Who can help solve this XML/Servlet mystery?

Question

Hi,
I'm developing a servlet that accepts an HTTP request, contacts a database, processes the request and return an XML document back to the browser. The XML document returned is dependent on which selection a user makes.
The problem is that on first request, say user selects "choice one", the correct XML document is returned. However, when the browser's back button is used to go back and make the same choice as previous(ie "choice one"), Explorer 4.5 displays an empty page while netscape 4.5 return a document contains no data error.
I used oracle xmlclassgenerator to generate the classes that create the XML document to be returned. The problem certainly lies in the method of my servlet that uses these classes to generate the XML document because when I replace the whole method with println statement every thing works fine(but of course without the XML document).
The content of the method is as follows.
ACCOUNT acc = new ACCOUNT(id);
//Create a child and add child to root node
NUM_OF_RESIDENTS nr = new NUM_OF_RESIDENTS(num);
acc.addNode(nr);
//Create another child and add to root node
FIXED_COST fc = new FIXED_COST();
ELECTRICITY el = new ELECTRICITY(elec);
GAS g = new GAS(gas);
WASH_MACHINE wm = new WASH_MACHINE(wash);
WATER wat = new WATER(water);
OTHER oth = new OTHER(other);
fc.addNode(el);
fc.addNode(g);
fc.addNode(wm);
fc.addNode(wat);
fc.addNode(oth);
//finally add to root node
acc.addNode(fc);
//Create another child
TELEPHONE tl = new TELEPHONE();
SUBSCRIPTION sub = new SUBSCRIPTION(tel);
COST_PER_TICK cpt = new COST_PER_TICK(tick);
tl.addNode(sub);
tl.addNode(cpt);
acc.addNode(tl);
//Create another child
// PREVIOUS_ACCOUNT pacc = new PREVIOUS_ACCOUNT();
for(int i=0; i<previous_details.size(); i++){
//Create another child
PREVIOUS_ACCOUNT pacc = new PREVIOUS_ACCOUNT();
PreviousDetails pd = (PreviousDetails)previous_details.elementAt(i);
String name = pd.getName();
String credit = pd.getCredit();
String debit = pd.getDebit();
NAME n = new NAME(name);
LAST_CREDIT lc = new LAST_CREDIT(credit);
LAST_DEBIT ld = new LAST_DEBIT(debit);
pacc.addNode(n);
pacc.addNode(lc);
pacc.addNode(ld);
acc.addNode(pacc);
for(int i=0; i<acc_dates.size(); i++){
String str = (String)acc_dates.elementAt(i);
ACCOUNT_DATE ad = new ACCOUNT_DATE(str);
acc.addNode(ad);
acc.validateContent();
ByteArrayOutputStream out1 = new ByteArrayOutputStream(1024);
acc.print(out1);
res.setContentType("text/plain");
ServletOutputStream os = res.getOutputStream();
PrintWriter out = new PrintWriter(os);
out.println(out1.toString());
out.close();
catch(Exception e){}
Am I doing somthing wrong here?
Thanks.
null

Answer 1

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Steven Muench ([email protected]):
If you paste your code that's in the servlet into a file with a static main() method, and if you wrap the code with a for loop in Java that makes it execute 3 times in a row, does it work properly each of the the 3 times in this scenario?<HR></BLOCKQUOTE>
I have done as you requested. For your convenience I have pasted both the code and its output below.
import oracle.xml.classgen.*;
import oracle.xml.parser.*;
import java.io.*;
import java.util.*;
import java.sql.*;
import java.math.*;
public class CreateTest{
static String id = "10212";
public static void main (String args[]){
for(int i=0; i<3; i++){
System.out.println("Request started!");
testLoop();
static void testLoop(){
try{
System.out.println("Start DB contact");
DriverManager.registerDriver(new oracle.jdbc.driver.OracleDriver());
Connection conn =
DriverManager.getConnection ("jdbc:oracle:thin:@my_ip:sid","username", "passwd");
ResultSet rset;
Vector acc_dates = new Vector();
Vector previous_details = new Vector();
String elec = null;
String gas = null;
String wash = null;
String water = null;
String other = null;
String tel = null;
String tick = null;
String num = null;
Statement stmt = conn.createStatement();
rset = stmt.executeQuery("select NUM_OF_RESIDENTS from MEMBER WHERE ID="+id);
while(rset.next()){
num = String.valueOf(rset.getInt(1));
rset = stmt.executeQuery("select ELECTRICITY,GAS,WASH_MACHINE,WATER,OTHER from FIXED_COST where ID="+id);
while(rset.next()){
elec = String.valueOf(rset.getFloat(1));
gas = String.valueOf(rset.getFloat(2));
wash = String.valueOf(rset.getFloat(3));
water = String.valueOf(rset.getFloat(4));
other = String.valueOf(rset.getFloat(5));
rset = stmt.executeQuery("select SUBSCRIPTION,COST_PER_TICK from TELEPHONE WHERE id="+id);
while(rset.next()){
tel = String.valueOf(rset.getFloat(1));
tick = String.valueOf(rset.getFloat(2));
rset = stmt.executeQuery("select NICK_NAME, CREDIT, DEBIT from PREVIOUS_ACCOUNT WHERE LAST_ACCOUNT='yes' AND id="+id);
while(rset.next()){
String name = rset.getString(1);
String credit = String.valueOf(rset.getFloat(2));
String debit = String.valueOf(rset.getFloat(3));
PreviousDetails pd = new PreviousDetails(name,credit,debit);
previous_details.addElement(pd);
rset = stmt.executeQuery("select ACCOUNT_DATE from ACCOUNT_RESULT WHERE ID="+id);
while(rset.next()){
acc_dates.addElement(rset.getString(1));
rset.close();
stmt.close();
conn.close();
System.out.println("End DB contact");
generateXMLDocument(num,elec,gas,wash,water,other,tel,tick,previous_details,acc_dates);
catch(Exception e){e.printStackTrace();}
public static void generateXMLDocument(String num, String elec, String gas, String wash, String water, String other, String tel, String tick, Vector previous_details, Vector acc_dates){
try{
//Create the document root node
ACCOUNT acc = new ACCOUNT(id);
//Create a child and add child to root node
NUM_OF_RESIDENTS nr = new NUM_OF_RESIDENTS(num);
acc.addNode(nr);
//Create another child and add to root node
FIXED_COST fc = new FIXED_COST();
ELECTRICITY el = new ELECTRICITY(elec);
GAS g = new GAS(gas);
WASH_MACHINE wm = new WASH_MACHINE(wash);
WATER wat = new WATER(water);
OTHER oth = new OTHER(other);
fc.addNode(el);
fc.addNode(g);
fc.addNode(wm);
fc.addNode(wat);
fc.addNode(oth);
//finally add to root node
acc.addNode(fc);
//Create another child
TELEPHONE tl = new TELEPHONE();
SUBSCRIPTION sub = new SUBSCRIPTION(tel);
COST_PER_TICK cpt = new COST_PER_TICK(tick);
tl.addNode(sub);
tl.addNode(cpt);
acc.addNode(tl);
//Create another child
// PREVIOUS_ACCOUNT pacc = new PREVIOUS_ACCOUNT();
for(int i=0; i<previous_details.size(); i++){
//Create another child
PREVIOUS_ACCOUNT pacc = new PREVIOUS_ACCOUNT();
PreviousDetails pd = (Previou sDetails)previous_details.elementAt(i);
String name = pd.getName();
String credit = pd.getCredit();
String debit = pd.getDebit();
NAME n = new NAME(name);
LAST_CREDIT lc = new LAST_CREDIT(credit);
LAST_DEBIT ld = new LAST_DEBIT(debit);
pacc.addNode(n);
pacc.addNode(lc);
pacc.addNode(ld);
acc.addNode(pacc);
for(int i=0; i<acc_dates.size(); i++){
String str = (String)acc_dates.elementAt(i);
ACCOUNT_DATE ad = new ACCOUNT_DATE(str);
acc.addNode(ad);
acc.validateContent();
ByteArrayOutputStream out1 = new ByteArrayOutputStream(1024);
acc.print(out1);
System.out.println("The result is:");
System.out.println(out1.toString());
catch(Exception e){}
The output is:
Request started!
Start DB contact
End DB contact
The result is:
<!DOCTYPE ACCOUNT SYSTEM "file:/home/httpd/html/tydex/dtd/ACCOUNT_dtd.txt">
<ACCOUNT ID="10212">
<NUM_OF_RESIDENTS>3</NUM_OF_RESIDENTS>
<FIXED_COST>
<ELECTRICITY>0.0</ELECTRICITY>
<GAS>0.0</GAS>
<WASH_MACHINE>0.0</WASH_MACHINE>
<WATER>0.0</WATER>
<OTHER>0.0</OTHER>
</FIXED_COST>
<TELEPHONE>
<SUBSCRIPTION>0.0</SUBSCRIPTION>
<COST_PER_TICK>0.0</COST_PER_TICK>
</TELEPHONE>
<PREVIOUS_ACCOUNT>
<NAME>dsffd</NAME>
<LAST_CREDIT>0.0</LAST_CREDIT>
<LAST_DEBIT>0.0</LAST_DEBIT>
</PREVIOUS_ACCOUNT>
<PREVIOUS_ACCOUNT>
<NAME>dsfd</NAME>
<LAST_CREDIT>0.0</LAST_CREDIT>
<LAST_DEBIT>0.0</LAST_DEBIT>
</PREVIOUS_ACCOUNT>
<PREVIOUS_ACCOUNT>
<NAME>dsfdfs</NAME>
<LAST_CREDIT>0.0</LAST_CREDIT>
<LAST_DEBIT>0.0</LAST_DEBIT>
</PREVIOUS_ACCOUNT>
</ACCOUNT>
Request started!
Start DB contact
End DB contact
Request started!
Start DB contact
End DB contact
Thanks.
null