JSP&Servlet学习笔记----第1/2章

时间  2021-04-06
标签 html java web apache api 浏览器 tomcat 服务器 cookie 架构 栏目 JSP 繁體版
原文   原文链接

HTML(HyperText Markup Language)：超文本标记语言html

HTTP(HyperText Transfer Protocol)：超文本传输协议java

URL(Uniform Resource Locator)：统一资源定位符，以文字的方式来讲明因特网上的资源如何取得。web

URN(Uniform Resource Name)：表明某个资源独一无二的名称，如图书的ISBN。apache

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

一个简单的html范例程序：浏览器

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

HTTP：指架构在TCP/IP之上应用层的一种协议。它的两个特色：tomcat

一、无状态（stateless）通讯协议。（无记忆性）服务器

二、基于请求（request）/响应（response）模型。cookie

客户端对服务器发出一个取得资源的请求，服务器将要求的资源响应给客户端，每次的联机只做一次请求/响应，是一种很简单的通讯协议，没有请求就没有响应。架构

在HTTP 协议下，服务器是个健忘的家伙，服务器响应客户端以后，就不会记得客户端的信息，更不会去维护与客户端有关的状态，所以HTTP又称为无状态的通讯协议。

浏览器在使用http发送请求，最重要的就是GET和POST。

GET：就是向服务器取得指定的资源。

POST请求：就是请求时发布(POST)信息给服务器。

对于二者如何进行选择？

一、get方式请求参数长度是有限的，过长的或者如文件上传应该使用post请求。

二、get请求参数会出如今地址栏。

三、get请求纯粹是为了取得资源，而不改变服务器上的资源的状态。而post相反。

对于java，JVM(java virtual machine)是java程序惟一认得的操做系统，其可执行文件为.class文件。

对于JSP/Servlet，Web容器是JSP/Servlet惟一认得的http服务器。

URL编解码：

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编码针对的字符是UTF-8编码的8个位数值。

对于ascii字符使用1个字节，非ascii如中文使用3个字节。

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规范下的URL编码，并不限使用UTF-8，例如在一个BIG5网页中，若窗体使用get发送中文，则是使用BIG5编码的参数。 

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

第一个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"})
这表示该Servlet名称为testServlet，当请求的URL是/test.do，如http://localhost:8080/Servlet/test.do就会由testServlet处理。 
HttpServletRequest

表明请求对象，封装了HTTP请求信息。

HttpServletResponse
表明对客户端的响应。

Servlet的编译(需servlet-api.jar。位于D:\Tomcat\apache-tomcat-9.0.0.M15\lib)：



一个简易的Servlet程序对应的文件目录结构以下：

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


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

将web.war拷贝到webapps目录下（D:\Tomcat\apache-tomcat-9.0.0.M15\webapps ）

运行bin目录下的startup.bat


servlet、genericservlet、httpservlet之间的关系：


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：定义了Servlet应当有的基本行为，全部的Servlet程序都必须实现Servlet接口（GenericServlet或者HttpServlet）。

GenericServlet：实现了Servlet接口，没有规范任何与HTTP相关的方法，而是由继承它的HttpServlet来定义。

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);
}
}
当请求到来时，容器会调用Servlet的service()方法。
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