Servlet从入门到精通

Servlet从入门到精通

Servlet是sun公司提供的一门用于开发动态web资源的技术。
Sun公司在其API中提供了一个servlet接口，用户若想用发一个动态web资源(即开发一个Java程序向浏览器输出数据)，需要完成以下2个步骤：
1、编写一个Java类，实现servlet接口。
2、把开发好的Java类部署到web服务器中。
按照一种约定俗成的称呼习惯，通常我们也把实现了servlet接口的java程序，称之为Servlet

Servlet程序是由WEB服务器调用，web服务器收到客户端的Servlet访问请求后：
　　①Web服务器首先检查是否已经装载并创建了该Servlet的实例对象。如果是，则直接执行第④步，否则，执行第②步。
　　②装载并创建该Servlet的一个实例对象。
　　③调用Servlet实例对象的init()方法。
　　④创建一个用于封装HTTP请求消息的HttpServletRequest对象和一个代表HTTP响应消息的HttpServletResponse对象，然后调用Servlet的service()方法并将请求和响应对象作为参数传递进去。
　　⑤WEB应用程序被停止或重新启动之前，Servlet引擎将卸载Servlet，并在卸载之前调用Servlet的destroy()方法。

Servlet接口SUN公司定义了两个默认实现类，分别为：GenericServlet、HttpServlet。
　　HttpServlet指能够处理HTTP请求的servlet，它在原有Servlet接口上添加了一些与HTTP协议处理方法，它比Servlet接口的功能更为强大。因此开发人员在编写Servlet时，通常应继承这个类，而避免直接去实现Servlet接口。
　　HttpServlet在实现Servlet接口时，覆写了service方法，该方法体内的代码会自动判断用户的请求方式，如为GET请求，则调用HttpServlet的doGet方法，如为Post请求，则调用doPost方法。因此，开发人员在编写Servlet时，通常只需要覆写doGet或doPost方法，而不要去覆写service方法。

Servlet是一个供其他Java程序（Servlet引擎）调用的Java类，它不能独立运行，它的运行完全由Servlet引擎来控制和调度。
　　针对客户端的多次Servlet请求，通常情况下，服务器只会创建一个Servlet实例对象，也就是说Servlet实例对象一旦创建，它就会驻留在内存中，为后续的其它请求服务，直至web容器退出，servlet实例对象才会销毁。
　　在Servlet的整个生命周期内，Servlet的init方法只被调用一次。而对一个Servlet的每次访问请求都导致Servlet引擎调用一次servlet的service方法。对于每次访问请求，Servlet引擎都会创建一个新的HttpServletRequest请求对象和一个新的HttpServletResponse响应对象，然后将这两个对象作为参数传递给它调用的Servlet的service()方法，service方法再根据请求方式分别调用doXXX方法。
　　如果在<servlet>元素中配置了一个<load-on-startup>元素，那么WEB应用程序在启动时，就会装载并创建Servlet的实例对象、以及调用Servlet实例对象的init()方法。
举例：
<servlet>
<servlet-name>invoker</servlet-name>
<servlet-class>
org.apache.catalina.servlets.InvokerServlet
</servlet-class>
<load-on-startup>1</load-on-startup>
</servlet>

　　用途：为web应用写一个InitServlet，这个servlet配置为启动时装载，为整个web应用创建必要的数据库表和数据。

每个servlet都有一个ServletConfig对象.用来初始化Servlet参数

配置Servlet初始化参数:在Servlet的配置文件web.xml中，可以使用一个或多个<init-param>标签为servlet配置一些初始化参数。

<servlet>
<servlet-name>servletConfigTest</servlet-name>
<servlet-class>com.demo.servlet.ServletConfigTest</servlet-class>
<init-param>
<param-name>name</param-name>
<param-value>dongyangyang</param-value>
</init-param>
<init-param>
<param-name>password</param-name>
<param-value>123456</param-value>
</init-param>
<init-param>
<param-name>charset</param-name>
<param-value>UTF-8</param-value>
</init-param>
</servlet>
<servlet-mapping>
<servlet-name>servletConfigTest</servlet-name>
<url-pattern>/servletConfig</url-pattern>
</servlet-mapping>

package com.demo.servlet;

/**
* ServletConfig演示
*/
import java.io.IOException;
import java.util.Enumeration;

import javax.servlet.ServletConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class ServletConfigTest extends HttpServlet {

private static final long serialVersionUID = 1L;

/**
* 定义ServletConfig对象来接收配置的初始化参数
*/
private ServletConfig config;

public ServletConfigTest() {
super();
}

/**
* 当servlet配置了初始化参数后，web容器在创建servlet实例对象时，
* 会自动将这些初始化参数封装到ServletConfig对象中，并在调用servlet的init方法时，
* 将ServletConfig对象传递给servlet。进而通过ServletConfig对象就可以
* 得到当前servlet的初始化参数信息。
*/
@Override
public void init(ServletConfig config) throws ServletException {
super.init(config);
this.config = config;
}

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

//---------------------ServletConfig---------------------start
//获取在web.xml中配置的初始化参数
String paramVal = this.config.getInitParameter("name");//获取指定的初始化参数
response.getWriter().print(paramVal);
//ie支持hr/,br/.火狐,谷歌不支持
response.getWriter().print("<hr/>");
//获取所有的初始化参数
Enumeration<String> e = config.getInitParameterNames();
while(e.hasMoreElements()){
String name = e.nextElement();
String value = config.getInitParameter(name);
response.getWriter().print(name + "=" + value + "<br/>");
}
//---------------------ServletConfig---------------------end

//---------------------ServletContext---------------------start
ServletContext context = this.config.getServletContext();
String data = (String)context.getAttribute("data");
response.getWriter().print( "data = " + data);
//---------------------ServletContext---------------------end
}

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
}

}

WEB容器在启动时，它会为每个WEB应用程序都创建一个对应的ServletContext对象，它代表当前web应用。
　　ServletConfig对象中维护了ServletContext对象的引用，开发人员在编写servlet时，可以通过ServletConfig.getServletContext方法获得ServletCon
13a7a
text对象。
　　由于一个WEB应用中的所有Servlet共享同一个ServletContext对象，因此Servlet对象之间可以通过ServletContext对象来实现通讯。ServletContext对象通常也被称之为context域对象。

1.多个Servlet通过ServletContext对象实现数据共享
2.获取WEB应用的初始化参数.web.xml添加:
<context-param>
<param-name>url</param-name>
<param-value>jdbc:mysql://localhost:3306/test</param-value>
</context-param>

package com.demo.servlet;

import java.io.IOException;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
* WEB容器在启动时，它会为每个WEB应用程序都创建一个对应的ServletContext对象，它代表当前web应用。
　　ServletConfig对象中维护了ServletContext对象的引用，开发人员在编写servlet时，可以通过ServletConfig.getServletContext方法获得ServletContext对象。
　　由于一个WEB应用中的所有Servlet共享同一个ServletContext对象，因此Servlet对象之间可以通过ServletContext对象来实现通讯。ServletContext对象通常也被称之为context域对象。
* @author 353654
*
*/
@WebServlet("/servletContext")
public class ServletContextTest extends HttpServlet {

private static final long serialVersionUID = 1L;

public ServletContextTest() {
super();
}

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
String data = "Hello!!!";
//根据ServletConfig对象获取ServletContext
ServletContext context = this.getServletConfig().getServletContext();
context.setAttribute("data", data);//将data存储到ServletContext对象中

//获取web容器启动的初始化参数url
String parameter = context.getInitParameter("url");
System.out.println(parameter);
response.getWriter().print("url = " + parameter);
}

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
}

}

package com.demo.servlet;

import java.io.IOException;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet("/servletForward")
public class ServletForwardTest extends HttpServlet {

private static final long serialVersionUID = 1L;

public ServletForwardTest() {
super();
}

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//      String data = "<h1><font color='red'>servletForward转发到servletForward2</font></h1>";
//      response.setCharacterEncoding("utf-8");
//      response.getOutputStream().write(data.getBytes());
//获取ServletContext对象
ServletContext context = this.getServletContext();
//获取请求转发对象(RequestDispatcher)
RequestDispatcher rd = context.getRequestDispatcher("/servletForward2");
System.out.println("servletForward转发到servletForward2");
rd.forward(request, response);//调用forward方法实现请求转发
}

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
}

}

package com.demo.servlet;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet("/servletForward2")
public class ServletForwardTest2 extends HttpServlet {

private static final long serialVersionUID = 1L;

public ServletForwardTest2() {
super();
}

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

//使用response.getOutputStream()向浏览器输出中文.不管输出字符汉字还是数字都必须输出字节数组
response.setHeader("Content-type", "text/html;charset=UTF-8");
//response.setContentType("text/html;charset=UTF-8");
response.getOutputStream().write("曹杰".getBytes("UTF-8"));//设置服务端编码集
//      response.getOutputStream().write("曹杰".getBytes());//默认工作空间编码

//使用response.getWriter()向浏览器输出中文
//      response.setHeader("content-type", "text/html;charset=UTF-8");
//      response.setCharacterEncoding("UTF-8");
//      PrintWriter out = response.getWriter();
//      //多学一招：使用HTML语言里面的<meta>标签来控制浏览器行为，模拟通过设置响应头控制浏览器行为
//      //out.write("<meta http-equiv='content-type' content='text/html;charset=UTF-8'/>");
//      out.write("曹杰");//使用PrintWriter流向客户端输出字符
}

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
}

}

package com.demo.servlet;

import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.text.MessageFormat;
import java.util.Properties;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
* 通过ServletContext对象读取资源文件
* @author 353654
*
*/
@WebServlet("/servletContextReadFile")
public class ServletContextReadFileTest extends HttpServlet {

private static final long serialVersionUID = 1L;

public ServletContextReadFileTest() {
super();
}

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
readResourceFile(response);
}

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
}

/**
* 通过ServletContext对象读取conf目录下的jdbc.properties配置文件
*/
private void readResourceFile(HttpServletResponse response) throws IOException{
/**
* getResourceAsStream()是指向webRoot/webapp目录
* 读取webRoot/webapp目录下的配置文件
* getResourceAsStream("db.properties")
* 读取src下的配置文件
* getResourceAsStream("/WEB-INF/classes/db.properties")
*/
String path = this.getServletContext().getRealPath("/WEB-INF/classes/jdbc.properties");
InputStreamReader in = new InputStreamReader(new FileInputStream(path),"utf-8");
Properties prop = new Properties();
//        InputStream in = this.getServletContext().getResourceAsStream("/WEB-INF/classes/jdbc.properties");
prop.load(in);
String driver = prop.getProperty("driver");
String url = prop.getProperty("url");
String username = prop.getProperty("username");
String password = prop.getProperty("password");
response.setContentType("text/html;charset=UTF-8");
response.getWriter().println("读取conf目录下的jdbc.properties配置文件：");
response.getWriter().println(MessageFormat.format("driver={0},url={1},username={2},password={3}",driver,url,username,password));
}
}

package com.demo.servlet;

import java.io.IOException;
import java.io.InputStream;
import java.text.MessageFormat;
import java.util.Properties;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
* 用类加载器读取资源文件
*/
@WebServlet("/classLoaderReadFile")
public class ClassLoaderReadFileTest extends HttpServlet {

private static final long serialVersionUID = 1L;

public ClassLoaderReadFileTest() {
super();
}

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
response.setHeader("content-type","text/html;charset=UTF-8");
readResourceFile(response);
}

private void readResourceFile(HttpServletResponse response) throws IOException {
//获取到装载当前类的类装载器
ClassLoader loader = ClassLoaderReadFileTest.class.getClassLoader();
//用类装载器读取src目录下的db1.properties配置文件
InputStream in = loader.getResourceAsStream("jdbc.properties");
Properties prop = new Properties();
prop.load(in);
String driver = prop.getProperty("driver");
String url = prop.getProperty("url");
String username = prop.getProperty("username");
String password = prop.getProperty("password");
response.getWriter().println("用类装载器读取src目录下的jdbc.properties配置文件：");
response.getWriter().println(
MessageFormat.format("driver={0},url={1},username={2},password={3}",
driver,url, username, password));
}

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
}

}

package com.demo.servlet;

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

@WebServlet("/servletCache")
public class ServletCacheTest extends HttpServlet {

private static final long serialVersionUID = 1L;

public ServletCacheTest() {
super();
}

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
String data = "董阳-------servlet缓存";
/**
* 设置数据合理的缓存时间值，以避免浏览器频繁向服务器发送请求，提升服务器的性能
* 这里是将数据的缓存时间设置为1天
*/
response.setHeader("content-type","text/html;charset=UTF-8");
response.setDateHeader("expires",System.currentTimeMillis() + 24 * 3600 * 1000);
response.getOutputStream().write(data.getBytes());
}

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
}

}

package com.demo.servlet;

import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.URLEncoder;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
* 下载文件功能时，要使用OutputStream流，避免使用PrintWriter流，
* 因为OutputStream流是字节流，可以处理任意类型的数据，
* 而PrintWriter流是字符流，只能处理字符数据，如果用字符流处理字节数据，会导致数据丢失。
*/
@WebServlet("/downLoad")
public class DownLoadServletTest extends HttpServlet {

private static final long serialVersionUID = 1L;

public DownLoadServletTest() {
super();
}

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
downloadFileByOutputStream(response);
}

/**
* 下载文件，通过OutputStream流
* @param response
* @throws IOException
*/
private void downloadFileByOutputStream(HttpServletResponse response) throws IOException {
//获取要下载的文件的绝对路径,读取webapp目录下download文件夹
String realPath = this.getServletContext().getRealPath("/download/董阳.JPG");
//获取要下载的文件名
String fileName = realPath.substring(realPath.lastIndexOf("\\")+1);
//设置content-disposition响应头控制浏览器以下载的形式打开文件，中文文件名要使用URLEncoder.encode方法进行编码，否则会出现文件名乱码
response.setHeader("content-disposition", "attachment;filename="+URLEncoder.encode(fileName, "UTF-8"));
InputStream in = new FileInputStream(realPath);//获取文件输入流
int len = 0;
byte[] buffer = new byte[1024];
OutputStream out = response.getOutputStream();
while ((len = in.read(buffer)) > 0) {
out.write(buffer,0,len);//将缓冲区的数据输出到客户端浏览器
}
in.close();
}

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
}

}

package com.demo.servlet;

import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.geom.QuadCurve2D;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;

import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet("/autoVerificationCode")
public class VerificationCodeServlet extends HttpServlet {

private static final long serialVersionUID = 1L;

//成员变量,不允许修改,否则有线程安全问题
private static final String[] font = { "Ravie", "Forte", "Arial", "Courier" };

private static final int[] xarr = { 23, 24, 19, 20, 21 };

private static final int[] yarr = { 20, 21, 22, 23, 24, 25, 16, 17, 18 };

private static final int[] font_size = { 28, 29, 30, 21, 22, 23, 24, 27, 26, 25 };

// 随机字体样式
private static final int[] fontStyle = { Font.HANGING_BASELINE, Font.ITALIC, Font.LAYOUT_LEFT_TO_RIGHT, Font.LAYOUT_NO_LIMIT_CONTEXT, Font.LAYOUT_NO_START_CONTEXT,
Font.LAYOUT_RIGHT_TO_LEFT, Font.CENTER_BASELINE, Font.PLAIN, Font.ROMAN_BASELINE, Font.TRUETYPE_FONT, Font.TYPE1_FONT, Font.BOLD };

private static char[] c = { 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'j', 'k', 'm', 'n', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', 'A', 'B', 'C', 'D', 'E', 'F',
'G', 'H', 'J', 'K', 'L', 'M', 'N', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', '1', '3', '5', '6', '7', '8', '9' };

public VerificationCodeServlet() {
super();
}

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doPost(request, response);
}

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
Random random = new Random();
int width = 100, height = 40;
BufferedImage bi = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
Graphics2D g = (Graphics2D) bi.getGraphics();
g.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
g.setColor(randColor(240, 255,random));
g.fillRect(0, 0, width, height);
g.drawRect(1, 1, width - 2, height - 2);
for (int i = 0; i < 10; i++) {
g.setColor(randColor(150, 250,random));
g.drawOval(random.nextInt(110), random.nextInt(24), 5 + random.nextInt(10), 5 + random.nextInt(10));
}
g.setFont(getFont());
g.setColor(randColor(xarr[(int) (Math.random() * 5)], 254 ,random));
String value = getRandom(4,random);
for (int i = 0, len = value.length(); i < len; i++) {
String rand = String.valueOf(value.charAt(i));
int degree = random.nextInt(23);
if (i % 2 == 0) {
degree = degree * (-1);
}
int x = xarr[(int) (Math.random() * 5)] * i, y = yarr[(int) (Math.random() * 8)];
g.rotate(Math.toRadians(degree), x, y);
g.setColor(randColor(48, 254,random));
g.drawString(rand, x + 8, y + 10);
g.rotate(-Math.toRadians(degree), x, y);
}
// 图片中间线
g.setColor(randColor(0, 200,random));
// width是线宽,float型
BasicStroke bs = new BasicStroke(2);
g.setStroke(bs);
// 画出曲线
QuadCurve2D.Double curve = new QuadCurve2D.Double(0d, random.nextInt(height - 8) + 4, width / 2, height / 2, width, random.nextInt(height - 8) + 4);
g.draw(curve);
// 销毁图像
g.dispose();
//将随机字符串存在session中
request.getSession().setAttribute("checkcode", value);
System.out.println(value);
//设置响应头通知浏览器以图片的形式打开
response.setContentType("image/jpeg");//等同于response.setHeader("Content-Type", "image/jpeg");
//设置响应头控制浏览器不要缓存
response.setDateHeader("expries", -1);
response.setHeader("Cache-Control", "no-cache");
response.setHeader("Pragma", "no-cache");
//自动刷新5秒一次
//response.setHeader("refresh", "5");
ImageIO.write(bi, "png", response.getOutputStream());
}

private static Font getFont() {
return new Font(font[(int) (Math.random() * 4)], fontStyle[(int) (Math.random() * 12)], font_size[(int) (Math.random() * 10)]);
}

private static Color randColor(int fc, int bc,Random random) {// 给定范围获得随机颜色
if (fc > 255) {
fc = 255;
}
if (bc > 255) {
bc = 255;
}
int r = fc + random.nextInt(bc - fc);
int g = fc + random.nextInt(bc - fc);
int b = fc + random.nextInt(bc - fc);
return new Color(r, g, b);
}

public static String getRandom(int size,Random random) {
StringBuilder sb = new StringBuilder();
for (int i = 0; i < size; i++) {
sb.append(c[Math.abs(random.nextInt()) % c.length]);
}
return sb.toString();
}
}

package com.demo.servlet;

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

@WebServlet("/redirectServlet")
public class RedirectServletTest extends HttpServlet {

private static final long serialVersionUID = 1L;

public RedirectServletTest() {
super();
}

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//1.重定向到验证码Servlet.
response.sendRedirect(request.getContextPath()+"/verificationCode"); //=="/servlet/verificationCode"

//      ${pageContext.request.contextPath} == request.getContextPath()  都是获取 /项目名称

//2.使用response设置302状态码和设置location响应头实现重定向实现请求重定向
//response.setHeader("Location", "/servlet/verificationCode");
//response.setStatus(HttpServletResponse.SC_FOUND);//设置302状态码，等同于response.setStatus(302);
}

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request,response);
}

}