代码实现
开发工具：IDEA
不进行分离数据库连接
在web.xml中进行servlet配置
<servlet>
<servlet-name>DataServlet</servlet-name>
<servlet-class>com.jzk.firstservlet.DataServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>DataBase</servlet-name>
<url-pattern>/data.bin</url-pattern>
</servlet-mapping>
servlet的具体实现
所需要的包，下面写的时候IDEA会帮助自动导入
package com.jzk.firstservlet;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.*;
public class DataServlet extends HttpServlet {
@Override
public void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
Connection cn = null;
try {
Class.forName("com.mysql.jdbc.Driver"); //建立数据库驱动
try {
cn = DriverManager.getConnection("jdbc:mysql://localhost:3306/******","user","123456"); //建立数据库连接，三个参数对应了数据库的url、user、password，第一个****写的是数据库名称
} catch (SQLException e) {
e.printStackTrace();
}
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
PrintWriter out =resp.getWriter(); //新建输出流
Statement st = null;
String sql = "select numbers, namess, price from shopping"; //测试用的sql语句
try {
st = cn.createStatement(); //用于向已经建立的数据库发送sql语句
} catch (SQLException e) {
e.printStackTrace();
}
ResultSet rs = null;
try {
rs = st.executeQuery(sql); //建立结果集，返回执行sql语句之后结果
} catch (SQLException e) {
e.printStackTrace();
}
while(true){
//反复循环，直到rs搜索到最后一条数据
try {
if (rs.next()){
//访问数据库要干的事情
}else{
break;
};
} catch (SQLException e) {
e.printStackTrace();
}
}
}
}
分离数据库连接
思想：将建立连接的这部分独立出来做成一个servlet，配置在web.xml中
web.xml的配置
设立四个初始参数，分别对应驱动类名、url、user、password，最后load-on-startup参数是用于无mapping时候，servlet的自启动，否则这个servlet将不会启动
<servlet>
<servlet-name>DataBase</servlet-name>
<servlet-class>com.jzk.firstservlet.DataBase</servlet-class>
<init-param>
<param-name>driver</param-name>
<param-value>com.mysql.jdbc.Driver</param-value>
</init-param>
<init-param>
<param-name>url</param-name>
<param-value>jdbc:mysql://localhost:3306/test</param-value>
</init-param>
<init-param>
<param-name>user</param-name>
<param-value>root</param-value>
</init-param>
<init-param>
<param-name>pass</param-name>
<param-value>123456</param-value>
</init-param>
<load-on-startup>0</load-on-startup>
</servlet>
servlet的具体实现
DataBase类
package com.jzk.firstservlet;
import javax.servlet.http.HttpServlet;
import java.sql.Connection;
import java.sql.DriverManager;
public class DataBase extends HttpServlet {
private static String driver;
private static String url;
private static String user;
private static String pass;
public void init(){
//通过这个方法来获得配置在web.xml里的四个参数
driver = this.getInitParameter("driver");
url = this.getInitParameter("url");
user = this.getInitParameter("user");
pass = this.getInitParameter("pass");
}
public static Connection getConnection(){
//该方法用于建立数据库连接，返回Connection 对象
Connection cn= null;
try{
Class.forName(driver);
cn = DriverManager.getConnection(url,user,pass);
}catch (Exception e){
e.printStackTrace();
}
return cn;
}
}
Servlet类
package com.jzk.firstservlet;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.*;
public class DataServlet extends HttpServlet {
@Override
public void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
Connection cn = DataBase.getConnection(); //与不分离连接的区别在这里，所有的连接配置都在DataBase中，这里只需建立连接即可
PrintWriter out =resp.getWriter(); //新建输出流
Statement st = null;
String sql = "select numbers, namess, price from shopping"; //测试用的sql语句
try {
st = cn.createStatement(); //用于向已经建立的数据库发送sql语句
} catch (SQLException e) {
e.printStackTrace();
}
ResultSet rs = null;
try {
rs = st.executeQuery(sql); //建立结果集，返回执行sql语句之后结果
} catch (SQLException e) {
e.printStackTrace();
}
while(true){
//反复循环，直到rs搜索到最后一条数据
try {
if (rs.next()){
//访问数据库要干的事情
}else{
break;
};
} catch (SQLException e) {
e.printStackTrace();
}
}
}
}
遇到的问题
- IDEA需要手动导入数据库驱动的jar包，否则在IDEA调试的时候，会出现如下错误
java.lang.ClassNotFoundException: com.mysql.jdbc.Driver
解决方法1：
- 在WEB-INF下建立目录，并命名lib
- 将下载好的驱动jar包复制粘贴到该目录下，
- 右击，“add as Library”
解决方法2：
- file-Project Structure-Library，点击+号，选择java，找到下载好的jar包，OK。
- 可能会在Project Structure界面左侧最后一栏Problem出现提示错误，点击fix-add ‘mysql-connector-java-5.1.34’ to the artifacts.