标签：方法 use jdbc url trace login row cte 重写
HttpServlet:
1). 是一个 Servlet, 继承自 GenericServlet. 针对于 HTTP 协议所定制.
2). 在 service() 方法中直接把 ServletReuqest 和 ServletResponse 转为 HttpServletRequest 和 HttpServletResponse.
并调用了重载的 service(HttpServletRequest, HttpServletResponse)
在 service(HttpServletRequest, HttpServletResponse) 获取了请求方式: request.getMethod(). 根据请求方式有创建了
doXxx() 方法(xxx 为具体的请求方式, 比如 doGet, doPost)
@Override
public void service(ServletRequest req, ServletResponse res)
throws ServletException, IOException {
HttpServletRequest request;
HttpServletResponse response;
try {
request = (HttpServletRequest) req;
response = (HttpServletResponse) res;
} catch (ClassCastException e) {
throw new ServletException("non-HTTP request or response");
}
service(request, response);
}
public void service(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
//1. 获取请求方式.
String method = request.getMethod();
//2. 根据请求方式再调用对应的处理方法
if("GET".equalsIgnoreCase(method)){
doGet(request, response);
}else if("POST".equalsIgnoreCase(method)){
doPost(request, response);
}
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException{
// TODO Auto-generated method stub
}
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
// TODO Auto-generated method stub
}
3). 实际开发中, 直接继承 HttpServlet, 并根据请求方式复写 doXxx() 方法即可.
4). 好处: 直接由针对性的覆盖 doXxx() 方法; 直接使用 HttpServletRequest 和 HttpServletResponse, 不再需要强转.
1. GenericServlet:
1). 是一个 Serlvet. 是 Servlet 接口和 ServletConfig 接口的实现类. 但是一个抽象类. 其中的 service 方法为抽象方法
2). 如果新建的 Servlet 程序直接继承 GenericSerlvet 会使开发更简洁.
3). 具体实现:
①. 在 GenericServlet 中声明了一个 SerlvetConfig 类型的成员变量, 在 init(ServletConfig) 方法中对其进行了初始化
②. 利用 servletConfig 成员变量的方法实现了 ServletConfig 接口的方法
③. 还定义了一个 init() 方法, 在 init(SerlvetConfig) 方法中对其进行调用, 子类可以直接覆盖 init() 在其中实现对 Servlet 的初始化.
④. 不建议直接覆盖 init(ServletConfig), 因为如果忘记编写 super.init(config); 而还是用了 SerlvetConfig 接口的方法,
则会出现空指针异常.
⑤. 新建的 init(){} 并非 Serlvet 的生命周期方法. 而 init(ServletConfig) 是生命周期相关的方法.
public abstract class GenericServlet implements Servlet, ServletConfig {
/** 以下方法为 Servlet 接口的方法 **/
@Override
public void destroy() {}
@Override
public ServletConfig getServletConfig() {
return servletConfig;
}
@Override
public String getServletInfo() {
return null;
}
private ServletConfig servletConfig;
@Override
public void init(ServletConfig arg0) throws ServletException {
this.servletConfig = arg0;
init();
}
public void init() throws ServletException{}
@Override
public abstract void service(ServletRequest arg0, ServletResponse arg1)
throws ServletException, IOException;
/** 以下方法为 ServletConfig 接口的方法 **/
@Override
public String getInitParameter(String arg0) {
return servletConfig.getInitParameter(arg0);
}
@Override
public Enumeration getInitParameterNames() {
return servletConfig.getInitParameterNames();
}
@Override
public ServletContext getServletContext() {
return servletConfig.getServletContext();
}
@Override
public String getServletName() {
return servletConfig.getServletName();
}
}
下面针对HTTP协议封装一个基类：
@Override public void service(ServletRequest request, ServletResponse response) throws ServletException, IOException { //获取请求方式是 GET 还是 POST HttpServletRequest httpServletRequest = (HttpServletRequest) request; //需要强转 不够好哦 要是封装下 String method = httpServletRequest.getMethod();
封装：
package com.atguigu.javaweb; import java.io.IOException; import javax.servlet.ServletException; import javax.servlet.ServletRequest; import javax.servlet.ServletResponse; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; /** * 针对于 HTTP 协议定义的一个 Servlet 基类 */ public class MyHttpServlet extends MyGenericServlet { @Override public void service(ServletRequest arg0, ServletResponse arg1) throws ServletException, IOException { if(arg0 instanceof HttpServletRequest){ HttpServletRequest request = (HttpServletRequest)arg0; if(arg1 instanceof HttpServletResponse){ HttpServletResponse response = (HttpServletResponse)arg1; service(request, response); } } } public void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //1. 获取请求方式. String method = request.getMethod(); //2. 根据请求方式再调用对应的处理方法 if("GET".equalsIgnoreCase(method)){ doGet(request, response); }else if("POST".equalsIgnoreCase(method)){ doPost(request, response); } } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException{ // TODO Auto-generated method stub } public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // TODO Auto-generated method stub } }
使用起来不用强转了！：
package com.atguigu.javaweb; import java.io.IOException; import java.io.PrintWriter; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; public class LoginServlet2 extends HttpServlet { /** * */ private static final long serialVersionUID = 1L; @Override public void doPost(HttpServletRequest request, HttpServletResponse response) throws IOException { // 获取请求方式是 GET 还是 POST String method = request.getMethod(); System.out.println(method); // 1. 获取请求参数: username, password String username = request.getParameter("username"); String password = request.getParameter("password"); // 2. 获取当前 WEB 应用的初始化参数: user, password. // 需要使用 ServletContext 对象. String initUser = getServletContext().getInitParameter("user"); String initPassword = getServletContext().getInitParameter("password"); PrintWriter out = response.getWriter(); // 3. 比对 // 4. 打印响应字符串. if (initUser.equals(username) && initPassword.equals(password)) { out.print("Hello: " + username); } else { out.print("Sorry: " + username); } } }
在 MySQL 数据库中创建一个 test_users 数据表, 添加 3 个字段: id, user, password. 并录入几条记录.
定义一个 login.html, 里边定义两个请求字段: user, password. 发送请求到 loginServlet
在创建一个 LoginServlet(需要继承自 HttpServlet, 并重写其 doPost 方法),
在其中获取请求的 user, password.
利用 JDBC 从 test_users 中查询有没有和页面输入的 user, password 对应的记录
SELECT count(id) FROM test_users WHERE user = ? AND password = ?
若有, 响应 Hello:xxx, 若没有, 响应 Sorry: xxx xxx 为 user.
package com.atguigu.javaweb; import java.io.IOException; import java.io.PrintWriter; import java.sql.Connection; import java.sql.DriverManager; import java.sql.PreparedStatement; import java.sql.ResultSet; import java.sql.SQLException; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; public class LoginServlet3 extends HttpServlet{ /** * */ private static final long serialVersionUID = 1L; @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { String username = req.getParameter("username"); String password = req.getParameter("password"); Connection connection = null; PreparedStatement statement = null; ResultSet resultSet = null; PrintWriter out = resp.getWriter(); try { Class.forName("com.mysql.jdbc.Driver"); String url = "jdbc:mysql:///atguigu"; String user = "root"; String password2 = "1230"; connection = DriverManager.getConnection(url, user, password2); String sql = "SELECT count(id) FROM users WHERE username = ? " + "AND password = ?"; statement = connection.prepareStatement(sql); statement.setString(1, username); statement.setString(2, password); resultSet = statement.executeQuery(); StringBuilder result = new StringBuilder(); result.append("<html>") .append(" <head>") .append(" </head>") .append("</html>"); if(resultSet.next()){ int count = resultSet.getInt(1); if(count > 0){ out.print(result.toString()); }else{ out.print("Sorry: " + username); } } } catch (Exception e) { e.printStackTrace(); } finally{ try { if(resultSet != null){ resultSet.close(); } } catch (SQLException e) { e.printStackTrace(); } try { if(statement != null){ statement.close(); } } catch (SQLException e) { e.printStackTrace(); } try { if(connection != null){ connection.close(); } } catch (SQLException e) { e.printStackTrace(); } } } }
标签：方法 use jdbc url trace login row cte 重写
原文地址：https://www.cnblogs.com/toov5/p/10045653.html
