Java+MyEclipse+Tomcat (四)Servlet提交表单和数据库操作

前面三篇文章讲述了如何配置MyEclipse和Tomcat开发JSP网站、如何配置Servlet简单实现表单提交、如何配置MySQL实现JSP数据库查询。
这篇文章主要讲述Servlet表单的提交、Java中实现数据库的查询操作和自己遇到的瓶颈及理解。Java Web基础性文章，希望对大家有所帮助~
  Java+MyEclipse+Tomcat (一)配置过程及jsp网站开发入门
  Java+MyEclipse+Tomcat (二)配置Servlet及简单实现表单提交
  Java+MyEclipse+Tomcat (三)配置MySQL及查询数据显示在JSP网页中
两个项目的免费下载地址(希望对你有所帮助)：
  http://download.csdn.net/detail/eastmount/8701707

一. Servlet表单提交

新建Web Project，项目名称为TestServlet01。项目结构如下图所示：

然后修改index.jsp代码如下：

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html><head><base href="<%=basePath%>"><title>My JSP 'index.jsp' starting page</title><style>body, div, td, input {font-size:18px; margin:0px; }.line {margin:2px; }</style></head><body><form action="/TestServlet01/servlet/PostServlet" method="POST"><div align="center"><br/><fieldset style='width:60%'><legend>填写用户信息</legend><br/><div class='line'><div align="left">出发地:<input type="text" id="start" name="start" style='font-size:18px' width=200/></div></div><div class='line'><div align="left">到达地:<input type="text" id="end" name="end" style='font-size:18px'/></div></div><div class='line'><br /><div align="left">请选择性别：<input type="radio" name="sex" value="男" id="sexMale"><label for="sexMale">男</label><input type="radio" name="sex" value="女" id="sexFemale"><label for="sexFemale">女</label></div></div><div class='line'><div align="left">请选择您的爱好：<input type="checkbox" name="interesting" value="音乐" id="i1"><label for="i1">音乐</label> <input type="checkbox" name="interesting" value="旅游" id="i2"><label for="i2">旅游</label> <input type="checkbox" name="interesting" value="运动" id="i3"><label for="i3">运动</label> </div></div><div class='line'><div align="left">请选择车票类型：<select name="seat"><option>---请选择乘坐类型---</option><optgroup label="卧铺"><option value="上铺">上铺</option><option value="中铺">中铺</option><option value="下铺">下铺</option></optgroup><optgroup label="其他"><option value="硬座">硬座</option><option value="软座">软座</option><option value="站票">站票</option></optgroup></select></div></div><div class='line'><br /><div align="left" class='leftDiv'>备注信息：</div><div align="left" class='rightDiv'><textarea name="description" rows="8" style="width:300px; ">请填写备注信息... </textarea></div></div><div class='line'><div align="left"><br/><input type="submit" name="Select" value="提交信息" style='font-size:18px'/><br/></div></div></fieldset>
</div>
</form>
</body>
</html>

运行效果如下图所示：

核心代码：
<form action="/TestServlet01/servlet/PostServlet" method="POST">
出发地:<input type="text" id="start" name="start" style='font-size:18px'/>
<input type="submit" name="Select" value="提交信息"/>
</form>
然后再src中右键添加Package，包名为servlet；再添加Servlet文件，文件名PostServlet.java。选择

图标。前面文章讲述过Servlet的手动配置过程，包括servlet类、映射等，现在它自动生成的WebRoot/WEB-INF/web.xml文件如下：

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="3.0" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"><display-name></display-name><servlet><description>This is the description of my J2EE component</description><display-name>This is the display name of my J2EE component</display-name><servlet-name>PostServlet</servlet-name><servlet-class>servlet.PostServlet</servlet-class></servlet><servlet-mapping><servlet-name>PostServlet</servlet-name><url-pattern>/servlet/PostServlet</url-pattern></servlet-mapping> <welcome-file-list><welcome-file>index.jsp</welcome-file></welcome-file-list>
</web-app>

同时修改src/servlet/PostServlet.java文件，采用POST方法显示表单数据：

package servlet;import java.io.IOException;
import java.io.PrintWriter;import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;public class PostServlet extends HttpServlet {public PostServlet() {super();}public void destroy() {super.destroy(); // Just puts "destroy" string in log// Put your code here}public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {response.setContentType("text/html");PrintWriter out = response.getWriter();out.println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");out.println("<HTML>");out.println("  <HEAD><TITLE>A Servlet</TITLE></HEAD>");out.println("  <BODY>");out.print("    This is ");out.print(this.getClass());out.println(", using the GET method");out.println("  </BODY>");out.println("</HTML>");out.flush();out.close();}/*** The doPost method of the servlet. <br>** 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.setCharacterEncoding("UTF-8"); //设置输出编码request.setCharacterEncoding("UTF-8");String startName = request.getParameter("start"); //获取出发地String endName = request.getParameter("end");     //获取到达地String sex = request.getParameter("sex");         //获取性别String [] interest = request.getParameterValues("interesting"); //获取兴趣String seat = request.getParameter("seat");        //获取座位String info = request.getParameter("description"); //获取备注信息response.setContentType("text/html");  //设置输出类型PrintWriter out = response.getWriter(); //获取out对象out.println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");out.println("<HTML>");out.println("  <HEAD><TITLE>A Servlet</TITLE></HEAD>");out.println("  <BODY>");out.println("<H2>出发地："+ startName +"</H2>");out.println("<H2>到达地："+ endName +"</H2>");out.println("<H2>性别："+ sex +"</H2>");out.println("<H2>兴趣");for(String str:interest) {out.println(str+" ");}out.println("</H2><H2>座位类型："+ seat +"</H2>");out.println("<H2>备注信息："+ info +"</H2>");out.println("  </BODY>");out.println("</HTML>");out.flush();out.close();}/*** Initialization of the servlet. <br>** @throws ServletException if an error occurs*/public void init() throws ServletException {// Put your code here}}

运行效果如下图所示：

二. Servlet数据库查询

还是使用上面的项目进行修改，实现Servlet数据库查询操作。数据库配置可以参照上一篇博客配置MySQL的过程，我新建数据库test01，插入表Train，表中数据如下图：

然后修改index.jsp，代码如下：

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html><head><base href="<%=basePath%>"><title>My JSP 'index.jsp' starting page</title><style>body, div, td, input {font-size:18px; margin:0px; }.line {margin:2px; }</style></head><body><form action="/TestServlet01/servlet/PostServlet" method="POST"><div align="center"><br/><fieldset style='width:60%'><legend>填写用户信息</legend><br/><div class='line'><div align="left">出发地:<input type="text" id="start" name="start" style='font-size:18px' width=200/></div></div><div class='line'><div align="left"><br/><input type="submit" name="Select" value="提交信息" style='font-size:18px'/><br/></div></div></fieldset>
</div>
</form>
</body>
</html>

修改的PostServlet.java代码如下：

package servlet;import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;public class PostServlet extends HttpServlet {//自定义变量private Connection connection = null; //定义数据库连接对象private String driverName = "com.mysql.jdbc.Driver"; //数据库驱动器private String userName = "root"; //数据库用户名private String userPasswd = "123456"; //密码private String dbName = "test01"; //数据库名称private String tableName = "Train"; //表明//连接字符串 数据库地址URL MySQL数据库端口3306private String url = "jdbc:mysql://localhost:3306/" + dbName + "?user="    + userName + "&password=" + userPasswd;//初始化方法public void init(ServletConfig config) throws ServletException{super.init(config);}public PostServlet() {super();}//处理GET请求方法public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException{response.setCharacterEncoding("UTF-8"); //设置输出编码request.setCharacterEncoding("UTF-8");response.setContentType("text/html");  //设置输出类型PrintWriter out = response.getWriter(); //获取out对象try {//数据库操作Class.forName(driverName).newInstance();connection = DriverManager.getConnection(url);Statement statement = connection.createStatement();String startName = request.getParameter("start"); //获取出发地//注意:startName需要加单引号 否则报错 ——错误：Unknown column 'BeiJing' in 'where clause'String sql = "SELECT * FROM " + tableName +" WHERE startname='" + startName+"';";if(startName=="") {sql = "SELECT * FROM " + tableName;}ResultSet rs = statement.executeQuery(sql); out.println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");out.println("<HTML>");out.println("  <HEAD><TITLE>A Servlet</TITLE></HEAD>");out.println("  <BODY>");out.println("  <fieldset style='width:60%' ><legend>搜索结果</legend><br />");out.println(" <TABLE align='center'border='1' cellspacing='1' cellpadding='1'>");out.println("        <TR><TH>车号</TH><TH>出发地</TH><TH>到达地</TH></TR>");//循环输出查询结果while(rs.next()) {out.println("      <TR><TD>" + rs.getString(1) + "</TD>");out.println("        <TD>" + rs.getString(2) + "</TD>");out.println("      <TD>" + rs.getString(3) + "</TD></TR>");}out.println("  </TABLE>");out.println("  </fieldset>");out.println("  </BODY>");out.println("</HTML>");out.flush();out.close();rs.close(); // 关闭记录集statement.close(); // 关闭声明} catch(Exception e) {System.out.println("错误："+e.getMessage());response.sendRedirect("index.jsp");}}//处理POST请求方法public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException { doGet(request,response);}//销毁方法public void destroy() {super.destroy(); // Just puts "destroy" string in logtry {connection.close(); // 关闭连接对象}catch(Exception e) {System.out.println("关闭数据库错误："+e.getMessage());}}
}

同时WebRoot/WEB-INF/web.xml文件Servlet映射都没有变化，需要在WebRoot/WEB-INF/lib中添加mysql-connector-java-5.1.15-bin.jar，否则会报错“com.mysql.jdbc.Driver错误”。
运行效果如下图所示：

写到此处我产生了一个疑问，当表单提交信息时，获取数据库的结果有两种方法：
1.第一种是上一篇博客中写到的，在JSP中通过<% ....%>调用Java代码实现连接数据库，获取MySQL表中数据并显示；
2.第二种就是这篇博客中写到的，在JSP中通过Post方法提交表单Form，在Java中通过Servlet获取请求/响应，再通过Java中out.println("<HTML>...")输出数据库中值。
就这两种方法而言，我想实现的功能是：JSP就赋值布局，显示界面；Java就负责连接数据库、数据库增删改查，处理结果再返回给JSP中显示，而不是相互嵌套的。换句话说：JSP中点击“提交”按钮，TextBox中传递出发地，Java中介绍请求，数据库查询，得到的结果再返回给JSP中显示。
那怎么实现呢？后面的文章可能会讲到。
DAO和Java Bean是对JDBC进行分层、模块化的最有效两个方法。DAO(数据库操作对象，Database Access Object)是JDBC下常用模式，DAO出现之前，操作数据库的代码与业务代码都出现在Servlet或者JSP中，不利用业务代码的分离。DAO出现后，所有与数据库相关的操作全被拿到了DAO层实现，Servlet或JSP只操作Java Bean或者DAP层，而DAO层值操作数据库。

PS：非常高兴我自己通过实际项目找到了这个难点，然后又找到了解决方法。虽然才学习Java Web一周时间，还是学到很多东西的。个人感觉DAO类似于中间件的东西吧！最后希望文章对你有所帮助，这篇文章是讲述Servlet连接MySQL数据库及表单交互之间的知识。如果文章有不足或错误的地方，还请海涵！下一篇文章讲讲Session和一个典型简单的界面布局等相关知识吧！
（By:Eastmount 2015-5-15 半夜1点 http://blog.csdn.net/eastmount/）