May 15, 2021 Servlet
This tutorial assumes that you already know how JDBC applications work. Before you start learning about servlet database access, make sure that you already have the appropriate JDBC environment settings and databases.
Starting with the basic concept, let's create a simple table and create a few records in the table.
To create an Employees table in the test database TEST, follow these steps:
Open the Command Line Prompt and change to the installation directory as follows:
C:\> C:\>cd Program Files\MySQL\bin C:\Program Files\MySQL\bin>
Sign in to the database as follows:
C:\Program Files\MySQL\bin>mysql -u root -p Enter password: ******** mysql>
Create an Employee table in the test database TEST, as follows:
mysql> use TEST;
mysql> create table Employees
(
id int not null,
age int not null,
first varchar (255),
last varchar (255)
);
Query OK, 0 rows affected (0.08 sec)
mysql>
Finally, create a few records in the Employee table, as follows:
mysql> INSERT INTO Employees VALUES (100, 18, 'Zara', 'Ali');
Query OK, 1 row affected (0.05 sec)
mysql> INSERT INTO Employees VALUES (101, 25, 'Mahnaz', 'Fatma');
Query OK, 1 row affected (0.00 sec)
mysql> INSERT INTO Employees VALUES (102, 30, 'Zaid', 'Khan');
Query OK, 1 row affected (0.00 sec)
mysql> INSERT INTO Employees VALUES (103, 28, 'Sumit', 'Mittal');
Query OK, 1 row affected (0.00 sec)
mysql>
The following example demonstrates how to use servlets to access the TEST database.
// 加载必需的库
import java.io.*;
import java.util.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.sql.*;
public class DatabaseAccess extends HttpServlet{
public void doGet(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException
{
// JDBC 驱动器名称和数据库的 URL
static final String JDBC_DRIVER="com.mysql.jdbc.Driver";
static final String DB_URL="jdbc:mysql://localhost/TEST";
// 数据库的用户名与密码，需要根据自己的设置
static final String USER = "root";
static final String PASS = "password";
// 设置响应内容类型
response.setContentType("text/html");
PrintWriter out = response.getWriter();
String title = "数据库结果";
String docType =
"<!doctype html public \"-//w3c//dtd html 4.0 " + "transitional//en\">\n";
out.println(docType +
"<html>\n" +
"<head><title>" + title + "</title></head>\n" +
"<body bgcolor=\"#f0f0f0\">\n" +
"<h1 align=\"center\">" + title + "</h1>\n");
try{
// 注册 JDBC 驱动器
Class.forName("com.mysql.jdbc.Driver");
// 打开一个连接
Connection conn = DriverManager.getConnection(DB_URL,USER,PASS);
// 执行 SQL 查询
Statement stmt = conn.createStatement();
String sql;
sql = "SELECT id, first, last, age FROM Employees";
ResultSet rs = stmt.executeQuery(sql);
// 展开结果集数据库
while(rs.next()){
// 通过字段检索
int id = rs.getInt("id");
int age = rs.getInt("age");
String first = rs.getString("first");
String last = rs.getString("last");
// 输出数据
out.println("ID: " + id + "<br>");
out.println(", Age: " + age + "<br>");
out.println(", First: " + first + "<br>");
out.println(", Last: " + last + "<br>");
}
out.println("</body></html>");
// 完成后关闭
rs.close();
stmt.close();
conn.close();
}catch(SQLException se){
// 处理 JDBC 错误
se.printStackTrace();
}catch(Exception e){
// 处理 Class.forName 错误
e.printStackTrace();
}finally{
// 最后是用于关闭资源的块
try{
if(stmt!=null)
stmt.close();
}catch(SQLException se2){
}
try{
if(conn!=null)
conn.close();
}catch(SQLException se){
se.printStackTrace();
}
}
}
}
Now let's compile the servlet above and create the following entry .xml the web server file:
....
<servlet>
<servlet-name>DatabaseAccess</servlet-name>
<servlet-class>DatabaseAccess</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>DatabaseAccess</servlet-name>
<url-pattern>/DatabaseAccess</url-pattern>
</servlet-mapping>
....
Now call this servlet and enter the link: The http://localhost:8080/DatabaseAccess will show the following response results:
数据库结果 ID: 100, Age: 18, First: Zara, Last: Ali ID: 101, Age: 25, First: Mahnaz, Last: Fatma ID: 102, Age: 30, First: Zaid, Last: Khan ID: 103, Age: 28, First: Sumit, Last: Mittal