Java Web学习笔记 3 深入Servlet技术
第3章 深入Servlet技术
请求-响应模式就是典型的Web应用程序访问过程,Java Web应用程序中，处理请求并发送响应的过程是由一种叫做Servlet的程序来完成的。
请求request，响应response，与HTTP协议
Telnet演示HTTP协议
默认telnet关闭的，控制面板中，program and feathers，找到telnet client进行开启。
GET方式查询：常用来查询信息
HTTP头数据：
User-Ageent：Mozilla/4.0(...) 浏览器信息
Accept:text/html; */* 浏览器支持的格式
cookie: account-Helloween 记录用户当前的状态
Referer: http://www.baidu.com 指从哪个页面单击链接进入的
POST方式提交数据
GET提交数据不能超过256字符，POST提交，数据不在浏览器地址中显示，常用来提交表单数据
其他访问方式
HEAD,DELETE,TRACE,PUT,OPTIONS
Servlet概述
Java Web应用程序中所有的请求-响应都是Servlet完成的，没有main之类的方法，当用户访问服务器的时候，Tomcat通过调用Servlet的某些方法完成整个处理过程的。
Servlet工作流程
HttpServeltRequest/HttpServletResponse
Servlet接口
GET/POST/HEAD/PUT/DELETE/TRACE
一般为 doGet()/doPost() .../getLastModified(request)返回文档的最后修改时间
Java Web目录结构
Web程序部署在Tomcat的/webapps下面，用 http://localhost:8080/web1
编写Servlet
javax.servlet.* javax.servlet.http.*
一般直接继承HttpServlet，覆盖方法即可，一般只覆盖doGet(),doPost()
3.3.1 实现Servlet
编写Web Project，FirstServlet.java，覆盖常用三个方法
本书使用的是java EE5，新建项目时需要注意
新建web Project-> 新建servlet,
FirstServlet.java
/**
* The doGet method of the servlet.
*
* This method is called when a form has its tag value method equals to get.
*
* @param request the request send by the client to the server
* @param response the response send by the server to the client
* @throws ServletException if an error occurred
* @throws IOException if an error occurred
*
* GET方式访问页面执行该函数 执行doGet之前会执行getLastModified，如果发现返回的数值与上次访问是相同，
* 则认为文档没有更新，浏览器采用缓存而不执行，如果返回 -1，则认为最新，总是执行该函数
*/
public void doGet(HttpServletRequest request , HttpServletResponse response )
throws ServletException, IOException {
this.log("执行doGet方法..." );// 控制台日志输出信息
this.execute(request , response );// 处理doGet
}
/**
* The doPost method of the servlet.
*
* This method is called when a form has its tag value method equals to post.
*
* @param request the request send by the client to the server
* @param response the response send by the server to the client
* @throws ServletException if an error occurred
* @throws IOException if an error occurred
*
* 以post方式访问页面时执行该函数，执行前不会调用getLastModified
*/
public void doPost(HttpServletRequest request , HttpServletResponse response )
throws ServletException, IOException {
this.log("执行doPost方法" );
this.execute(request , response );
}
@Override
protected long getLastModified(HttpServletRequest req) {
// TODO Auto-generated method stub
this.log("执行 getLastModified 方法" );
return -1;
}
// 执行方法
private void execute(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException {
response.setCharacterEncoding( "UTF-8");
request.setCharacterEncoding( "UTF-8");
String requestURI = request.getRequestURI();
String method = request.getMethod();
String param = request.getParameter("param" );// 客户端提交的参数 param值
response.setContentType( "text/html");// 文档类型为HTML类型
PrintWriter out = response.getWriter();
out.println( "");
out.println( "");
out.println( " A Servlet ");
out.println( " ");
out.println( " 以" + method + " 方式访问该页面。取到的param参数为：" + param + "
" );
out.println( " " );
out.println( " " );
//客户端浏览器读取该文档的更新时间
out.println( " " );
out.println( " ");
out.println( "");
out.flush();
out.close();
}
3.3.2 配置
首先名称及类名：
FirstServlet
servlet.FirstServlet
message
welcome to FisrtServlet
encoding
utf-8
配置一个初始化参数
< load-on-startup>1
配置Servlet的加载方式。0和1,1启动加载，否则，Tomcat会在有人第一次请求加载
FirstServlet
/ servlet/FirstServlet
如果配置为/servlet/FirstServlet.* 使用http://localhost:8080/servlet /servlet/FirstServlet.XXX访问
通配符试了好像不行，还是支持多个映射，把需要的映射加进去吧
一个完整的servlet包括servlet类，配置，配置。利用myeclipse向导自动完成配置。
???部署到Tomcat6.0系统，然后启动，发现超时，可以使用：
部署的时候出现Server Tomcat v6.0 Server at localhost was unable to start within 45 seconds. If the server requires more time, try increasing the timeout in the server editor?
我们找到当前工程的workplace目录，然后按下面的操作：
找到workspace\.metadata\.plugins\org.eclipse.wst.server.core\servers.xml文件。
把其中的start-timeout="45" 改为 start-timeout="100" 或者更长，根据不同同学的工程大小来设置。
最后重启eclipse就可以了。
3.4 请求与响应
获取request变量
客户端浏览器发出的请求被封装HttpServletRequest对象，包含所有的信息。
在servlet项目中新建servlet,
RequestServlet.java：
public class RequestServlet extends HttpServlet {
/**
* Constructor of the object.
*/
public RequestServlet() {
super();
}
/**
* Destruction of the servlet.
*/
public void destroy() {
super.destroy(); // Just puts "destroy" string in log
// Put your code here
}
// 返回客户端浏览器接受的文件类型
private String getAccept(String accept) {
StringBuffer buffer = new StringBuffer();
if (accept .contains("image/gif"))
buffer.append( "GIF文件，");
if (accept .contains("image/x-xbitmap"))
buffer.append( "BMP文件，");
if (accept .contains("image/jpeg"))
buffer.append( "JPG文件，");
if (accept.contains("application/vnd.ms-execel" ))
buffer.append( "EXCEL文件，" );
if (accept.contains("application/vnd.ms-powerpoint" ))
buffer.append( "PPT文件，");
if (accept .contains("application/vnd.msword"))
buffer.append( "Word文件，" );
return buffer .toString().replaceAll(", $", "");
}
// 返回客户端的语言环境
private String getLocale(Locale locale) {
if (Locale.SIMPLIFIED_CHINESE.equals(locale))
return "简体中文" ;
if (Locale.TRADITIONAL_CHINESE.equals(locale))
return "繁体中文" ;
if (Locale.ENGLISH.equals(locale))
return "英文" ;
if (Locale.JAPANESE.equals(locale))
return "日文" ;
return "未知语言环境" ;
}
// 返回IP地址对应的物理地址
// private String getAddress(String ip){
// return IpUtil.getIpAddress(ip);
// }
// 返回客户端浏览器信息
private String getNavigatior(String userAgent) {
if (userAgent .indexOf("TencentTraveler") > 0)
return "腾讯浏览器" ;
if (userAgent .indexOf("Maxthon") > 0)
return "Maxthon浏览器" ;
if (userAgent .indexOf("MyIE2") > 0)
return "MyIE2浏览器" ;
if (userAgent .indexOf("Firefox") > 0)
return "Firefox浏览器" ;
if (userAgent .indexOf("MSIE") > 0)
return "IE浏览器" ;
return "未知浏览器" ;
}
// 返回客户端操作系统
private String getOS(String userAgent) {
if (userAgent .indexOf("Windows NT 5.1") > 0)
return "Windows XP" ;
if (userAgent .indexOf("Windows 98") > 0)
return "Windows 98" ;
if (userAgent .indexOf("Windows NT 5.0") > 0)
return "Windows 2000" ;
if (userAgent .indexOf("Linux") > 0)
return "Linux" ;
if (userAgent .indexOf("Unix") > 0)
return "Unix" ;
return "未知" ;
}
/**
* The doGet method of the servlet.
*
* This method is called when a form has its tag value method equals to get.
*
* @param request
* the request send by the client to the server
* @param response
* the response send by the server to the client
* @throws ServletException
* if an error occurred
* @throws IOException
* if an error occurred
*/
public void doGet(HttpServletRequest request , HttpServletResponse response )
throws ServletException, IOException {
request.setCharacterEncoding( "UTF-8");
response.setCharacterEncoding( "UTF-8");
response.setContentType( "text/html");//文档类型为HTML
String authType = request .getAuthType();
String localAddr = request .getLocalAddr();//本地IP，服务器IP
String localName = request .getLocalName();//本地名称，服务器名称
int localPort = request .getLocalPort();//本地端口，Tomcat端口
Locale locale = request.getLocale(); //用户的语言环境
String contextPath = request .getContextPath();
String method = request .getMethod();//get还是post
String pathInfo = request .getPathInfo();
String pathTranslated = request.getPathTranslated();
String protocol = request.getProtocol(); //协议，这里指HTTP协议
String queryString = request.getQueryString();//查询字符串，即？后面的字符串
String remoteAddr = request .getRemoteAddr();//远程IP，客户端IP
int port = request .getRemotePort();//远程端口，客户端端口
String remoteUser = request .getRemoteUser();//远程用户
String requestedSessionId = request.getRequestedSessionId();//客户端session的ID
String requestURI = request .getRequestURI();//用户请求的URI
StringBuffer requestURL = request.getRequestURL();//用户请求的URL
String scheme = request.getScheme(); //协议头，这里为 http
String serverName = request .getServerName();//服务器名称
int serverPort = request .getServerPort();//服务器端口
String servletPath = request.getServletPath();// servlet的路径
Principal userPrincipal = request.getUserPrincipal();
String accept = request.getHeader( "accept");//浏览器支持的格式
String referer = request.getHeader("referer" );//从哪个页面单击到本页
//user-agent 包括操作系统类型、版本号、浏览器类型、版本号
String userAgent = request.getHeader("user-agent" );
String serverInfo = this.getServletContext().getServerInfo();
PrintWriter out = response.getWriter();
out.println( "");
out.println( "");
out.println( " Request Servlet ");
out.println( " ");
out.println( " ");
out.println( "您的IP为" + remoteAddr + "，位于:空 "
+ "； 您使用" + getOS(userAgent) + "操作系统，"
+ getNavigatior( userAgent) + ",您使用 " + getLocale(locale)
+ "。
");
out.println( "服务器IP为" + localAddr + "，位于:空 "
+ "； 服务器使用" + serverPort + "端口，您的浏览器使用了，" + port
+ "端口访问本网页。
" );
out.println( "服务器软件为" + serverInfo + "服务器名称为 "
+ localName + "。
" );
out.println( "您的浏览器接受" + getAccept(accept) + "。
" );
out.println( "您从" + referer + "访问到该页面。
" );
out.println( "使用的协议为" + protocol + "。URL协议头" + scheme
+ ",服务器名称" + serverName + ",您访问的URI为"
+ requestURI + "。
" );
out.println( "该servlet的路径为" + servletPath + ", 该servlet类名为" + this.getClass().getName()
+ "。
");
out.println( "本应用程序在硬盘的根目录为" + this.getServletContext().getRealPath("" ) + ", 网络的相对路径为" + contextPath + "。
" );
out.println( "
");
out.println( "
单击刷新本页面" );
out.println( " ");
out.println( "");
out.flush();
out.close();
}
/**
* Initialization of the servlet.
*
* @throws ServletException
* if an error occurs
*/
public void init() throws ServletException {
// Put your code here
}
}
结果：
3.4.2 response生成图片验证码
通过HttpServletResponese获取的PrintWrite对象只能写字符型数据。
这里使用Servlet输出图片验证码，原理：
服务器生成一个包含随机字符串的图片发给客户端，客户端提交数据时需要填写字符串作为验证。
Servlet输出图片时，需要调用getOutputStream.
IdentityServlet.java
public class IdentityServlet extends HttpServlet {
// 随机字典 不包括男人的0，O，1，I
public static final char[] CHARS = { '2', '3', '4', '5', '6' , '7' , '8' ,
'9', 'A', 'B', 'C', 'D', 'D', 'E', 'F', 'G', 'H' , 'J' , 'K' , 'L' ,
'M', 'N', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W' , 'X' , 'Y' , 'Z' };
public static Random random = new Random();
// 获取6位随机数
public static String getRandomstring() {
StringBuffer buffer = new StringBuffer();// 字符串缓存
for (int i = 0; i < 6; i++) {
buffer.append( CHARS[random .nextInt(CHARS. length)]);
}
return buffer .toString();
}
// 获取随机的颜色
public static Color getRandomColor() {
return new Color(random.nextInt(255), random.nextInt(255),
random.nextInt(255));
}
// 返回某颜色的反色
public static Color getReverseColor(Color c ) {
return new Color(255 - c.getRed(), 255 - c.getGreen(),
255 - c.getBlue());
}
/**
* Constructor of the object.
*/
public IdentityServlet() {
super();
}
/**
* Destruction of the servlet.
*/
public void destroy() {
super.destroy(); // Just puts "destroy" string in log
// Put your code here
}
/**
* The doGet method of the servlet.
*
* This method is called when a form has its tag value method equals to get.
*
* @param request
* the request send by the client to the server
* @param response
* the response send by the server to the client
* @throws ServletException
* if an error occurred
* @throws IOException
* if an error occurred
*/
public void doGet(HttpServletRequest request , HttpServletResponse response )
throws ServletException, IOException {
response.setContentType( "image/jpeg");// 设置输出类型
String randomString = getRandomstring();
// 放到session中
request.getSession( true).setAttribute("randomString" , randomString);
// 图片高度和宽度
int width = 100;
int height = 30;
// 随机颜色 背景色
Color color = getRandomColor();
Color reverse = getReverseColor(color);
// 创建彩色图片
BufferedImage bi = new BufferedImage(width , height,
BufferedImage. TYPE_INT_RGB);
// 获取绘图对象
Graphics2D g = bi.createGraphics();
g.setFont( new Font(Font.SANS_SERIF, Font.BOLD, 16));
g.setColor( color);
g.fillRect(0, 0, width, height); // 绘制背景
g.setColor( reverse); // 设置颜色
g.drawString( randomString, 18, 20);// 绘制随机字符
for (int i = 0, n = random.nextInt(100); i < n; i++) {
g.drawRect( random.nextInt(width ), random.nextInt(height ), 1, 1);
}
ServletOutputStream out = response.getOutputStream();
JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out);
encoder.encode(bi);
out.flush();
}
/**
* The doPost method of the servlet.
*
* This method is called when a form has its tag value method equals to
* post.
*
* @param request
* the request send by the client to the server
* @param response
* the response send by the server to the client
* @throws ServletException
* if an error occurred
* @throws IOException
* if an error occurred
*/
public void doPost(HttpServletRequest request , HttpServletResponse response )
throws ServletException, IOException {
response.setContentType( "text/html");
PrintWriter out = response.getWriter();
out.println( "");
out.println( "");
out.println( " A Servlet ");
out.println( " ");
out.print( " This is ");
out.print( this.getClass());
out.println( ", using the POST method");
out.println( " ");
out.println( "");
out.flush();
out.close();
}
/**
* Initialization of the servlet.
*
* @throws ServletException
* if an error occurs
*/
public void init() throws ServletException {
// Put your code here
}
}
注意
JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out);
encoder.encode(bi);
需要导入头文件：
import com.sun.image.codec.jpeg.JPEGCodec;
import com.sun.image.codec.jpeg.JPEGImageEncoder;
生成的结果如下：
我们可以html.文件引用这个图片，identity.html
注意html中的路径问题;