Servlet+Jsp实现Web简单的增删改查

        从一开始的网络编程（TCP编程对Socket进行监听，到HTTP编程），现在终于可以使用强大的API进行JavaEE编程了，Servlet底层封装了各种网络协议的处理，使我们不再深陷于对协议的编程，我们只需要处理请求和返回响应就行了。这次是个简单的用Servlet类来处理对用户的简单的增删改查，我们通过对实体类与数据库的映射来将数据传送到JSP页面上进行展示。

一、Jar包的引入

        一开始使用Servlet编程时需要引入ServletAPI这个Jar包，但是我们是Web应用只需要将应用放在Tomcat服务器上运行就行了，而Tomcat里面继承了Servlet接口所以这边不再引入，我们只需要引入利于开发和调试内嵌式TomcatJar包以及Mysql的Jar包就可以：

  		<dependency>
			<groupId>org.apache.tomcat.embed</groupId>
			<artifactId>tomcat-embed-core</artifactId>
			<version>${tomcat.version}</version>
			<scope>provided</scope>
		</dependency>
		<dependency>
			<groupId>org.apache.tomcat.embed</groupId>
			<artifactId>tomcat-embed-jasper</artifactId>
			<version>${tomcat.version}</version>
			<scope>provided</scope>
		</dependency>
		<dependency>
		    <groupId>mysql</groupId>
		    <artifactId>mysql-connector-java</artifactId>
		    <version>5.1.46</version>
		</dependency>

二、Service层核心代码

这边我们使用的是纯JDBC编程啊：

public class UserService {
	public static final String url = "jdbc:mysql://127.0.0.1:3306/test";
	public static final String username = "root";
	public static final String password = "root";
	
	public User getUserById(int id) {
		try(Connection connection = DriverManager.getConnection(url, username, password)){
			try(PreparedStatement preparedStatement = connection.prepareStatement("select id, email, name, password from user where id = ?")){
				preparedStatement.setObject(1, 1);
				ResultSet rs = preparedStatement.executeQuery();
				rs.next();
				int id1 = rs.getInt("id");
				String email = rs.getString("email");
				System.out.println(email);
				String name1 = rs.getString("name");
				String password1 = rs.getString("password");
				return new User(id1, email, name1, password1);
			}
		}catch (Exception e) {
			// TODO: handle exception
			e.printStackTrace();
		}
		return null;
		
	}
	
	public List<User> getAllOrderByAsc(int begin){
		try(Connection connection = DriverManager.getConnection(url, username, password)){
			try(PreparedStatement preparedStatement = connection.prepareStatement("select id, email, name, password from user order by id asc limit ?, 5")){	
				preparedStatement.setObject(1, begin);
				ResultSet rs = preparedStatement.executeQuery();
				List<User> list = new ArrayList<User>();
				while(rs.next()) {
					int id1 = rs.getInt("id");
					String email = rs.getString("email");
					System.out.println(email);
					String name1 = rs.getString("name");
					String password1 = rs.getString("password");
					list.add(new User(id1, email, name1, password1));
				}
				return list;
				
				
			}
		}catch (Exception e) {
			// TODO: handle exception
			e.printStackTrace();
		}
		return null;
	}
	public void deleteById(int id){
		try(Connection connection = DriverManager.getConnection(url, username, password)){
			try(PreparedStatement preparedStatement = connection.prepareStatement("delete from user where id = ?")){	
				preparedStatement.setObject(1, id);
				preparedStatement.execute();
			}
		}catch (Exception e) {
			// TODO: handle exception
			e.printStackTrace();
		}
	}
}

三、Controller层设计

我们将入口返回到list进行列表的展示，然后通过点击删除等操作传入URL进行处理，处理后返回到list列表核心代码如下：

@WebServlet(urlPatterns = "/")
public class UserServlet extends HttpServlet{
	@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		UserService userService = new UserService();
		String pi = req.getParameter("begin");
		int pageinfo = 0;
		if(pi != null) {
			pageinfo = Integer.valueOf(pi);
		}
		List<User> list = userService.getAllOrderByAsc(pageinfo);
		req.setAttribute("users", list);
		req.setAttribute("begin", pageinfo);
		req.getRequestDispatcher("/WEB-INF/user.jsp").forward(req, resp);
	}
}

@WebServlet(urlPatterns = "/deleteById")
public class UserDeleteServlet extends HttpServlet{
	@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		int id = Integer.valueOf(req.getParameter("id"));
		UserService userService = new UserService();
		userService.deleteById(id);
		resp.sendRedirect("/");
	}
}

以上代码还进行了物理分页利用Sql语句在后端直接返回分页的行数。

四、JSP设计

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8" import="java.util.*"%>
<%@page import="cn.pojo.*"%>
<%List<User> users = (List<User>)request.getAttribute("users"); %>
<%int begin = (int)request.getAttribute("begin")+5; %>
<%int end = (int)request.getAttribute("begin")-5; %>
<html>
	<body>
		<h1>Welcome to my first Web !</h1>
		<table>
			<tr>
				<td>id</td>
				<td>email</td>
				<td>name</td>
				<td>password</td>
				<td>编辑</td>
				<td>删除</td>
			</tr>
			<% for(User user : users){ 
					out.print("<tr>");
					out.print("<td>" + user.id + "</td>");
					out.print("<td>" + user.email + "</td>");
					out.print("<td>" + user.name + "</td>");
					out.print("<td>" + user.password + "</td>");
					out.print("<td>" + "编辑" + "</td>");
					out.print("<td><a href = \"/deleteById?id="+ user.id +"\">" + "删除" + "</a></td>");
					out.print("</tr>");
			}
			%>
		</table>
		<p><a href = "/?begin=<%= end %>">上一页</a>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href = "/?begin=<%= begin %>">下一页</a></p>
	</body>
</html>

五、内嵌式Tomcat启动服务器

	public static void main(String[] args) throws LifecycleException {
		// TODO Tomcat start at port: 8080
		Tomcat tomcat = new Tomcat();
		tomcat.setPort(Integer.getInteger("port", 8101));
		tomcat.getConnector();
		Context context = tomcat.addWebapp("", new File("src/main/webapp").getAbsolutePath());
		WebResourceRoot resources = new StandardRoot(context);
		resources.addPreResources(
				new DirResourceSet(resources, "/WEB-INF/classes", new File("target/classes").getAbsolutePath(), "/"));
		context.setResources(resources);
		tomcat.start();
		tomcat.getServer().await();
	}