1 简述什么是重定向。
参考答案
服务器向浏览器发送一个302状态码及一个Location消息头（该消息头的值是一个地址，称之为重定向地址），浏览器收到后会立即向重定向地址发出请求。
2 实现NetCTOSS系统中的帐务帐号的增删改查功能。
参考答案
使用后缀匹配模式，将以do结尾的请求都提交到ActionServlet中，分析do前的操作请求种类，分发到不同的分支执行相应的动作。同时将JDBC以DAO和实体的形式来实现，减少分支内的重复代码。
实现本案例可以按照如下步骤进行。
步骤一：创建web工程
创建名为Servlet_03_exec的web工程，该工程的结构图如下所示：
图-1
步骤二：新建entity.Account类
新建与account表对应的实体类，属性与表字段一一对应，添加get/set方法及构造方法、toString方法。代码如下所示：
package entity;
publicclass Account {
privateint accountId;
private String realName;
private String idcardNo;
private String loginName;
private String status;
private String telephone;
publicint getAccountId() {
return accountId;
}
publicvoid setAccountId(int accountId) {
this.accountId = accountId;
}
public String getRealName() {
return realName;
}
publicvoid setRealName(String realName) {
this.realName = realName;
}
public String getIdcardNo() {
return idcardNo;
}
publicvoid setIdcardNo(String idcardNo) {
this.idcardNo = idcardNo;
}
public String getLoginName() {
return loginName;
}
publicvoid setLoginName(String loginName) {
this.loginName = loginName;
}
public String getStatus() {
return status;
}
publicvoid setStatus(String status) {
this.status = status;
}
public String getTelephone() {
return telephone;
}
publicvoid setTelephone(String telephone) {
this.telephone = telephone;
}
}
步骤三：新建dao.DBUtil公共类
用于实现数据库的连接和关闭的工具类，该类的代码如下所示：
package dao;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
/**
* JDBC管理连接的工具类，可以获取连接和关闭连接
*/
public class DBUtil {
/**
* 获取连接对象
*/
public static Connection getConnection()throws Exception{
Connection conn = null;
try {
Class.forName("oracle.jdbc.OracleDriver");
conn = DriverManager.getConnection(
"jdbc:oracle:thin:@localhost:1521:orcl", "scott", "tiger");
} catch (Exception e) {
e.printStackTrace();
throw e;
}
return conn;
}
/**
* 关闭连接对象
*/
public static void close(Connection conn) throws Exception{
if(conn!=null){
try {
conn.close();
} catch (SQLException e) {
e.printStackTrace();
throw e;
}
}
}
public static void main(String[] args) throws Exception{
System.out.println(getConnection());
}
}
步骤四：新建dao.AccountDAO类
建立针对Account实体的数据操作类DAO。该类的代码如下所示：
package dao;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.ArrayList;
import java.util.List;
import entity.Account;
/**
* Account的数据操作对象，负责Account的增删改查
*/
public class AccountDAO {
/**
* 查询所有帐务帐号信息
*/
public List<Account> findAll() throws Exception{
List<Account> accounts = new ArrayList<Account>();
Connection conn = null;
PreparedStatement stmt = null;
ResultSet rs = null;
try{
conn = DBUtil.getConnection();
stmt = conn.prepareStatement("select * from account");
rs = stmt.executeQuery();
while(rs.next()){
Account account = new Account();
int accountId = rs.getInt("account_id");
String realName = rs.getString("real_name");
String idcardNo = rs.getString("idcard_no");
String loginName = rs.getString("login_name");
String status=rs.getString("status");
String telephone = rs.getString("telephone");
account.setAccountId(accountId);
account.setRealName(realName);
account.setIdcardNo(idcardNo);
account.setLoginName(loginName);
account.setStatus(status);
account.setTelephone(telephone);
accounts.add(account);
}
}catch(Exception e){
e.printStackTrace();
throw e;
}finally{
DBUtil.close(conn);
}
return accounts;
}
/**
* 删除帐务帐号信息
*/
public void delete(int accountId) throws Exception{
Connection conn = null;
PreparedStatement stmt = null;
try{
conn = DBUtil.getConnection();
stmt = conn.prepareStatement("delete from account where account_id=?");
stmt.setInt(1, accountId);
stmt.executeUpdate();
}catch(Exception e){
e.printStackTrace();
throw e;
}finally{
DBUtil.close(conn);
}
}
/**
* 增加帐务帐号信息
*/
public void save(Account account) throws Exception{
Connection conn = null;
PreparedStatement stmt = null;
try{
conn = DBUtil.getConnection();
stmt = conn.prepareStatement("insert into account" +
"(account_id,login_name,status,real_name,idcard_no,telephone) " +
"values(account_id_seq.nextval,?,?,?,?,?)");
stmt.setString(1, account.getLoginName());
stmt.setString(2, "0");//添加创建即为开通状态
stmt.setString(3, account.getRealName());
stmt.setString(4, account.getIdcardNo());
stmt.setString(5, account.getTelephone());
stmt.executeUpdate();
}catch(Exception e){
e.printStackTrace();
throw e;
}finally{
DBUtil.close(conn);
}
}
/**
* 根据id查询员工信息
*/
public Account findById(int id) throws Exception{
Account account = null;
Connection conn = null;
PreparedStatement stmt = null;
ResultSet rs = null;
try{
conn = DBUtil.getConnection();
stmt = conn.prepareStatement("select * from account where account_id=?");
stmt.setInt(1, id);
rs = stmt.executeQuery();
if(rs.next()){
account = new Account();
int accountId = rs.getInt("account_id");
String realName = rs.getString("real_name");
String idcardNo = rs.getString("idcard_no");
String loginName = rs.getString("login_name");
String status=rs.getString("status");
String telephone = rs.getString("telephone");
account.setAccountId(accountId);
account.setRealName(realName);
account.setIdcardNo(idcardNo);
account.setLoginName(loginName);
account.setStatus(status);
account.setTelephone(telephone);
}
}catch(Exception e){
e.printStackTrace();
throw e;
}finally{
DBUtil.close(conn);
}
return account;
}
/**
* 保存修改员工信息
*/
public void modify(Account account)throws Exception{
Connection conn = null;
PreparedStatement stmt = null;
try{
conn = DBUtil.getConnection();
stmt = conn.prepareStatement("update account set login_name=?,real_name=?," +
"idcard_no=?,telephone=? where account_id=?");
stmt.setString(1, account.getLoginName());
stmt.setString(2, account.getRealName());
stmt.setString(3, account.getIdcardNo());
stmt.setString(4, account.getTelephone());
stmt.setInt(5, account.getAccountId());
stmt.executeUpdate();
}catch(Exception e){
e.printStackTrace();
throw e;
}finally{
DBUtil.close(conn);
}
}
}
步骤五：新建web.ActionServlet类
创建用于进行动作分发的ActionServlet类，通过getRequestURI获取请求资源路径，分析do前面的动作种类，执行不同的分支。代码如下所示：
package web;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.List;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import dao.AccountDAO;
import entity.Account;
public class ActionServlet extends HttpServlet {
@Override
protected void service(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException {
request.setCharacterEncoding("UTF-8");
response.setContentType("text/html;charset=UTF-8");
PrintWriter out = response.getWriter();
// 获取请求资源路径
String uri = request.getRequestURI();
// 获取请求资源路径中除应用名以外的部分
String action = uri.substring(uri.lastIndexOf("/") + 1, uri
.lastIndexOf("."));
AccountDAO dao = new AccountDAO();
if (action.equals("list")) {
try {
List<Account> accounts = dao.findAll();
out
.println("<table table border='1' cellpadding='0' cellspacing='0' width='60%'>");
out.println("<caption>帐务帐号信息列表</caption>");
out
.println("<tr><td>ID</td><td>姓名</td><td>身份证号</td><td>登录名</td>"
+ "<td>状态</td><td>手机号</td><td>操作</td></tr>");
for (Account account : accounts) {
out.println("<tr>");
String strStatus = "";
if ("1".equals(account.getStatus())) {
strStatus = "暂停";
} else if ("2".equals(account.getStatus())) {
strStatus = "删除";
} else {
strStatus = "开通";
}
out.println("<tr><td>" + account.getAccountId()
+ "</td><td>" + account.getRealName() + "</td><td>"
+ account.getIdcardNo() + "</td><td>"
+ account.getLoginName() + "</td><td>" + strStatus
+ "</td><td>" + account.getTelephone() + "</td>");
out.println("<td><a href='delete.do?accountId="
+ account.getAccountId() + "' "
+ "onclick=\"return confirm('是否确定删除"
+ account.getRealName() + "');\">删除</a>");
out.println("<a href='load.do?accountId=" + account.getAccountId()
+ "'>修改</a></td>");
out.println("</tr>");
}
out.println("</table>");
out.println("<a href='addAccount.html'>增加帐务帐号</a>");
} catch (Exception e) {
e.printStackTrace();
out.print("系统繁忙");
}
} else if (action.equals("add")) {
String realName = request.getParameter("realName");
String idcardNo = request.getParameter("idcardNo");
String loginName = request.getParameter("loginName");
String telephone = request.getParameter("telephone");
try {
Account account = new Account();
account.setRealName(realName);
account.setIdcardNo(idcardNo);
account.setLoginName(loginName);
account.setStatus("0");
account.setTelephone(telephone);
dao.save(account);
response.sendRedirect("list.do");
} catch (Exception e) {
e.printStackTrace();
out.print("系统繁忙");
}
} else if (action.equals("delete")) {
String accountId = request.getParameter("accountId");
try {
dao.delete(Integer.parseInt(accountId));
response.sendRedirect("list.do");
} catch (Exception e) {
e.printStackTrace();
out.print("系统繁忙");
}
} else if (action.equals("load")) {
String accountId = request.getParameter("accountId");
try {
Account acc = dao.findById((Integer.parseInt(accountId)));
out.println("<html><head></head><body style='font-size:30px'>");
if (acc != null) {
out.println("<form action='modify.do' method='post'>");
out.println("编号:" + acc.getAccountId() + "<br>");
out.println("<input type='hidden' name='accountId' value='"
+ acc.getAccountId() + "'/><br>");
out.println("姓名:<input name='realName' value='"
+ acc.getRealName() + "'/><br>");
out.println("身份证:<input name='idcardNo' value='"
+ acc.getIdcardNo() + "'/><br>");
out.println("登录名:<input name='loginName' value='"
+ acc.getLoginName() + "'/><br>");
out.println("手机号:<input name='telephone' value='"
+ acc.getTelephone() + "'/><br>");
out.println("<input type='submit' value='修改'/>");
out.println("</form>");
}
out.println("</body></html>");
} catch (Exception e) {
e.printStackTrace();
out.print("系统繁忙");
}
} else if (action.equals("modify")) {
String accountId = request.getParameter("accountId");
String realName = request.getParameter("realName");
String idcardNo = request.getParameter("idcardNo");
String loginName = request.getParameter("loginName");
String telephone = request.getParameter("telephone");
try {
Account account = new Account();
account.setAccountId(Integer.parseInt(accountId));
account.setRealName(realName);
account.setIdcardNo(idcardNo);
account.setLoginName(loginName);
account.setTelephone(telephone);
dao.modify(account);
response.sendRedirect("list.do");
} catch (Exception e) {
e.printStackTrace();
out.print("系统繁忙");
}
}
out.close();
}
}
步骤六：新建addAccount.html文件
新建用于完成增加员工的表单页面。表单的action地址为ActionServlet对应的add.do，method方式为post，代码如下所示：
<html> <head> <meta http-equiv="content-type" content="text/html;charset=utf-8"> </head> <body style="font-size:24px"> <form action="add.do" method="post"> <fieldset> <legend>添加帐务帐号</legend> 姓名：<input name="realName"/><br> 身份证：<input name="idcardNo"/><br> 登录名：<input name="loginName"/><br> 手机号：<input name="telephone"/><br> <input type="submit" value="添加"/> </fieldset> </form> </body> </html>
步骤七：修改web.xml文件
使用后缀匹配模式配置ActionServlet的映射原则。代码如下所示：
<?xml version="1.0" encoding="UTF-8"?> <web-app version="2.5" 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_2_5.xsd"> <servlet> <servlet-name>actionServlet</servlet-name> <servlet-class>web.ActionServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>actionServlet</servlet-name> <url-pattern>*.do</url-pattern> </servlet-mapping> </web-app>
步骤八：部署应用，访问
部署并访问工程，访问地址为“http://localhost:8080/应用名/list.do”。
本案例的完整代码如下。
Account类的完整代码如下所示：
package entity;
publicclass Account {
privateint accountId;
private String realName;
private String idcardNo;
private String loginName;
private String status;
private String telephone;
publicint getAccountId() {
return accountId;
}
publicvoid setAccountId(int accountId) {
this.accountId = accountId;
}
public String getRealName() {
return realName;
}
publicvoid setRealName(String realName) {
this.realName = realName;
}
public String getIdcardNo() {
return idcardNo;
}
publicvoid setIdcardNo(String idcardNo) {
this.idcardNo = idcardNo;
}
public String getLoginName() {
return loginName;
}
publicvoid setLoginName(String loginName) {
this.loginName = loginName;
}
public String getStatus() {
return status;
}
publicvoid setStatus(String status) {
this.status = status;
}
public String getTelephone() {
return telephone;
}
publicvoid setTelephone(String telephone) {
this.telephone = telephone;
}
}
DBUtil类的完整代码如下所示：：
package dao;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
/**
* JDBC管理连接的工具类，可以获取连接和关闭连接
*/
public class DBUtil {
/**
* 获取连接对象
*/
public static Connection getConnection()throws Exception{
Connection conn = null;
try {
Class.forName("oracle.jdbc.OracleDriver");
conn = DriverManager.getConnection(
"jdbc:oracle:thin:@localhost:1521:orcl", "scott", "tiger");
} catch (Exception e) {
e.printStackTrace();
throw e;
}
return conn;
}
/**
* 关闭连接对象
*/
public static void close(Connection conn) throws Exception{
if(conn!=null){
try {
conn.close();
} catch (SQLException e) {
e.printStackTrace();
throw e;
}
}
}
public static void main(String[] args) throws Exception{
System.out.println(getConnection());
}
}
AccountDAO类的完整代码如下所示：
package dao;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.ArrayList;
import java.util.List;
import entity.Account;
/**
* Account的数据操作对象，负责Account的增删改查
*/
public class AccountDAO {
/**
* 查询所有帐务帐号信息
*/
public List<Account> findAll() throws Exception{
List<Account> accounts = new ArrayList<Account>();
Connection conn = null;
PreparedStatement stmt = null;
ResultSet rs = null;
try{
conn = DBUtil.getConnection();
stmt = conn.prepareStatement("select * from account");
rs = stmt.executeQuery();
while(rs.next()){
Account account = new Account();
int accountId = rs.getInt("account_id");
String realName = rs.getString("real_name");
String idcardNo = rs.getString("idcard_no");
String loginName = rs.getString("login_name");
String status=rs.getString("status");
String telephone = rs.getString("telephone");
account.setAccountId(accountId);
account.setRealName(realName);
account.setIdcardNo(idcardNo);
account.setLoginName(loginName);
account.setStatus(status);
account.setTelephone(telephone);
accounts.add(account);
}
}catch(Exception e){
e.printStackTrace();
throw e;
}finally{
DBUtil.close(conn);
}
return accounts;
}
/**
* 删除帐务帐号信息
*/
public void delete(int accountId) throws Exception{
Connection conn = null;
PreparedStatement stmt = null;
try{
conn = DBUtil.getConnection();
stmt = conn.prepareStatement("delete from account where account_id=?");
stmt.setInt(1, accountId);
stmt.executeUpdate();
}catch(Exception e){
e.printStackTrace();
throw e;
}finally{
DBUtil.close(conn);
}
}
/**
* 增加帐务帐号信息
*/
public void save(Account account) throws Exception{
Connection conn = null;
PreparedStatement stmt = null;
try{
conn = DBUtil.getConnection();
stmt = conn.prepareStatement("insert into account" +
"(account_id,login_name,status,real_name,idcard_no,telephone) " +
"values(account_id_seq.nextval,?,?,?,?,?)");
stmt.setString(1, account.getLoginName());
stmt.setString(2, "0");//添加创建即为开通状态
stmt.setString(3, account.getRealName());
stmt.setString(4, account.getIdcardNo());
stmt.setString(5, account.getTelephone());
stmt.executeUpdate();
}catch(Exception e){
e.printStackTrace();
throw e;
}finally{
DBUtil.close(conn);
}
}
/**
* 根据id查询员工信息
*/
public Account findById(int id) throws Exception{
Account account = null;
Connection conn = null;
PreparedStatement stmt = null;
ResultSet rs = null;
try{
conn = DBUtil.getConnection();
stmt = conn.prepareStatement("select * from account where account_id=?");
stmt.setInt(1, id);
rs = stmt.executeQuery();
if(rs.next()){
account = new Account();
int accountId = rs.getInt("account_id");
String realName = rs.getString("real_name");
String idcardNo = rs.getString("idcard_no");
String loginName = rs.getString("login_name");
String status=rs.getString("status");
String telephone = rs.getString("telephone");
account.setAccountId(accountId);
account.setRealName(realName);
account.setIdcardNo(idcardNo);
account.setLoginName(loginName);
account.setStatus(status);
account.setTelephone(telephone);
}
}catch(Exception e){
e.printStackTrace();
throw e;
}finally{
DBUtil.close(conn);
}
return account;
}
/**
* 保存修改员工信息
*/
public void modify(Account account)throws Exception{
Connection conn = null;
PreparedStatement stmt = null;
try{
conn = DBUtil.getConnection();
stmt = conn.prepareStatement("update account set login_name=?,real_name=?," +
"idcard_no=?,telephone=? where account_id=?");
stmt.setString(1, account.getLoginName());
stmt.setString(2, account.getRealName());
stmt.setString(3, account.getIdcardNo());
stmt.setString(4, account.getTelephone());
stmt.setInt(5, account.getAccountId());
stmt.executeUpdate();
}catch(Exception e){
e.printStackTrace();
throw e;
}finally{
DBUtil.close(conn);
}
}
}
ActionServlet类的完整代码如下所示：
package web;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.List;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import dao.AccountDAO;
import entity.Account;
public class ActionServlet extends HttpServlet {
@Override
protected void service(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException {
request.setCharacterEncoding("UTF-8");
response.setContentType("text/html;charset=UTF-8");
PrintWriter out = response.getWriter();
// 获取请求资源路径
String uri = request.getRequestURI();
// 获取请求资源路径中除应用名以外的部分
String action = uri.substring(uri.lastIndexOf("/") + 1, uri
.lastIndexOf("."));
AccountDAO dao = new AccountDAO();
if (action.equals("list")) {
try {
List<Account> accounts = dao.findAll();
out
.println("<table table border='1' cellpadding='0' cellspacing='0' width='60%'>");
out.println("<caption>帐务帐号信息列表</caption>");
out
.println("<tr><td>ID</td><td>姓名</td><td>身份证号</td><td>登录名</td>"
+ "<td>状态</td><td>手机号</td><td>操作</td></tr>");
for (Account account : accounts) {
out.println("<tr>");
String strStatus = "";
if ("1".equals(account.getStatus())) {
strStatus = "暂停";
} else if ("2".equals(account.getStatus())) {
strStatus = "删除";
} else {
strStatus = "开通";
}
out.println("<tr><td>" + account.getAccountId()
+ "</td><td>" + account.getRealName() + "</td><td>"
+ account.getIdcardNo() + "</td><td>"
+ account.getLoginName() + "</td><td>" + strStatus
+ "</td><td>" + account.getTelephone() + "</td>");
out.println("<td><a href='delete.do?accountId="
+ account.getAccountId() + "' "
+ "onclick=\"return confirm('是否确定删除"
+ account.getRealName() + "');\">删除</a>");
out.println("<a href='load.do?accountId=" + account.getAccountId()
+ "'>修改</a></td>");
out.println("</tr>");
}
out.println("</table>");
out.println("<a href='addAccount.html'>增加帐务帐号</a>");
} catch (Exception e) {
e.printStackTrace();
out.print("系统繁忙");
}
} else if (action.equals("add")) {
String realName = request.getParameter("realName");
String idcardNo = request.getParameter("idcardNo");
String loginName = request.getParameter("loginName");
String telephone = request.getParameter("telephone");
try {
Account account = new Account();
account.setRealName(realName);
account.setIdcardNo(idcardNo);
account.setLoginName(loginName);
account.setStatus("0");
account.setTelephone(telephone);
dao.save(account);
response.sendRedirect("list.do");
} catch (Exception e) {
e.printStackTrace();
out.print("系统繁忙");
}
} else if (action.equals("delete")) {
String accountId = request.getParameter("accountId");
try {
dao.delete(Integer.parseInt(accountId));
response.sendRedirect("list.do");
} catch (Exception e) {
e.printStackTrace();
out.print("系统繁忙");
}
} else if (action.equals("load")) {
String accountId = request.getParameter("accountId");
try {
Account acc = dao.findById((Integer.parseInt(accountId)));
out.println("<html><head></head><body style='font-size:30px'>");
if (acc != null) {
out.println("<form action='modify.do' method='post'>");
out.println("编号:" + acc.getAccountId() + "<br>");
out.println("<input type='hidden' name='accountId' value='"
+ acc.getAccountId() + "'/><br>");
out.println("姓 名:<input name='realName' value='"
+ acc.getRealName() + "'/><br>");
out.println("身份证:<input name='idcardNo' value='"
+ acc.getIdcardNo() + "'/><br>");
out.println("登录名:<input name='loginName' value='"
+ acc.getLoginName() + "'/><br>");
out.println("手机号:<input name='telephone' value='"
+ acc.getTelephone() + "'/><br>");
out.println("<input type='submit' value='修改'/>");
out.println("</form>");
}
out.println("</body></html>");
} catch (Exception e) {
e.printStackTrace();
out.print("系统繁忙");
}
} else if (action.equals("modify")) {
String accountId = request.getParameter("accountId");
String realName = request.getParameter("realName");
String idcardNo = request.getParameter("idcardNo");
String loginName = request.getParameter("loginName");
String telephone = request.getParameter("telephone");
try {
Account account = new Account();
account.setAccountId(Integer.parseInt(accountId));
account.setRealName(realName);
account.setIdcardNo(idcardNo);
account.setLoginName(loginName);
account.setTelephone(telephone);
dao.modify(account);
response.sendRedirect("list.do");
} catch (Exception e) {
e.printStackTrace();
out.print("系统繁忙");
}
}
out.close();
}
}
addAccount.html文件的代码如下所示：
<html> <head> <meta http-equiv="content-type" content="text/html;charset=utf-8"> </head> <body style="font-size:24px"> <form action="add.do" method="post"> <fieldset> <legend>添加帐务帐号</legend> 姓 名：<input name="realName"/><br> 身份证：<input name="idcardNo"/><br> 登录名：<input name="loginName"/><br> 手机号：<input name="telephone"/><br> <input type="submit" value="添加"/> </fieldset> </form> </body> </html>
web.xml文件的配置代码如下所示：
<?xml version="1.0" encoding="UTF-8"?> <web-app version="2.5" 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_2_5.xsd"> <servlet> <servlet-name>actionServlet</servlet-name> <servlet-class>web.ActionServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>actionServlet</servlet-name> <url-pattern>*.do</url-pattern> </servlet-mapping> </web-app>
3 简述URI和URL 的区别， 如何获取 ?
参考答案
URI，是uniform resource identifier，统一资源标识符，用来唯一的标识一个资源。而URL是uniform resource locator，统一资源定位器，它是一种具体的URI，即URL可以用来标识一个资源，而且还指明了如何定位这个资源。
在Java的URI中，一个URI实例可以代表绝对的，也可以是相对的，只要它符合URI的语法规则。而URL类则不仅符合语义，还包含了定位该资源的信息，因此它不能是相对的。从HttpServletRequest的javadoc中可以看出，getRequestURI方法返回一个String，比如请求为“POST /some/path.html?a=b HTTP/1.1”，则该方法返回的值为”/some/path.html”。而getRequestURL返回一个StringBuffer，是完整的请求资源路径，不包括querystring。
4 Servlet生命周期分哪几个阶段?什么时候执行?
参考答案
Servlet生命周期分为四个阶段，依次是实例化、初始化、就绪以及销毁。
- 阶段一：实例化。
容器调用Servlet的构造器，创建一个Servlet对象。容器创建Servlet对象的时机有以下两种情形：
情形1，开始容器里面没有Servlet对象，只有收到请求后才会创建Servlet对象。
情形2，容器启动之后就立即创建相应的实例。
- 阶段二：初始化
容器在创建好Servlet对象之后，会立即调用该对象的init方法。该方法只会执行一次。一般情况下，我们不用写init方法，因为GenericServlet已经提供了init方法的实现(将容器传递过来的ServletConfig对象保存下来，并且，提供了getServletConfig方法来获得ServletConfig对象)。
- 阶段三：就绪
容器收到请求之后调用Servlet对象的service方法来处理请求。
- 阶段四：销毁
容器依据自身的算法删除Servlet对象，删除前会调用destroy方法。该方法只会执行一次。可以重写destroy方法来实现自己的处理逻辑。
5 如何配置Servlet的初始参数,以及如何获取该初始参数?
参考答案
在web.xml文件中配置初始化参数，代码如下：
<init-param> <param-name>company</param-name> <param-value>北京达内</param-value> </init-param>
可以通过ServletConfig的getInitParameter方法获取初始化参数的值：
String company=config.getInitParameter("company")；
上述代码中，config是ServletConfig的引用。上述代码可以获取初始化参数company的值。
6 简述什么是Servlet上下文。
参考答案
容器启动之后，会为每一个Web应用创建唯一的一个符合ServletContext接口要求的对象，该对象就是servlet上下文。
7 Servlet是否是线程安全的,如何解决?
参考答案
Servlet存在线程安全问题。容器搜到请求之后，会启动一个线程来进行相应的处理。
默认情况下，容器只会为某个Servlet创建一个实例，如果同时有多个请求同时访问某个Servlet则肯定会有多个线程访问同一个Servlet实例。如果这些线程要修改Servlet实例的某个属性，就有可能发生线程安全问题。
可以使用synchronized对代码加锁来解决Servlet的安全问题。