Dynamic image content in Java NetBeans Swing GUI

Question

I am an undergrad student working on creating a Java weather app (Executable JAR) with NetBeans IDE 7.4 and Swing GUI.So far I have managed to create this much. I have a very limited knowledge of Java as of now. I am having problems with loading images after the first time (that is problem loading the 2nd and further subsequent images onto another jFrame that is opened after clicking a jButton in jFrame 1) onto the GUI Panel. I have tried several methods including getResource() , ImageIcon and also tried Java 2-D documentation examples.

I had a partially success with ImageIcon, but after I have loaded one image I cannot load any others. The subsequent image(s) displayed is the same as before with no change and when I diagnosed with getImageLoadStatus() it returns a value of '8' which might indicate some connection problems. I need to load the images from a URL . Specifically I'm using Yahoo weather RSS feeds to implement everything in my program, including the images.

What is utterly baffling to me is that the same code works differently (in this case it doesn't work) when used in the same context. Please check below two snippets of code for further clarification

P.S. I don't know JSON/ XML parsing to get data , so what I've used is a very naive URL to string method.

Working Code in 1st jFrame >

 // TO GET CODE
        num = weather.indexOf("code");
        num1 = weather.indexOf(" ", num);
        String cod = weather.substring(num + 6, num1 - 1);

        String imgurl = "http://l.yimg.com/a/i/us/we/52/" + cod;
        String imgurl1 = imgurl + ".gif";
        System.out.println(imgurl1);

 // TO DISPLAY IMAGE 
        try{
         BufferedImage img = ImageIO.read(new URL(imgurl1));

      jLabel19.setIcon(new ImageIcon(img)); 
        }
        catch(Exception e){

        }

-- Non - Working Code in 2nd jFrame that opens up on clicking a button in jFrame 1 (

   // TO GET CODE
    num = weather_1.indexOf("day");
    num1 = weather_1.indexOf("code", num);
    num2 = weather_1.indexOf("/", num1);
    String cod = weather_1.substring(num1 + 6, num2 - 2);

    String imgurl = "http://l.yimg.com/a/i/us/we/52/" + cod;
    String imgurl1 = imgurl + ".gif";

        //TO GET IMAGE
     try{
     BufferedImage img = ImageIO.read(new URL(imgurl1));
   System.out.println(imgurl1);

    jLabel16.setIcon(new ImageIcon(img)); 
    }
    catch(Exception e){

    }

What is utterly baffling to me, is that if I change the variable 'imgurl1' to its URL form which is 'http://l.yimg.com/a/i/us/we/52/30.gif', then it works fine. But the code with the variable inside the "(new URL(imgurl1));" code worked the 1st time in jFrame 1.

Answer 1

So, I took at look at http://weather.yahooapis.com/forecastrss?w=1103816&u=c to see what it returns and got the following output...

<?xml version="1.0" encoding="UTF-8"?><rss xmlns:geo="http://www.w3.org/2003/01/geo/wgs84_pos#" xmlns:yweather="http://xml.weather.yahoo.com/ns/rss/1.0" version="2.0">
    <channel>

        <title>Yahoo! Weather - Melbourne, AU</title>
        <link>http://us.rd.yahoo.com/dailynews/rss/weather/Melbourne__AU/*http://weather.yahoo.com/forecast/ASXX0075_c.html</link>
        <description>Yahoo! Weather for Melbourne, AU</description>
        <language>en-us</language>
        <lastBuildDate>Sun, 02 Mar 2014 1:29 pm AEDT</lastBuildDate>
        <ttl>60</ttl>
        <yweather:location city="Melbourne" country="Australia" region="VIC"/>
        <yweather:units distance="km" pressure="mb" speed="km/h" temperature="C"/>
        <yweather:wind chill="21" direction="190" speed="19.31"/>
        <yweather:atmosphere humidity="46" pressure="1015.92" rising="0" visibility="9.99"/>
        <yweather:astronomy sunrise="7:03 am" sunset="7:57 pm"/>
        <image>
            <title>Yahoo! Weather</title>
            <width>142</width>
            <height>18</height>
            <link>http://weather.yahoo.com</link>
            <url>http://l.yimg.com/a/i/brand/purplelogo//uh/us/news-wea.gif</url>
        </image>
        <item>
            <title>Conditions for Melbourne, AU at 1:29 pm AEDT</title>
            <geo:lat>-37.87</geo:lat>
            <geo:long>145.1</geo:long>
            <link>http://us.rd.yahoo.com/dailynews/rss/weather/Melbourne__AU/*http://weather.yahoo.com/forecast/ASXX0075_c.html</link>
            <pubDate>Sun, 02 Mar 2014 1:29 pm AEDT</pubDate>
            <yweather:condition code="28" date="Sun, 02 Mar 2014 1:29 pm AEDT" temp="21" text="Mostly Cloudy"/>
            <description><![CDATA[
<img src="http://l.yimg.com/a/i/us/we/52/28.gif"/><br />
<b>Current Conditions:</b><br />
Mostly Cloudy, 21 C<BR />
<BR /><b>Forecast:</b><BR />
Sun - AM Clouds/PM Sun. High: 22 Low: 12<br />
Mon - Partly Cloudy. High: 27 Low: 14<br />
Tue - Mostly Sunny. High: 32 Low: 19<br />
Wed - AM Light Rain. High: 21 Low: 12<br />
Thu - Partly Cloudy. High: 22 Low: 13<br />
<br />
<a href="http://us.rd.yahoo.com/dailynews/rss/weather/Melbourne__AU/*http://weather.yahoo.com/forecast/ASXX0075_c.html">Full Forecast at Yahoo! Weather</a><BR/><BR/>
(provided by <a href="http://www.weather.com" >The Weather Channel</a>)<br/>
]]></description>
            <yweather:forecast code="30" date="2 Mar 2014" day="Sun" high="22" low="12" text="AM Clouds/PM Sun"/>
            <yweather:forecast code="30" date="3 Mar 2014" day="Mon" high="27" low="14" text="Partly Cloudy"/>
            <yweather:forecast code="34" date="4 Mar 2014" day="Tue" high="32" low="19" text="Mostly Sunny"/>
            <yweather:forecast code="11" date="5 Mar 2014" day="Wed" high="21" low="12" text="AM Light Rain"/>
            <yweather:forecast code="30" date="6 Mar 2014" day="Thu" high="22" low="13" text="Partly Cloudy"/>
            <guid isPermaLink="false">ASXX0075_2014_03_06_7_00_AEDT</guid>
        </item>
    </channel>
</rss><!-- fan516.sports.gq1.yahoo.com Sun Mar  2 03:08:38 PST 2014 -->

Round about here I thought to myself, there's simply no way I'm even going to try and parse that, not when there are APIs available to not only read the content, but also to query it.

So I wrote this quick test...

Which reads the RSS feed, finds the description element from the /rss/channel/item path, which contains the information you're after.

I then need to parse the description content, as it was in HTML format, this made it easy to find the img tag and extract the src attribute to the image.

Finally I displayed a JOptionPane showing the icon...

import java.awt.image.BufferedImage;
import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.URL;
import javax.imageio.ImageIO;
import javax.swing.ImageIcon;
import javax.swing.JOptionPane;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathConstants;
import javax.xml.xpath.XPathExpression;
import javax.xml.xpath.XPathExpressionException;
import javax.xml.xpath.XPathFactory;
import org.w3c.dom.Document;
import org.w3c.dom.Node;
import org.xml.sax.SAXException;

public class YahooTest {

    public static void main(String[] args) {
        Document doc = null;
        try {
            URL url = new URL("http://weather.yahooapis.com/forecastrss?w=1103816&u=c");
            Node descNode = getNodeFrom(url, "/rss/channel/item/description");

            if (descNode != null) {

                String desc = descNode.getTextContent();
                System.out.println(desc);

                desc = "<root>" + desc + "</root>";
                Node imgSourceNode = getNodeFrom(desc, "/root/img[@src]");
                if (imgSourceNode != null) {
                    String imgUrl = imgSourceNode.getAttributes().getNamedItem("src").getNodeValue();
                    BufferedImage img = ImageIO.read(new URL(imgUrl));
                    JOptionPane.showMessageDialog(
                                    null,
                                    "The Weather looks like...",
                                    "Weather",
                                    JOptionPane.PLAIN_MESSAGE,
                                    new ImageIcon(img));
                } else {
                    JOptionPane.showMessageDialog(null, "No image source found in description");
                }

            } else {
                JOptionPane.showMessageDialog(null, "No description node found");
            }           
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }

    public static Node getNodeFrom(URL url, String query) throws IOException, SAXException, ParserConfigurationException, XPathExpressionException {

        Node node = null;
        InputStream is = null;
        try {
            is = url.openStream();
            node = getNodeFrom(is, query);
        } finally {
            try {
                is.close();
            } catch (Exception e) {
            }
        }

        return node;

    }

    public static Node getNodeFrom(String text, String query) throws IOException, SAXException, ParserConfigurationException, XPathExpressionException {

        Node node = null;
        InputStream is = null;
        try {
            is = new ByteArrayInputStream(text.getBytes());
            node = getNodeFrom(is, query);
        } finally {
            try {
                is.close();
            } catch (Exception e) {
            }
        }

        return node;

    }

    public static Node getNodeFrom(InputStream is, String query) throws ParserConfigurationException, SAXException, IOException, XPathExpressionException {
        Document doc = DocumentBuilderFactory.newInstance().newDocumentBuilder().parse(is);
        return getNodeFrom(doc, query);
    }

    public static Node getNodeFrom(Document doc, String query) throws XPathExpressionException {
        return getNodeFrom(doc.getDocumentElement(), query);
    }

    public static Node getNodeFrom(Node node, String query) throws XPathExpressionException {
        XPath xPath = XPathFactory.newInstance().newXPath();
        XPathExpression xExp = xPath.compile(query);
        return (Node) xExp.evaluate(node, XPathConstants.NODE);
    }

}

I did spend some time looking through your code, but your poor variable naming choices made it next to near impossible to figure out what was going on...

Take a look at http://docs.oracle.com/javase/tutorial/jaxp/, How XPath Works and XPath Tutorial