How do loop through an XML file?

[Laurence Turpin]

Hello

I'm using GWT 2.4 on Windows 7
I'm trying to parse the following XML file:


<?xml version="1.0" encoding="UTF-8"?> <trainlog> <session date="2001-11-19" type="running" heartrate="158"> <duration>PT45M</duration> <distance units="miles">5.5</distance> <location>Warner Park</location> <comments>Mid-morning run, a little winded throughout.</comments> </session> <session date="2001-11-21" type="cycling" heartrate="153"> <duration>PT2H30M</duration> <distance units="miles">37.0</distance> <location>Natchez Trace Parkway</location> <comments>Hilly ride, felt strong as an ox.</comments> </session> <session date="2001-11-24" type="running" heartrate="156"> <duration>PT1H30M</duration> <distance units="miles">8.5</distance> <location>Warner Park</location> <comments>Afternoon run, felt reasonably strong</comments> </session> </trainlog>

The problem is there are 3 session nodes and I need have a loop in my program.
so it is:

While session
parse session
get next session

but I don't know how to do the loop.
I have tried to do it with a for loop but it doesn't work correctly.
I get the first session data 3 times.
When what I want is all of the 3 different session information.

Here is the program I have so far:

package net.talktalk.turpin.laurie.TrainingLogXML.client;

import com.google.gwt.core.client.EntryPoint;
import com.google.gwt.event.dom.client.ClickEvent;
import com.google.gwt.event.dom.client.ClickHandler;
import com.google.gwt.http.client.Request;
import com.google.gwt.http.client.RequestBuilder;
import com.google.gwt.http.client.RequestCallback;
import com.google.gwt.http.client.RequestException;
import com.google.gwt.http.client.Response;
import com.google.gwt.user.client.Window;
import com.google.gwt.user.client.rpc.AsyncCallback;
import com.google.gwt.user.client.ui.Button;
import com.google.gwt.user.client.ui.Grid;
import com.google.gwt.user.client.ui.RootPanel;
import com.google.gwt.xml.client.DOMException;
import com.google.gwt.xml.client.Document;
import com.google.gwt.xml.client.Element;
import com.google.gwt.xml.client.Node;
import com.google.gwt.xml.client.XMLParser;

public class TrainingLogXML implements EntryPoint {
  
  static final String xmlurl = "TrainingLog.xml";
  private String xmlText = null;
  Grid grid;
 
  public void onModuleLoad() {
    grid = new Grid(4, 9);
    grid.setText(1, 0, "Session 1");
    grid.setText(2, 0, "Session 2");
    grid.setText(3, 0, "Session 3");
    grid.setText(0, 1, "Date");
    grid.setText(0, 2, "Type");
    grid.setText(0, 3, "Heart Rate");
    grid.setText(0, 4, "Duration");
    grid.setText(0, 5, "Distance");
    grid.setText(0, 6, "Units");
    grid.setText(0, 7, "Location");
    grid.setText(0, 8, "Comment");
    httpGetFile(xmlurl, new AsyncCallback<String>() {
      public void onFailure(Throwable caught) {
        xmlText = "Error";
      }
      
      public void onSuccess(String xmlData) {
        xmlText = xmlData;
      }
    });
    Button button = new Button("Load Grid");
    button.addClickHandler(new ClickHandler() {
      public void onClick(ClickEvent event) {
        parseTrainingLog(xmlText);
        RootPanel.get("slot2").add(grid);
      }
    });
    RootPanel.get("slot1").add(button);
       
  }
  
  private void parseTrainingLog(String xmlText){
        
    try {
      // parse the XML document into a DOM
      Document trainingLogDom = XMLParser.parse(xmlText);
      
      // Loop throw each session
      for(int i = 0; i < 3; i++) {
        Node sessionNode = trainingLogDom.getElementsByTagName("session").item(0);
        String date = ((Element)sessionNode).getAttribute("date");
        String type = ((Element)sessionNode).getAttribute("type");
        String heartRate = ((Element)sessionNode).getAttribute("heartrate");
        
        String duration = trainingLogDom.getElementsByTagName("duration").item(0).getFirstChild().getNodeValue();
        
        Node distanceNode = trainingLogDom.getElementsByTagName("distance").item(0);
        String units =((Element)distanceNode).getAttribute("units");
        String distance = trainingLogDom.getElementsByTagName("distance").item(0).getFirstChild().getNodeValue();
        
        String location = trainingLogDom.getElementsByTagName("location").item(0).getFirstChild().getNodeValue();
        
        String comment = trainingLogDom.getElementsByTagName("comments").item(0).getFirstChild().getNodeValue();
        
        int j =1;
        grid.setText(i+1, j++, date);
        grid.setText(i+1, j++, type);
        grid.setText(i+1, j++, heartRate);
        grid.setText(i+1, j++, duration);
        grid.setText(i+1, j++, distance);
        grid.setText(i+1, j++, units);
        grid.setText(i+1, j++, location);
        grid.setText(i+1, j++, comment);
      }
        
    } catch (DOMException e) {
      Window.alert("Could not parse XML document.");
    }
  }
  
  public static void httpGetFile(final String url, final AsyncCallback<String> callback) {
    final RequestBuilder rb = new RequestBuilder(RequestBuilder.GET, url);
    rb.setCallback(new RequestCallback() {
      public void onResponseReceived(Request request, Response response) {
        try {
          final int responseCode = response.getStatusCode() / 100;
          if (url.startsWith("file:/") || (responseCode == 2)) {
            callback.onSuccess(response.getText());
          } else {
            callback.onFailure(new IllegalStateException("HttpError#" + response.getStatusCode() + " - " + response.getText()));
            }
        } catch (Throwable e) {
          callback.onFailure(e);
        }
      }
      public void onError(Request request, Throwable exception) {
        callback.onFailure(exception);
      }
    });
    try {
      rb.send();
    } catch (RequestException e) {
      callback.onFailure(e);
    }
  }
}

The for loop is where the problem is

[Paul Clapham]

At line 69 you get the first of the three <session> elements. You do that every time through the loop.

Why don't you just get all of the <session> elements and loop through them? (Hint: Hard-coding the number "3" is both unnecessary and wrong.)

[Laurence Turpin]

Thank you Paul Clapham for replying I now have a program that works.
I replaced line 69 with :

Node sessionNode = trainingLogDom.getElementsByTagName("session").item(i);

I replaced item(i) where ever item(0) occurred in my program.

It now works
However I still have one query.
Suppose that the number of sessions were 100s or more.
They would be too many to count.
What I really need to be able to do is parse all the session elements without know how many there are?

The basic structure of the loop needs to be:
----------------------------------------------------------------------------
While session elements to parse
{
parse session element
get next session element
}
----------------------------------------------------------------------------

Below is the revised program I now have

package net.talktalk.turpin.laurie.TrainingLogXML.client;

import com.google.gwt.core.client.EntryPoint;
import com.google.gwt.event.dom.client.ClickEvent;
import com.google.gwt.event.dom.client.ClickHandler;
import com.google.gwt.http.client.Request;
import com.google.gwt.http.client.RequestBuilder;
import com.google.gwt.http.client.RequestCallback;
import com.google.gwt.http.client.RequestException;
import com.google.gwt.http.client.Response;
import com.google.gwt.user.client.Window;
import com.google.gwt.user.client.rpc.AsyncCallback;
import com.google.gwt.user.client.ui.Button;
import com.google.gwt.user.client.ui.Grid;
import com.google.gwt.user.client.ui.RootPanel;
import com.google.gwt.xml.client.DOMException;
import com.google.gwt.xml.client.Document;
import com.google.gwt.xml.client.Element;
import com.google.gwt.xml.client.Node;
import com.google.gwt.xml.client.XMLParser;

public class TrainingLogXML implements EntryPoint {
  
  static final String xmlurl = "TrainingLog.xml";
  private String xmlText = null;
  Grid grid;
 
  public void onModuleLoad() {
    grid = new Grid(4, 9);
    grid.setText(1, 0, "Session 1");
    grid.setText(2, 0, "Session 2");
    grid.setText(3, 0, "Session 3");
    grid.setText(0, 1, "Date");
    grid.setText(0, 2, "Type");
    grid.setText(0, 3, "Heart Rate");
    grid.setText(0, 4, "Duration");
    grid.setText(0, 5, "Distance");
    grid.setText(0, 6, "Units");
    grid.setText(0, 7, "Location");
    grid.setText(0, 8, "Comment");
    grid.addStyleName("gridStyle");
    httpGetFile(xmlurl, new AsyncCallback<String>() {
      public void onFailure(Throwable caught) {
        xmlText = "Error";
      }
      
      public void onSuccess(String xmlData) {
        xmlText = xmlData;
      }
    });
    Button button = new Button("Load Grid");
    button.addClickHandler(new ClickHandler() {
      public void onClick(ClickEvent event) {
        parseTrainingLog(xmlText);
        RootPanel.get("slot2").add(grid);
      }
    });
    RootPanel.get("slot1").add(button);
       
  }
  
  private void parseTrainingLog(String xmlText){
        
    try {
      // parse the XML document into a DOM
      Document trainingLogDom = XMLParser.parse(xmlText);
      
      // Loop throw each session
      for(int i = 0; i < 3; i++) {
        Node sessionNode = trainingLogDom.getElementsByTagName("session").item(i);
        String date = ((Element)sessionNode).getAttribute("date");
        String type = ((Element)sessionNode).getAttribute("type");
        String heartRate = ((Element)sessionNode).getAttribute("heartrate");
        
        String duration = trainingLogDom.getElementsByTagName("duration").item(i).getFirstChild().getNodeValue();
        
        Node distanceNode = trainingLogDom.getElementsByTagName("distance").item(i);
        String units =((Element)distanceNode).getAttribute("units");
        String distance = trainingLogDom.getElementsByTagName("distance").item(i).getFirstChild().getNodeValue();
        
        String location = trainingLogDom.getElementsByTagName("location").item(i).getFirstChild().getNodeValue();
        
        String comment = trainingLogDom.getElementsByTagName("comments").item(i).getFirstChild().getNodeValue();
        
        int j =1;
        grid.setText(i+1, j++, date);
        grid.setText(i+1, j++, type);
        grid.setText(i+1, j++, heartRate);
        grid.setText(i+1, j++, duration);
        grid.setText(i+1, j++, distance);
        grid.setText(i+1, j++, units);
        grid.setText(i+1, j++, location);
        grid.setText(i+1, j++, comment);
      }
        
    } catch (DOMException e) {
      Window.alert("Could not parse XML document.");
    }
  }
  
  public static void httpGetFile(final String url, final AsyncCallback<String> callback) {
    final RequestBuilder rb = new RequestBuilder(RequestBuilder.GET, url);
    rb.setCallback(new RequestCallback() {
      public void onResponseReceived(Request request, Response response) {
        try {
          final int responseCode = response.getStatusCode() / 100;
          if (url.startsWith("file:/") || (responseCode == 2)) {
            callback.onSuccess(response.getText());
          } else {
            callback.onFailure(new IllegalStateException("HttpError#" + response.getStatusCode() + " - " + response.getText()));
            }
        } catch (Throwable e) {
          callback.onFailure(e);
        }
      }
      public void onError(Request request, Throwable exception) {
        callback.onFailure(exception);
      }
    });
    try {
      rb.send();
    } catch (RequestException e) {
      callback.onFailure(e);
    }
  }
}

[Laurence Turpin]

Finally managed to work out how to do the while loop.
Here is the solution shown below.

package net.talktalk.turpin.laurie.TrainingLogXML.client;

import com.google.gwt.core.client.EntryPoint;
import com.google.gwt.event.dom.client.ClickEvent;
import com.google.gwt.event.dom.client.ClickHandler;
import com.google.gwt.http.client.Request;
import com.google.gwt.http.client.RequestBuilder;
import com.google.gwt.http.client.RequestCallback;
import com.google.gwt.http.client.RequestException;
import com.google.gwt.http.client.Response;
import com.google.gwt.user.client.Window;
import com.google.gwt.user.client.rpc.AsyncCallback;
import com.google.gwt.user.client.ui.Button;
import com.google.gwt.user.client.ui.Grid;
import com.google.gwt.user.client.ui.RootPanel;
import com.google.gwt.xml.client.DOMException;
import com.google.gwt.xml.client.Document;
import com.google.gwt.xml.client.Element;
import com.google.gwt.xml.client.Node;
import com.google.gwt.xml.client.XMLParser;

public class TrainingLogXML implements EntryPoint {
  
  static final String xmlurl = "TrainingLog.xml";
  private String xmlText = null;
  Grid grid;
 
  public void onModuleLoad() {
    grid = new Grid(4, 9);
    grid.setText(1, 0, "Session 1");
    grid.setText(2, 0, "Session 2");
    grid.setText(3, 0, "Session 3");
    grid.setText(0, 1, "Date");
    grid.setText(0, 2, "Type");
    grid.setText(0, 3, "Heart Rate");
    grid.setText(0, 4, "Duration");
    grid.setText(0, 5, "Distance");
    grid.setText(0, 6, "Units");
    grid.setText(0, 7, "Location");
    grid.setText(0, 8, "Comment");
    grid.addStyleName("gridStyle");
    httpGetFile(xmlurl, new AsyncCallback<String>() {
      public void onFailure(Throwable caught) {
        xmlText = "Error";
      }
      
      public void onSuccess(String xmlData) {
        xmlText = xmlData;
      }
    });
    Button button = new Button("Load Grid");
    button.addClickHandler(new ClickHandler() {
      public void onClick(ClickEvent event) {
        parseTrainingLog(xmlText);
        RootPanel.get("slot2").add(grid);
      }
    });
    RootPanel.get("slot1").add(button);
       
  }
  
  private void parseTrainingLog(String xmlText){
        
    try {
      // parse the XML document into a DOM
      Document trainingLogDom = XMLParser.parse(xmlText);
      
      // Loop throw each session
        int i = 0;
        while (trainingLogDom.getElementsByTagName("session").item(i) != null) {
        Node sessionNode = trainingLogDom.getElementsByTagName("session").item(i);
        String date = ((Element)sessionNode).getAttribute("date");
        String type = ((Element)sessionNode).getAttribute("type");
        String heartRate = ((Element)sessionNode).getAttribute("heartrate");
        
        String duration = trainingLogDom.getElementsByTagName("duration").item(i).getFirstChild().getNodeValue();
        
        Node distanceNode = trainingLogDom.getElementsByTagName("distance").item(i);
        String units =((Element)distanceNode).getAttribute("units");
        String distance = trainingLogDom.getElementsByTagName("distance").item(i).getFirstChild().getNodeValue();
        
        String location = trainingLogDom.getElementsByTagName("location").item(i).getFirstChild().getNodeValue();
        
        String comment = trainingLogDom.getElementsByTagName("comments").item(i).getFirstChild().getNodeValue();
        
        int j =1;
        grid.setText(i+1, j++, date);
        grid.setText(i+1, j++, type);
        grid.setText(i+1, j++, heartRate);
        grid.setText(i+1, j++, duration);
        grid.setText(i+1, j++, distance);
        grid.setText(i+1, j++, units);
        grid.setText(i+1, j++, location);
        grid.setText(i+1, j++, comment);
        i++;
      }
        
    } catch (DOMException e) {
      Window.alert("Could not parse XML document.");
    }
  }
  
  public static void httpGetFile(final String url, final AsyncCallback<String> callback) {
    final RequestBuilder rb = new RequestBuilder(RequestBuilder.GET, url);
    rb.setCallback(new RequestCallback() {
      public void onResponseReceived(Request request, Response response) {
        try {
          final int responseCode = response.getStatusCode() / 100;
          if (url.startsWith("file:/") || (responseCode == 2)) {
            callback.onSuccess(response.getText());
          } else {
            callback.onFailure(new IllegalStateException("HttpError#" + response.getStatusCode() + " - " + response.getText()));
            }
        } catch (Throwable e) {
          callback.onFailure(e);
        }
      }
      public void onError(Request request, Throwable exception) {
        callback.onFailure(exception);
      }
    });
    try {
      rb.send();
    } catch (RequestException e) {
      callback.onFailure(e);
    }
  }
}