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數(shù)據(jù)庫訪問
2018-08-12 21:20 更新
數(shù)據(jù)庫訪問
本教程假定你已經(jīng)了解了 JDBC 應(yīng)用程序的工作方式。在你開始學(xué)習(xí) servlet 數(shù)據(jù)庫訪問之前，確保你已經(jīng)有適當(dāng)?shù)?JDBC 環(huán)境設(shè)置和數(shù)據(jù)庫。
關(guān)于如何使用 JDBC 訪問數(shù)據(jù)庫及其環(huán)境配置的更多細(xì)節(jié)，你可以查看我們的 JDBC 教程。
從基本概念開始，讓我們創(chuàng)建一個簡單的表，并在表中創(chuàng)建幾條記錄，如下所示：
創(chuàng)建表
在 TEST 數(shù)據(jù)庫中創(chuàng)建 Employees 表，請按以下步驟進(jìn)行：
步驟 1
打開 Command Prompt，并改為安裝目錄，如下所示：
C:\>
C:\>cd Program Files\MySQL\bin
C:\Program Files\MySQL\bin>步驟 2
登錄數(shù)據(jù)庫，如下所示：
C:\Program Files\MySQL\bin>mysql -u root -p
Enter password: ********
mysql>步驟 3
在 TEST 數(shù)據(jù)庫中創(chuàng)建 Employee 表，如下所示：
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>創(chuàng)建數(shù)據(jù)記錄
最后在 Employee 表中創(chuàng)建幾條記錄，如下所示：
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>訪問數(shù)據(jù)庫
這里的例子演示了如何使用 Servlet 訪問 TEST 數(shù)據(jù)庫。
// Loading required libraries
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 driver name and database URL
static final String JDBC_DRIVER="com.mysql.jdbc.Driver";
static final String DB_URL="jdbc:mysql://localhost/TEST";
// Database credentials
static final String USER = "root";
static final String PASS = "password";
// Set response content type
response.setContentType("text/html");
PrintWriter out = response.getWriter();
String title = "Database Result";
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{
// Register JDBC driver
Class.forName("com.mysql.jdbc.Driver");
// Open a connection
conn = DriverManager.getConnection(DB_URL,USER,PASS);
// Execute SQL query
stmt = conn.createStatement();
String sql;
sql = "SELECT id, first, last, age FROM Employees";
ResultSet rs = stmt.executeQuery(sql);
// Extract data from result set
while(rs.next()){
//Retrieve by column name
int id = rs.getInt("id");
int age = rs.getInt("age");
String first = rs.getString("first");
String last = rs.getString("last");
//Display values
out.println("ID: " + id + "<br>");
out.println(", Age: " + age + "<br>");
out.println(", First: " + first + "<br>");
out.println(", Last: " + last + "<br>");
}
out.println("</body></html>");
// Clean-up environment
rs.close();
stmt.close();
conn.close();
}catch(SQLException se){
//Handle errors for JDBC
se.printStackTrace();
}catch(Exception e){
//Handle errors for Class.forName
e.printStackTrace();
}finally{
//finally block used to close resources
try{
if(stmt!=null)
stmt.close();
}catch(SQLException se2){
}// nothing we can do
try{
if(conn!=null)
conn.close();
}catch(SQLException se){
se.printStackTrace();
}//end finally try
} //end try
}
} 現(xiàn)在讓我們來編譯述 servlet 并在 web.xml 文件中創(chuàng)建以下條目：
....
<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>
....現(xiàn)在使用 URL http://localhost:8080/DatabaseAccess 調(diào)用這個 servlet，將顯示如下所示響應(yīng)：
Database Result
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
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