java复习MVC

what?
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- dao
- servlet
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what?

MVC是一种分层的设计模式,结合Serlvet和JSP进行数据的显示，就是一种MVC的思想。
M 代表模型（Model） V 代表视图（View） C 代表控制器（controller)
模型是什么呢？模型就是数据，就是dao,bean
视图是什么呢？就是网页, JSP，用来展示模型中的数据
控制器是什么？控制器用来把不同的数据，显示在不同的视图上。

分页

dao

package dao;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.List;

import bean.Hero;

public class HeroDAO {

	public int getTotal() {
		int total = 0;
		try {
			Class.forName("com.mysql.jdbc.Driver");

			Connection c = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/how2java?characterEncoding=UTF-8",
					"root", "admin");

			Statement s = c.createStatement();

			String sql = "select count(*) from hero";

			ResultSet rs = s.executeQuery(sql);
			while (rs.next()) {
				total = rs.getInt(1);
			}

			System.out.println("total:" + total);

			s.close();

			c.close();

		} catch (ClassNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (SQLException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		return total;
	}

	public void add(Hero hero) {

		try {
			Class.forName("com.mysql.jdbc.Driver");

			Connection c = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/how2java?characterEncoding=UTF-8",
					"root", "admin");

			String sql = "insert into hero values(null,?,?,?)";
			PreparedStatement ps = c.prepareStatement(sql);
			ps.setString(1, hero.name);
			ps.setFloat(2, hero.hp);
			ps.setInt(3, hero.damage);

			ps.execute();

			ResultSet rs = ps.getGeneratedKeys();
			if (rs.next()) {
				int id = rs.getInt(1);
				hero.id = id;
			}

			ps.close();

			c.close();

		} catch (ClassNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (SQLException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}

	public void update(Hero hero) {
		try {
			Class.forName("com.mysql.jdbc.Driver");

			Connection c = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/how2java?characterEncoding=UTF-8",
					"root", "admin");

			String sql = "update hero set name= ?, hp = ? , damage = ? where id = ?";
			PreparedStatement ps = c.prepareStatement(sql);
			ps.setString(1, hero.name);
			ps.setFloat(2, hero.hp);
			ps.setInt(3, hero.damage);
			ps.setInt(4, hero.id);

			ps.execute();

			ps.close();

			c.close();

		} catch (ClassNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (SQLException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}

	}

	public void delete(int id) {
		try {
			Class.forName("com.mysql.jdbc.Driver");

			Connection c = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/how2java?characterEncoding=UTF-8",
					"root", "admin");

			Statement s = c.createStatement();

			String sql = "delete from hero where id = " + id;

			s.execute(sql);

			s.close();

			c.close();

		} catch (ClassNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (SQLException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}

	public Hero get(int id) {
		Hero hero = null;
		try {
			Class.forName("com.mysql.jdbc.Driver");

			Connection c = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/how2java?characterEncoding=UTF-8",
					"root", "admin");

			Statement s = c.createStatement();

			String sql = "select * from hero where id = " + id;

			ResultSet rs = s.executeQuery(sql);

			if (rs.next()) {
				hero = new Hero();
				String name = rs.getString(2);
				float hp = rs.getFloat("hp");
				int damage = rs.getInt(4);
				hero.name = name;
				hero.hp = hp;
				hero.damage = damage;
				hero.id = id;
			}

			s.close();

			c.close();

		} catch (ClassNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (SQLException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		return hero;
	}

	public List<Hero> list() {
		return list(0, Short.MAX_VALUE);
	}

	public List<Hero> list(int start, int count) {
		List<Hero> heros = new ArrayList<Hero>();

		try {
			Class.forName("com.mysql.jdbc.Driver");

			Connection c = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/how2java?characterEncoding=UTF-8",
					"root", "admin");

			String sql = "select * from hero order by id desc limit ?,? ";

			PreparedStatement ps = c.prepareStatement(sql);
			ps.setInt(1, start);
			ps.setInt(2, count);

			ResultSet rs = ps.executeQuery();

			while (rs.next()) {
				Hero hero = new Hero();
				int id = rs.getInt(1);
				String name = rs.getString(2);
				float hp = rs.getFloat("hp");
				int damage = rs.getInt(4);
				hero.id = id;
				hero.name = name;
				hero.hp = hp;
				hero.damage = damage;
				heros.add(hero);
			}

			ps.close();

			c.close();

		} catch (ClassNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (SQLException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		return heros;
	}

}

servlet

package servlet;

import java.io.IOException;
import java.util.List;

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

import bean.Hero;
import dao.HeroDAO;

public class HeroListServlet extends HttpServlet {

	protected void service(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		response.setContentType("text/html; charset=UTF-8");

		int start = 0;
		int count = 5;

		try {
			start = Integer.parseInt(request.getParameter("start"));
		} catch (NumberFormatException e) {
			// 当浏览器没有传参数start时
		}

		int next = start + count;
		int pre = start - count;

		int total = new HeroDAO().getTotal();

		int last;
		if (0 == total % count)
			last = total - count;
		else
			last = total - total % count;

		pre = pre < 0 ? 0 : pre;
		next = next > last ? last : next;

		request.setAttribute("next", next);
		request.setAttribute("pre", pre);
		request.setAttribute("last", last);

		List<Hero> heros = new HeroDAO().list(start, count);
		request.setAttribute("heros", heros);

		request.getRequestDispatcher("listHero.jsp").forward(request, response);

	}
}

<%@ page language="java" contentType="text/html; charset=UTF-8"
	pageEncoding="UTF-8" import="java.util.*"%>

<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>

<table align='center' border='1' cellspacing='0'>
	<tr>
		<td>id</td>
		<td>name</td>
		<td>hp</td>
		<td>damage</td>
		<td>edit</td>
		<td>delete</td>
	</tr>
	<c:forEach items="${heros}" var="hero" varStatus="st">
		<tr>
			<td>${hero.id}</td>
			<td>${hero.name}</td>
			<td>${hero.hp}</td>
			<td>${hero.damage}</td>
			<td><a href="editHero?id=${hero.id}">edit</a></td>
			<td><a href="deleteHero?id=${hero.id}">delete</a></td>
		</tr>
	</c:forEach>
	<tr>
		<td colspan="6" align="center">
			<a href="?start=0">[首  页]</a>
			<a href="?start=${pre}">[上一页]</a>
			<a href="?start=${next}">[下一页]</a>
			<a href="?start=${last}">[末  页]</a>
		</td>
	</tr>
</table>

如果用户登陆过了，访问listHero，就让用户正常访问，否则就跳转到登陆界面。
这是非常常见的场景，通过使用 session 来实现这个功能。
在处理登录的loginServlet 中使用将用户名保存在session中。
在HeroListServlet 中查看session中是否为空。如果为空，就表示用户没有登陆过，就跳转到登陆页面

import java.io.IOException;

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

public class LoginServlet extends HttpServlet {

	private static final long serialVersionUID = 1L;

	protected void service(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		String name = request.getParameter("name");
		String password = request.getParameter("password");

		if ("admin".equals(name) && "123".equals(password)) {
			request.getSession().setAttribute("userName", name);
			response.sendRedirect("listHero");
		} else {
			response.sendRedirect("login.html");
		}

	}
}

package servlet;

import java.io.IOException;
import java.util.List;

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

import bean.Hero;
import dao.HeroDAO;

public class HeroListServlet extends HttpServlet {

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

		String userName = (String) request.getSession().getAttribute("userName");
		if (null == userName) {
			response.sendRedirect("login.html");
			return;
		}

		int start = 0;
		int count = 5;

		try {
			start = Integer.parseInt(request.getParameter("start"));
		} catch (NumberFormatException e) {
			// 当浏览器没有传参数start时
		}

		int next = start + count;
		int pre = start - count;

		int total = new HeroDAO().getTotal();

		int last;
		if (0 == total % count)
			last = total - count;
		else
			last = total - total % count;

		pre = pre < 0 ? 0 : pre;
		next = next > last ? last : next;

		request.setAttribute("next", next);
		request.setAttribute("pre", pre);
		request.setAttribute("last", last);

		List<Hero> heros = new HeroDAO().list(start, count);
		request.setAttribute("heros", heros);

		request.getRequestDispatcher("listHero.jsp").forward(request, response);

	}
}

本文章参考自：http://how2j.cn

java复习MVC

what?

分页

dao

servlet

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