本文實例講述了Java實現JSP使用Servelt連接Oracle數據庫的方法。為了實現在Servlet 中連接數據庫，必須編寫Servlet 的類程序。將Servlet 類程序放到WEB 服務器的servlets 或者classes 目錄下面，為調用Servlet，需要創建發送Servlet 請求的HTML 文檔。本例通過(Driver)Class.forName(driverName).newInstance()方法來實現加載驅動程序，建立與數據庫連接。
具體程序代碼為：
1．Database 類繼承了HttpServlet 類，共有兩個方法：doGet()和displayResult()，代碼如下：
public class Database extends HttpServlet
{
public void doGet()；
public void displayResult(ResultSet results,PrintWriter out);
}
2．在doGet()方法中建立與數據庫的連接並執行查詢：
public void doGet()
{
HttpServletRequest request,
HttpServletResponse response
}
throws ServletException, IOException
{
PrintWriter out;
String title = "Simple Servlet connecting to Oracle DB";
response.setContentType("text/html;charset=GB2312");
out = response.getWriter();
out.println("<HTML><HEAD><TITLE>");
out.println(title);
out.println("</TITLE></HEAD><BODY>");
out.println("<H1>" + title + "</H1>");
out.println("<P>This is output from SimpleServlet.");
String driverName = "oracle.jdbc.driver.OracleDriver";
Driver d;
Connection con;
Statement stmt;
ResultSet results;
try
{
d = (Driver)Class.forName(driverName).newInstance();
con = DiverManager.getConnection("jdbc:oracle:thin:ndb/ndb@192.168.1.6:1521:PC6");
stmt = con.createStatement();
String sqlstr = "select * from data";
results = stmt.executeQuery(sqlstr);
displayResult(results,out);
stmt.close();
con.close();
}
catch (Exception e)
{
out.println("error: " + e.toString());
}
out.println("</BODY></HTML>");
out.close();
}
3．DisplayResult()方法顯示查詢結果:
public void displayResult(ResultSet results,PrintWriter out)
{
StringBuffer buf = new StringBuffer();
String temp;
try
{
ResultSetMetaData rsmd = results.getMetaData();
int numCols = rsmd.getColumnCount();
int i, rowcount = 0;
for (i=1; i <= numCols; i++)
{
if (i > 1) buf.append(",");
buf.append(rsmd.getColumnLabel(i));
}
buf.append("");
while (results.next() && rowcount < 100)
{
for (i=1; i <= numCols; i++)
{
if (i > 1) buf.append(",");
buf.append((results.getString(i)));
}
buf.append("<br>");
rowcount++;
}
out.println("<br>");
out.println(buf.toString());
results.close();
}
catch (Exception e)
{
out.println("error: " + e.toString());
return;
}
}
4．因為程序使用了JDBC 類、servlet 類和使用控制台輸出，所以需要引入如下的包：
import java.sql.*; import java.io.*; import javax.servlet.*; import javax.servlet.http.*;
5．編譯Database.java，產生Database.class 文件，將Database.class 放到WEB 服務器的servlets 目錄下，本例采用Java Web Server 作為WEB 服務器。配置好WEB 服務器，添加database.class，指定名稱為database。
6．編寫調用Servlet 的database.html 文件。代碼如下：
<html> <head> <title>Jsp使用Servlet連接數據庫</title> </head> <body> <center> <form action="/servlet/database" method="get"> <input name="action" type="submit" value="連接數據庫"> </form> </center> </body> </html>
