📄 query0mysql.java
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// servlet Query0 as first 3tier example
// mySQL version; change name + the first few lines of "lookup",
// and make sure the query does not end with a semi-colon.
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.sql.*;
public class Query0MySQL extends HttpServlet {
public void doGet (HttpServletRequest req,
HttpServletResponse res)
throws ServletException, IOException{
res.setContentType("text/html");
PrintWriter out=res.getWriter();
String theName=req.getParameter("theName");
String qResult=lookup(theName); // does all database work
// SELECT THENUMBER (in PHONEBOOK) where THENAME=theName
String title="Query Result: Phone Number for "+theName;
wrapInHTMLPage(out,qResult,title); // does all output HTML work
} // end of doGet()
public void doPost (HttpServletRequest req,
HttpServletResponse res)
throws ServletException, IOException{
doGet(req,res);
}
public void wrapInHTMLPage(PrintWriter out,String qResult,String title)
throws IOException {
out.println("<HTML><HEAD><TITLE> "+title+" </TITLE></HEAD>");
out.println("<BODY> <H1>"+title+"</H1>");
out.println(qResult);
out.println("</BODY></HTML>");
}
public String lookup(String key){
// variables for database work
String driverName="org.gjt.mm.mysql.Driver";
String dbURL="jdbc:mysql://localhost/PHONEBOOK/";
String theUser=""; String thePwd="";
String qString="SELECT THENUMBER FROM PHONEBOOK WHERE THENAME='"+key+"'";
try{
Class.forName(driverName);
Connection con=DriverManager.getConnection(dbURL,theUser,thePwd);
// selects value of THENUMBER from PHONEBOOK where THENAME is V;
Statement stmt=con.createStatement();
ResultSet res=stmt.executeQuery(qString);
String value;
if(null==res)value="db failure on "+key;
else if(res.next())value=res.getString(1);
else value="No such name as "+key; // empty result set
if(res!=null)res.close();
con.close();
return value;
}catch (java.lang.Exception ex)
{ex.printStackTrace(); return ""+ex;}
}
}
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