Override
    public ServletContext getServletContext() {
        return getServletConfig().getServletContext();
    }
    @Override
    public String getServletInfo() {
        return "";
    }
    @Override
    public void init(ServletConfig config) throws ServletException {
        this.config = config;
        this.init();
    }
    public void init() throws ServletException {
        // NOOP by default
    }

    public void log(String msg) {
        getServletContext().log(getServletName() + ": " + msg);
    }
    public void log(String message, Throwable t) {
        getServletContext().log(getServletName() + ": " + message, t);
    }
    @Override
    public abstract void service(ServletRequest req, ServletResponse res)
            throws ServletException, IOException;
    @Override
    public String getServletName() {
        return config.getServletName();
    }
}
package javax.servlet.http;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.io.UnsupportedEncodingException;
import java.lang.reflect.Method;
import java.text.MessageFormat;
import java.util.Enumeration;
import java.util.ResourceBundle;
import javax.servlet.DispatcherType;
import javax.servlet.GenericServlet;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
public abstract class HttpServlet extends GenericServlet {
    private static final long serialVersionUID = 1L;
    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 final ResourceBundle lStrings =
        ResourceBundle.getBundle(LSTRING_FILE);
    public HttpServlet() {
        // NOOP
    }
    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(HttpServletResponse.SC_METHOD_NOT_ALLOWED, msg);
        } else {
            resp.sendError(HttpServletResponse.SC_BAD_REQUEST, msg);
        }
    }
    protected long getLastModified(HttpServletRequest req) {
        return -1;
    }
    protected void doHead(HttpServletRequest req, HttpServletResponse resp)
        throws ServletException, IOException {

        if (DispatcherType.INCLUDE.equals(req.getDispatcherType())) {
            doGet(req, resp);
        } else {
            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(HttpServletResponse.SC_METHOD_NOT_ALLOWED, msg);
        } else {
            resp.sendError(HttpServletResponse.SC_BAD_REQUEST, msg);
        }
    }
    ...
}
Servlet接口：定義了Servlet應當有的基本行爲，全部的Servlet程序都必須實現Servlet接口（GenericServlet或者HttpServlet）。

GenericServlet：實現了Servlet接口，沒有規範任何與HTTP相關的方法，而是由繼承它的HttpServlet來定義。

HttpServlet的service方法流程：

protected void service(HttpServletRequest req, HttpServletResponse resp)
    throws ServletException, IOException {

    String method = req.getMethod();

    if (method.equals(METHOD_GET)) {
        long lastModified = getLastModified(req);
        if (lastModified == -1) {
            // servlet doesn't support if-modified-since, no reason
            // to go through further expensive logic
            doGet(req, resp);
        } else {
            long ifModifiedSince;
            try {
                ifModifiedSince = req.getDateHeader(HEADER_IFMODSINCE);
            } catch (IllegalArgumentException iae) {
                // Invalid date header - proceed as if none was set
                ifModifiedSince = -1;
            }
            if (ifModifiedSince < (lastModified / 1000 * 1000)) {
                // If the servlet mod time is later, call doGet()
                // Round down to the nearest second for a proper compare
                // A ifModifiedSince of -1 will always be less
                maybeSetLastModified(resp, lastModified);
                doGet(req, resp);
            } else {
                resp.setStatus(HttpServletResponse.SC_NOT_MODIFIED);
            }
        }

    } else if (method.equals(METHOD_HEAD)) {
        long lastModified = getLastModified(req);
        maybeSetLastModified(resp, lastModified);
        doHead(req, resp);

    } else if (method.equals(METHOD_POST)) {
        doPost(req, resp);

    } else if (method.equals(METHOD_PUT)) {
        doPut(req, resp);

    } else if (method.equals(METHOD_DELETE)) {
        doDelete(req, resp);

    } else if (method.equals(METHOD_OPTIONS)) {
        doOptions(req,resp);

    } else if (method.equals(METHOD_TRACE)) {
        doTrace(req,resp);

    } else {
        //
        // Note that this means NO servlet supports whatever
        // method was requested, anywhere on this server.
        //

        String errMsg = lStrings.getString("http.method_not_implemented");
        Object[] errArgs = new Object[1];
        errArgs[0] = method;
        errMsg = MessageFormat.format(errMsg, errArgs);

        resp.sendError(HttpServletResponse.SC_NOT_IMPLEMENTED, errMsg);
}
}
當請求到來時，容器會調用Servlet的service()方法。
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