Database access help

Question

Hi All,
I am having major difficulties with my web application on Sun Web Server 6.1.
After a few days of moderate use (ca. 60 database accesses an hour), my web
server locks up and gives time out errors when requests are made.
After discussing this with fellow programmers, I thought my problem
stems from the database access I use. I wasn't using database connection
pooling, so I thought that might be the answer.
Using the Web server's JDBC Connection Pooling, I set up pooling to work with my application.
Everything seemed to work fine, but after a few days of use, the web server once again locked
up.
Below, please find the class I use to query databases. Do you have suggestions as to how to stream this class or suggestions as to where errors might lurk? Can you see any potential issues with the code I have written?
This class is accessed in the following way: From another class, this call is made:
ConnectAndQuery caq = new ConnectAndQuery();
Vector result = caq.getSelect("Select * from table", theDatabaseIwanttoAccess);
--> now goes to appropriate method in below ConnectAndQuery class
------------------------- ConnectAndQuery.class ----------------------------------------------------
import java.io.*;
import java.net.*;
import java.util.*;
import java.sql.*;
import javax.sql.*;
import javax.naming.InitialContext;
import com.sun.gscc.backend.PropertiesGrabber;
import com.sun.gscc.backend.Communicator;
* Manages database connections.
* @author me
* @version 1.0, 2003-12-02
public class ConnectAndQuery {
protected String sql = "";
protected String dbName = "";
public Connection conn;
public DataSource source;
public Statement stmt;
PropertiesGrabber pg = new PropertiesGrabber();
Communicator c = new Communicator();
* Setter for the sql variable.
* @param givenSql The sql required to process
public void setSql(java.lang.String givenSql) {
sql = givenSql;
* Sets the dbName needed to commect
* to the correct database.
* @param givenDbName Name of the database - name and connections specified within this class
public void setDbName(java.lang.String givenDbName) {
dbName = givenDbName;
* Check completeness of data.
* If sql or dbName not present it'll return false.
* @return String Checks if data is available
protected String checkDataAvailability(){
String returnValue = "";
if(dbName == ""){
returnValue += "\nNo database selected for query";
if(sql == ""){
returnValue += "\nNo SQL statement for query action";
return returnValue;
* Returns the appropriate connection to the required database.
* @return String connection string
* @exception SQLException
* @exception Exception
protected String getConnection(){
try{
InitialContext initContext = new InitialContext();
// First, if test conditions, switch to appropriate test databases.
if(dbName == "sccweb" && pg.getValue("testConditions") != null && pg.getValue("testConditions").equals("true")){
dbName = "yikes";
if(dbName == "maize" && pg.getValue("testConditions") != null && pg.getValue("testConditions").equals("true")){
dbName = "thefarm";
// Then, get connection from configured pool
source = (DataSource) initContext.lookup("java:comp/env/jdbc/" + dbName);
conn = source.getConnection();
stmt = conn.createStatement();
//System.err.println("Opening: " + conn.toString());
return conn.toString();
}catch (SQLException e){
c.emailThis(pg.getValue("adminEmail"), "SCCWebError", "SCCWeb Error: [ConnectAndQuery.getConnection] SQLException", "dbName tried: " + dbName + "\nSQLException: " + e.toString());
return "ConnectAndQuery, SQL Exception:\n" + e.toString();
}catch (Exception e){
c.emailThis(pg.getValue("adminEmail"), "SCCWebError", "SCCWeb Error: [ConnectAndQuery.getConnection] Exception", "dbName tried: " + dbName + "\nException: " + e.toString());
return "ConnectAndQuery, Some other getConnection Exception:\n" + e.toString();
* Takes care of insert, update and delete requests.
* Must have set both dbName as well as the sql String.
* Will return number of rows affected as String.
* @return String Number of rows affected
* @exception SQLException
* @exception Exception
public String getInsertDelete() {
// If insufficient data, bail out miserably
String complete = checkDataAvailability();
String returnValue = "not set";
if(complete != ""){
return "Complete Error: " + complete;
}else{
int rv = 0;
try{
String success = getConnection(); // get this from another function to get correct db
rv = stmt.executeUpdate(sql);
returnValue = "" + rv;
}catch (Exception e){
c.emailThis(pg.getValue("adminEmail"), "SCCWebError", "SCCWeb Error: [ConnectAndQuery.getInsertDelete] Exception", "getInsertDelete Exception: " + e.toString() + "\nWith: " + sql);
returnValue = "ConnectAndQuery, at getInsertDelete, Some other Exception:\n" + e.toString();
}finally{
try{
stmt.close();
conn.close();
}catch(Exception e){
c.emailThis(pg.getValue("adminEmail"), "SCCWebError", "SCCWeb Error: [ConnectAndQuery.getInsertDelete] Exception", "Close() Exception: " + e.toString());
return returnValue;
* Processes Insert and Delete requests with given SQL and DB Name.
* @param givenSql
* @param givenDbName
* @return String Number of rows affected
public String getInsertDelete(String givenSql, String givenDbName){
sql = givenSql;
dbName = givenDbName;
return getInsertDelete();
* Takes care of Select statements.
* Must have set both dbName as well as the sql String.
* Will return a vector.
* @return Vector of Hashes containing the Results of the query
* @exception SQLException
* @exception Exception
public Vector getSelect(){
// If insufficient data, bail out miserably
String complete = checkDataAvailability();
String returnTest = "not set";
Vector returnValue = new Vector();
String connectionString = "not set";
if(complete != ""){
returnTest = "Complete Error: " + complete;
}else{
try{
connectionString = getConnection();
StringBuffer query = new StringBuffer(sql);
ResultSet result = stmt.executeQuery(query.toString());
ResultSetMetaData rsmd = result.getMetaData();
while(result.next()){
Hashtable hash = new Hashtable();
for(int i = 1; i <= rsmd.getColumnCount(); i++){
//System.err.println("-------------------------------");
//System.err.println("SQL: " + sql);
//System.err.println("Index: " + i);
//System.err.println("Test: " + rsmd.getColumnName(i));
//System.err.println("Result: " + result.getString(i));
if(result.getString(i) != null){
hash.put(rsmd.getColumnName(i),result.getString(i));
}else{
hash.put(rsmd.getColumnName(i),"");
returnValue.addElement(hash);
}catch (Exception e){
c.emailThis(pg.getValue("adminEmail"), "SCCWebError", "SCCWeb Error: [ConnectAndQuery.getSelect] Exception", "getSelect Exception: " + e.toString() + "\nWith: " + sql);
returnTest = "ConnectAndQuery, getSelect, Some other getSelect Exception:\n" + e.toString();
}finally{
try{
stmt.close();
conn.close();
//System.err.println("closing: " + connectionString);
}catch(Exception e){
c.emailThis(pg.getValue("adminEmail"), "SCCWebError", "SCCWeb Error: [ConnectAndQuery.getSelect] Exception", "Close() Exception: " + e.toString());
return returnValue;
* Takes care of Select statements with given SQL.
* Must have set both dbName as well as the sql String.
* Will return a vector.
* @return Vector with Results of the query
* @exception SQLException
* @exception Exception
public Vector getSelect(String givenSql, String givenDbName){
sql = givenSql;
dbName = givenDbName;
return getSelect();
}

Answer 1

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