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Commit 1733a1a4 authored by Goik Martin's avatar Goik Martin
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Better HTTP response handling, using Java streams

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Doc/Sda1/dom.xml
+ 50
− 46
View file @ 1733a1a4
......@@ -1560,22 +1560,27 @@ public class DomXpath {
<programlisting language="xml"
xml:id="domCheckImageAccessibility">&lt;!DOCTYPE html&gt;
&lt;html xmlns="http://www.w3.org/1999/xhtml"&gt;
&lt;head&gt; ... &lt;/head&gt;
&lt;html xmlns="http://www.w3.org/1999/xhtml"&gt;
&lt;head&gt;
&lt;title&gt;External Pictures&lt;/title&gt;
&lt;/head&gt;
&lt;body&gt;
&lt;h1&gt;External Pictures&lt;/h1&gt;
&lt;p&gt;A local image reference:&lt;img src="inline.gif" alt="none"/&gt;&lt;/p&gt;
&lt;p&gt;What about ftp?&lt;img src="ftp://inexistent.com/q.png" alt="none"/&gt;&lt;/p&gt;
&lt;table&gt;
&lt;tbody&gt;
&lt;tr&gt;
&lt;td&gt;An existing picture:&lt;/td&gt;
&lt;td&gt;&lt;img
src="http://www.hdm-stuttgart.de/bilder_navigation/laptop.gif"
alt="none"/&gt;&lt;/td&gt;
&lt;td&gt;&lt;img
src="https://www.hdm-stuttgart.de/bilder_navigation/laptop.gif"
alt="none"/&gt;&lt;/td&gt;
&lt;/tr&gt;
&lt;tr&gt;
&lt;td&gt;A non-existing picture:&lt;/td&gt;
&lt;td&gt;&lt;img src="<emphasis role="bold">http://www.hdm-stuttgart.de/rotfl.gif</emphasis>" alt="none"/&gt;&lt;/td&gt;
&lt;td&gt;&lt;img
src="http://www.hdm-stuttgart.de/rotfl.gif"
alt="none"/&gt;&lt;/td&gt;
&lt;/tr&gt;
&lt;/tbody&gt;
&lt;/table&gt;
......@@ -1586,51 +1591,40 @@ public class DomXpath {
<abbrev
xlink:href="http://www.ietf.org/rfc/rfc1738.txt">URL</abbrev>
image references to <emphasis>external</emphasis> Servers
starting either with <code>http://</code> ,
<code>https://</code> or <code>ftp://</code> ignoring other
protocol types. Internal image references referring to the
<quote>current</quote> server typically look like <code>&lt;img
src="/images/test.gif"</code>. So in order to distinguish these
two types of references we may use the XSL built in function
<link
starting either with <code>http://</code> or
<code>https://</code> ignoring other protocol types. Internal
image references referring to the <quote>current</quote> server
typically look like <code>&lt;img src="/images/test.gif"</code>.
So in order to distinguish these two types of references we may
use the XSL built in function <link
xlink:href="http://www.cafeconleche.org/books/bible2/chapters/ch17.html">starts-with()</link>
testing for the <code>http</code> or <code>ftp</code> protocol
testing for the <code>http</code> or <code>https</code> protocol
definition part of an <abbrev
xlink:href="http://www.ietf.org/rfc/rfc1738.txt">URL</abbrev>. A
possible output for the example being given is:</para>
<programlisting language="none">Received 'sun.awt.image.URLImageSource' from
http://www.hdm-stuttgart.de/bilder_navigation/laptop.gif
Unable to open 'http://www.hdm-stuttgart.de/rotfl.gif'</programlisting>
<programlisting language="none">xpath.CheckUrl (CheckUrl.java:51) - Protocol 'ftp' not yet implemented
ftp://inexistent.com/q.png, HTTP Status: null
https://www.hdm-stuttgart.de/bilder_navigation/laptop.gif, HTTP Status: OK
http://www.hdm-stuttgart.de/rotfl.gif, HTTP Status: Found</programlisting>
<para>The following code snippet shows a helpful class method to
check for both correctness of <abbrev
xlink:href="http://www.ietf.org/rfc/rfc1738.txt">URL</abbrev>'s
and accessibility of referenced objects:</para>
<para>Do not forget to provide unit tests at least for the image
network accessibility part.</para>
<programlisting language="java">package dom.xpath;
...
public class CheckUrl {
public static void checkReadability(final String urlRef) {
try {
final URL url = new URL(urlRef);
try {
final Object imgCandidate = url.getContent();
if (null == imgCandidate) {
System.err.println("Unable to open '" + urlRef + "'");
} else {
System.out.println("Received '"
+ imgCandidate.getClass().getName() + "' from "
+ urlRef);
}
} catch (IOException e) {
System.err.println("Unable to open '" + urlRef + "'");
}
} catch (MalformedURLException e) {
System.err.println("Adress '" + urlRef + "' is malformed");
}
}
}</programlisting>
<caution>
<para>Notice the response code for
<uri>http://www.hdm-stuttgart.de/rotfl.gif</uri>: This
resource is actually unavailable! But the web server tries to
recover by redirecting to an error page. Moreover a web server
may decide to return misleading response codes if deciding
your user agent is unable to handle the content type in
question. You may catch a glimpse of related problems by
reading <link
xlink:href="http://stackoverflow.com/questions/1378199/how-to-check-if-a-url-exists-or-returns-404-with-java">How
to check if a URL exists or returns 404 with Java?</link>. For
the current exercise we will not dig deeper into the
subject.</para>
</caution>
<tip>
<para>Using XPath expressions in conjunction with namespaces
......@@ -1649,6 +1643,15 @@ public class CheckUrl {
xlink:href="http://www.jdom.org/pipermail/jdom-interest/2012-May/016850.html">XPath
examples</link></para>
</listitem>
<listitem>
<para>For analyzing the accessibility of referenced <xref
linkend="glo_HTTP"/> / <acronym>HTTPS</acronym> resources
see the previously mentioned discussion in <link
xlink:href="http://stackoverflow.com/questions/1378199/how-to-check-if-a-url-exists-or-returns-404-with-java">How
to check if a URL exists or returns 404 with
Java?</link>.</para>
</listitem>
</itemizedlist>
</tip>
</question>
......@@ -1687,8 +1690,9 @@ public class CheckUrl {
<xref linkend="glo_XHTML"/> namespace. We thus create a
corresponding <classname
xlink:href="http://www.jdom.org/docs/apidocs/org/jdom2/Namespace.html">Namespace</classname>
instance along with the desired <code>xhtml</code>
prefix:</para>
instance handling the desired one to one correspondence between
the <code>"xhtml"</code> prefix and our target namespace
<uri>http://www.w3.org/1999/xhtml</uri>:</para>
<programlisting language="java">final Namespace htmlNamespace = // This will allow for XPath
Namespace.getNamespace("xhtml", // expressions like xhtml:img
......
P/Sda1/VerifyImgAccess/src/main/resources/fileextref.html → P/Sda1/VerifyImgAccess/fileextref.html
+ 2
− 8
View file @ 1733a1a4
<?xml version="1.0"?>
<!--
The pre- html-5 way:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"
"http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
-->
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>External Pictures</title>
</head>
<body>
<h1>External Pictures</h1>
<p>A local image reference:<img src="inline.gif" alt="none"/></p>
<p>What about ftp?<img src="ftp://inexistent.com/q.png" alt="none"/></p>
<table>
<tbody>
<tr>
<td>An existing picture:</td>
<td><img
src="http://www.hdm-stuttgart.de/bilder_navigation/laptop.gif"
src="https://www.hdm-stuttgart.de/bilder_navigation/laptop.gif"
alt="none"/></td>
</tr>
<tr>
......
P/Sda1/VerifyImgAccess/pom.xml
+ 8
− 0
View file @ 1733a1a4
......@@ -33,5 +33,13 @@
<version>${jaxen.jaxen.version}</version>
</dependency>
<!-- HTTP/HTTPS response codes -->
<dependency>
<groupId>javax</groupId>
<artifactId>javaee-api</artifactId>
<version>7.0</version>
</dependency>
</dependencies>
</project>
P/Sda1/VerifyImgAccess/src/main/java/dom/xpath/CheckExtImage.java
+ 10
− 8
View file @ 1733a1a4
package dom.xpath;
import java.io.IOException;
import java.util.List;
import org.jdom2.Document;
import org.jdom2.Element;
......@@ -28,18 +27,21 @@ public class CheckExtImage {
public void process(final String xhtmlFilename) throws JDOMException, IOException {
final Document htmlInput = builder.build(xhtmlFilename);
final Namespace htmlNamespace = // This will allow for XPath expressions like xhtml:img
Namespace.getNamespace("xhtml", "http://www.w3.org/1999/xhtml");
final XPathExpression<Element> xpath = XPathFactory.instance().compile (
"//xhtml:img[starts-with(@src, 'http://') or starts-with(@src, 'https://') or starts-with(@src, 'ftp://')]",
new ElementFilter(), null, htmlNamespace);
final List<Element> images = xpath.evaluate (htmlInput);
for (final Element image: images) {
CheckUrl.checkReadability(image.getAttributeValue("src"));
}
xpath.evaluate(htmlInput).stream().
map(img -> img.getAttributeValue("src")).
forEach(CheckExtImage::printResult);
}
static private void printResult(String url) {
System.out.println(url
+ ", HTTP Status: " + CheckUrl.checkReadability(url));
}
}
\ No newline at end of file
P/Sda1/VerifyImgAccess/src/main/java/dom/xpath/CheckExtImageDriver.java
+ 1
− 1
View file @ 1733a1a4
......@@ -12,6 +12,6 @@ public class CheckExtImageDriver {
*/
public static void main(String[] argv) throws Exception {
final CheckExtImage ao = new CheckExtImage();
ao.process("src/main/resources/fileextref.html");
ao.process("fileextref.html");
}
}
\ No newline at end of file
P/Sda1/VerifyImgAccess/src/main/java/dom/xpath/CheckUrl.java
+ 32
− 12
View file @ 1733a1a4
package dom.xpath;
import java.io.IOException;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import javax.ws.rs.core.Response;
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
/** Check Readability of a given URL
* @author $Author: goik $
* @version $Rev: 290 $ $Date: 2007-11-19 17:49:15 +0100 (Mo, 19. Nov 2007) $
......@@ -12,28 +19,41 @@ import java.net.URL;
*
*/
public class CheckUrl {
static private final Logger log = LogManager.getLogger(CheckUrl.class);
/** Check whether a given object like http://someserver.com/img.gif
* can be retrieved.
*
* @param urlRef
* The URL to be checked for read access
*
* @return An informative URL related status message or null e.g. if the protocol in question is unknown.
*/
public static void checkReadability(final String urlRef) {
public static Response.Status checkReadability(final String urlRef) {
try {
final URL url = new URL(urlRef);
try {
final Object imgCandidate = url.getContent();
if (null == imgCandidate) {
System.err.println("Unable to open '" + urlRef + "'");
} else {
System.out.println("Received '"
+ imgCandidate.getClass().getName() + "' from "
+ urlRef);
}
} catch (IOException e) {
System.err.println("Unable to open '" + urlRef + "'");
switch(url.getProtocol()) {
case "http":
case "https":
try {
final HttpURLConnection huc = (HttpURLConnection) url.openConnection();
huc.setRequestMethod("GET");
huc.connect();
return Response.Status.fromStatusCode(huc.getResponseCode());
} catch (final IOException e) {
log.error("Unable to connect to " + urlRef, e);
}
break;
default:
log.error("Protocol '" + url.getProtocol() + "' not yet implemented");
}
} catch (MalformedURLException e) {
System.err.println("Adress '" + urlRef + "' is malformed");
}
return null;
}
}
\ No newline at end of file
P/Sda1/VerifyImgAccess/src/main/resources/log4j2.xml
+ 2
− 2
View file @ 1733a1a4
......@@ -11,10 +11,10 @@
<Loggers>
<!-- You my want to define class or package level per-logger rules -->
<Logger name="de.hdm_stuttgart.mi.sda1.alignimg.App" level="warn">
<Logger name="de.hdm_stuttgart.mi.sda1.alignimg.App" level="debug">
<AppenderRef ref="A1"/>
</Logger>
<Root level="warn">
<Root level="debug">
<AppenderRef ref="STDOUT"/>
</Root>
</Loggers>
......
P/Sda1/VerifyImgAccess/src/test/java/alignimg/TestImgSearch.java
+ 21
− 8
View file @ 1733a1a4
package alignimg;
import java.io.IOException;
import javax.xml.parsers.ParserConfigurationException;
import javax.ws.rs.core.Response;
import org.junit.Assert;
import org.junit.Test;
import org.xml.sax.SAXException;
import dom.xpath.CheckUrl;
/**
*
*/
public class TestImgSearch {
/**
*/
@Test
public void searchAlignImageElements() throws ParserConfigurationException,
SAXException, IOException {
public void findExistingImage() {
Assert.assertTrue(Response.Status.OK ==
CheckUrl.checkReadability(
"https://www.hdm-stuttgart.de/bilder_navigation/laptop.gif"));
}
/**
*/
@Test
public void findRedirectErrorPage() {
Assert.assertTrue(Response.Status.FOUND ==
CheckUrl.checkReadability(
"http://www.hdm-stuttgart.de/rotfl.gif"));
}
}
\ No newline at end of file
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