前言
很久以前便决定学习java了，那个时候还不知道J2EE到底是什么。逐渐地走了很远，才发现曾经遇到的、复现的java网站和赛题都只是一知半解。现如今总算是半只脚迈入了javaweb的大门，将成果分享一下，以供后来者参考。
注意：纯servlet项目和jsp项目有一定区别，后续学习若有成果会再次分享。
在此之前
说在前面，想要掌握CURD的基本知识需要一定基础，有关java的集合框架；servlet的部署、调用、request（response）方法；eclipse部署等要有一定了解（相信参考这篇文章学习的你已经掌握了上述知识）。
一，概述
Java2平台包括：标准版（J2SE）、企业版（J2EE）和微缩版（J2ME）三个版。
简而言之，j2EE是一种网站开发标准或者说接口。
二、CURD
备注：表格结构
mysql安装的示例类。这里把city和countrylanguage的外键都删除了，然后为country表新增了一个id列，保留了Name、SurfaceArea、Population这三个字段（String,int,float各一个），其他全部删除。
1介绍
CRUD是常见的页面功能，即我们常说的增删改查
C - Creation 增加
R - Retrieve 查询
U - Update 修改
D - DELETE 删除
备注：实体类一般定义在bean包中，DAO类一般定义在dao包中，Servlet一般定义在servlet包中，便于管理。
2查询并列表显示
准备实体类country
country表有Code、Name、Continent、Region、SurfaceArea、IndepYear、Population、LifeExpectancy、GNP、GNPOld、LocalName、GovernmentForm、HeadOfState、Capital、Code2等列名。
选择name、surfacearea、population三个（string、float、int各一个）作为country类的属性
并且为每一个属性提供public的getter和setter。
package world;
public class country {
public int id;
public String name;
public float surfacearea;
public int population;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public float getsurfacearea() {
return surfacearea;
}
public void setsurfacearea(float surfacearea) {
this.surfacearea = surfacearea;
}
public int getpopulation() {
return population;
}
public void setpopulation(int population) {
this.population = population;
}
}
准备一个CountryDAO，提供增加，删除，修改，查询等常规数据库操作方法
注意，查表的结果与字段顺序有关，若表结构更换，以下获取字段的序号都要更换。
package world;
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 world.country;
public class countrydao {
public countrydao() {
try {
Class.forName("com.mysql.jdbc.Driver");
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
}
public Connection getConnection() throws SQLException {
return DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/world?characterEncoding=UTF-8", "root","123456");
}
public int getTotal() {
int total = 0;
try (Connection c = getConnection(); Statement s = c.createStatement();) {
String sql = "select count(*) from country";
ResultSet rs = s.executeQuery(sql);
while (rs.next()) {
total = rs.getInt(1);
}
System.out.println("total:" + total);
} catch (SQLException e) {
e.printStackTrace();
}
return total;
}
public void add(country country) {
String sql = "insert into country values(null,?,?,?)";
try (Connection c = getConnection(); PreparedStatement ps = c.prepareStatement(sql);) {
ps.setString(1, country.name);
ps.setFloat(2, country.surfacearea);
ps.setInt(3, country.population);
ps.execute();
ResultSet rs = ps.getGeneratedKeys();
if (rs.next()) {
int id = rs.getInt(1);
country.id = id;
}
} catch (SQLException e) {
e.printStackTrace();
}
}
public void update(country country) {
String sql = "update country set name= ?, surfacearea = ? , population = ? where id = ?";
try (Connection c = getConnection(); PreparedStatement ps = c.prepareStatement(sql);) {
ps.setString(1, country.name);
ps.setFloat(2, country.surfacearea);
ps.setInt(3, country.population);
ps.setInt(4, country.id);
ps.execute();
} catch (SQLException e) {
e.printStackTrace();
}
}
public void delete(int id) {
try (Connection c = getConnection(); Statement s = c.createStatement();) {
String sql = "delete from country where id = " + id;
s.execute(sql);
} catch (SQLException e) {
e.printStackTrace();
}
}
public country get(int id) {
//返回值为country类的get方法
country country = null;
try (Connection c = getConnection(); Statement s = c.createStatement();) {
String sql = "select * from country where id = " + id;
ResultSet rs = s.executeQuery(sql);
if (rs.next()) {
country = new country();
String name = rs.getString(2);//获取表的第3个列名
float surfacearea = rs.getFloat("surfacearea");
int population = rs.getInt(4);//获取表的第8个列名
country.name = name;
country.surfacearea = surfacearea;
country.population = population;
country.id = id;
}
} catch (SQLException e) {
e.printStackTrace();
}
return country;
}
public List<country> list() {
return list(0, Short.MAX_VALUE);
}
public List<country> list(int start, int count) {
List<country> countries = new ArrayList<country>();
String sql = "select * from country order by id desc limit ?,? ";
try (Connection c = getConnection(); PreparedStatement ps = c.prepareStatement(sql);) {
ps.setInt(1, start);
ps.setInt(2, count);
ResultSet rs = ps.executeQuery();
while (rs.next()) {
country country = new country();
int id = rs.getInt(1);
String name = rs.getString(2);
float surfacearea = rs.getFloat("surfacearea");
int population = rs.getInt(4);
country.id = id;
country.name = name;
country.surfacearea = surfacearea;
country.population = population;
countries.add(country);
}
} catch (SQLException e) {
e.printStackTrace();
}
return countries;
}
}
编写 CountryListServlet
做一个Country的维护页面需要一些通用的操作，比如增加，删除，编辑，修改，查询等。
每个不同的操作，都需要一个对应的Servlet，除了做Country之外，还会做到其他的一些表的相关操作，所以好的规范会对将来的维护更有好处。
一般会这样命名，以查询为例 CountryListServlet ： [表][行为]Servlet 这样一种命名规则。
所以对于Country而言就会如此命名：
增加 CountryAddServlet
删除 CountryDeleteServlet
编辑 CountryEditServlet
修改 CountryUpdateServlet
查询 CountryListServlet
在CountryListServlet中，会使用CountryDAO把数据查询出来，然后拼接成一个table用于显示其内容
package world;
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 world.country;
import world.countrydao;
public class CountryListServlet extends HttpServlet {
protected void service(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html; charset=UTF-8");
List<country> countries = new countrydao().list();
StringBuffer sb = new StringBuffer();
sb.append("<table align='center' border='1' cellspacing='0'>\r\n");
sb.append("<tr><td>id</td><td>name</td><td>surfacearea</td><td>population</td></tr>\r\n");
String trFormat = "<tr><td>%d</td><td>%s</td><td>%f</td><td>%d</td></tr>\r\n";
for (country country : countries) {
String tr = String.format(trFormat, country.getId(), country.getName(), country.getsurfacearea(), country.getpopulation());
sb.append(tr);
}
sb.append("</table>");
response.getWriter().write(sb.toString());
}
}
配置web.xml
在web.xml中把路径 listHero映射到HeroListServlet上。
<?xml version="1.0" encoding="UTF-8"?>
<web-app>
<servlet>
<servlet-name>HelloServlet</servlet-name>
<servlet-class>HelloServlet</servlet-class>
<load-on-startup>10</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>HelloServlet</servlet-name>
<url-pattern>/hello</url-pattern>
</servlet-mapping>
<servlet>
<servlet-name>LoginServlet</servlet-name>
<servlet-class>LoginServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>LoginServlet</servlet-name>
<url-pattern>/login</url-pattern>
</servlet-mapping>
<servlet>
<servlet-name>RegisterServlet</servlet-name>
<servlet-class>RegisterServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>RegisterServlet</servlet-name>
<url-pattern>/register</url-pattern>
</servlet-mapping>
<servlet>
<servlet-name>CountryListServlet</servlet-name>
<servlet-class>world.CountryListServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>CountryListServlet</servlet-name>
<url-pattern>/listc</url-pattern>
</servlet-mapping>
</web-app>
为web应用导入mysql-jdbc的jar包
把 mysql 的jar包放在WEB-INF/lib 目录下
放在WEB-INF/lib 下指的是能够web应用中找到对应的class，如果要在eclipse中做调试，还是需要为项目添加该jar才可以。
3增加
准备增加的页面addc.html
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
表示用UTF-8显示中文，同时浏览器也会使用UTF-8编码提交中文
form:
action设置为addHero路径
method设置为post 也是为了提交中文
在web目录下添加
<!DOCTYPE html>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<form action="addc" method="post">
国家名称 ： <input type="text" name="name"> <br>
国土面积： <input type="text" name="surfacearea"> <br>
人口数量： <input type="text" name="population"> <br>
<input type="submit" value="增加 ">
</form>
编写 CAddServlet
HeroAddServlet 中根据浏览器传过来的参数，创建一个Hero对象。 接着通过HeroDAO把该对象保存到数据库中。
最后使用客户端跳转到listHero查看所有的Hero，就能看到新加入的Hero对象了
request.setCharacterEncoding(“UTF-8”);
表示使用UTF-8的方式获取浏览器传过来的中文
package world;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import world.country;
import world.countrydao;
public class CAddServlet extends HttpServlet {
protected void service(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
request.setCharacterEncoding("UTF-8");
country country = new country();
country.setName(request.getParameter("name"));
country.setsurfacearea(Float.parseFloat(request.getParameter("surfacearea")));
country.setpopulation(Integer.parseInt(request.getParameter("population")));
new countrydao().add(country);
response.sendRedirect("/j2ee/listc");
}
}
配置web.xml
<servlet>
<servlet-name>HeroAddServlet</servlet-name>
<servlet-class>servlet.HeroAddServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>HeroAddServlet</servlet-name>
<url-pattern>/addHero</url-pattern>
</servlet-mapping>
测试
重启tomcat，访问增加页面http://127.0.0.1/addc.html
提交数据，接着客户端跳转到/j2ee/lisc，就可以显示新增加的这条数据了
4删除
修改CountryListServlet（提供delete超链）
修改CountryListServlet，多一个单元格，是一个超链
超链的href属性指向地址 /deleteC?id=242(每条不同的记录id不一样)
可以在左下角的浏览器状态栏里看到
package world;
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 world.country;
import world.countrydao;
public class CountryListServlet extends HttpServlet {
protected void service(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html; charset=UTF-8");
List<country> countries = new countrydao().list();
StringBuffer sb = new StringBuffer();
sb.append("<table align='center' border='1' cellspacing='0'>\r\n");
sb.append("<tr><td>id</td><td>name</td><td>surfacearea</td><td>population</td><td>delete</td></tr>\r\n");
String trFormat = "<tr><td>%d</td><td>%s</td><td>%f</td><td>%d</td><td><a href='deletec?id=%d'>delete</a></td></tr>\r\n";
for (country country : countries) {
String tr = String.format(trFormat, country.getId(), country.getName(), country.getsurfacearea(), country.getpopulation(), country.getId());
sb.append(tr);
}
sb.append("</table>");
response.getWriter().write(sb.toString());
}
}
编写CDeleteServlet
首先获取参数id
然后通过countrydao根据id，删除该对象
然后客户端跳转到 /listc
package world;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import world.country;
public class CDeleteServlet extends HttpServlet {
protected void service(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
int id = Integer.parseInt(request.getParameter("id"));
new countrydao().delete(id);
response.sendRedirect("/j2ee/listc");
}
}
配置web.xml
把/deletec指向CDeleteServlet
<servlet>
<servlet-name>CDeleteServlet</servlet-name>
<servlet-class>world.CDeleteServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>CDeleteServlet</servlet-name>
<url-pattern>/deletec</url-pattern>
</servlet-mapping>
5修改
修改CountryListServlet （提供edit超链）
新增加一列 edit，里面放上指向 /edit的超链
package world;
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 world.country;
import world.countrydao;
public class CountryListServlet extends HttpServlet {
protected void service(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html; charset=UTF-8");
List<country> countries = new countrydao().list();
StringBuffer sb = new StringBuffer();
sb.append("<table align='center' border='1' cellspacing='0'>\r\n");
sb.append("<tr><td>id</td><td>name</td><td>surfacearea</td><td>population</td><td>edit</td><td>delete</td></tr>\r\n");
String trFormat = "<tr><td>%d</td><td>%s</td><td>%f</td><td>%d</td><td><a href='edit?id=%d'>edit</a></td><td><a href='deletec?id=%d'>delete</a></td></tr>\r\n";
for (country country : countries) {
String tr = String.format(trFormat, country.getId(), country.getName(), country.getsurfacearea(), country.getpopulation(), country.getId(), country.getId());
sb.append(tr);
}
sb.append("</table>");
response.getWriter().write(sb.toString());
}
}
准备CEditServlet（获取历史数据）
CEditServlet 根据浏览器传过来的id获取一个country对象
然后根据这个对象，准备一个类似add.html的页面，不同之处在于每个输入框都是有值的。
最后还会提供一个type="hidden"的input,用于提交id到路径/update
package world;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import world.country;
import world.countrydao;
public class CEditServlet extends HttpServlet {
protected void service(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
int id = Integer.parseInt(request.getParameter("id"));
country country = new countrydao().get(id);
StringBuffer format = new StringBuffer();
response.setContentType("text/html; charset=UTF-8");
format.append("<!DOCTYPE html>");
format.append("<form action='update' method='post'>");
format.append("国家名称： <input type='text' name='name' value='%s' > <br>");
format.append("国土面积： <input type='text' name='surfacearea' value='%f' > <br>");
format.append("人口数量： <input type='text' name='population' value='%d' > <br>");
format.append("<input type='hidden' name='id' value='%d'>");
format.append("<input type='submit' value='更新'>");
format.append("</form>");
String html = String.format(format.toString(), country.getName(), country.getsurfacearea(), country.getpopulation(), country.getId());
response.getWriter().write(html);
}
}
准备CUpdateServlet（修改数据）
package world;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import world.country;
import world.countrydao;
public class CUpdateServlet extends HttpServlet {
protected void service(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
request.setCharacterEncoding("UTF-8");
country country = new country();
country.setId(Integer.parseInt(request.getParameter("id")));
country.setName(request.getParameter("name"));
country.setsurfacearea(Float.parseFloat(request.getParameter("surfacearea")));
country.setpopulation(Integer.parseInt(request.getParameter("population")));
new countrydao().update(country);
response.sendRedirect("/j2ee/listc");
}
}
配置web.xml
<servlet>
<servlet-name>CEditServlet</servlet-name>
<servlet-class>world.CEditServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>CEditServlet</servlet-name>
<url-pattern>/edit</url-pattern>
</servlet-mapping>
<servlet>
<servlet-name>CUpdateServlet</servlet-name>
<servlet-class>world.CUpdateServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>CUpdateServlet</servlet-name>
<url-pattern>/update</url-pattern>
</servlet-mapping>
三，总结
以上便是整个CURD案例的全部源代码了，每一步都有详细的介绍，虽然参考了其他的学习案例，但是本测试是根据mysql的案例类专门设计的。测试的过程中，基本把所有的报错都踩了一边，略有感慨，小写一篇文章以分享和记录。
