info.michael-simons.eu

The dangers of Javas ImageIO

Michael — Wed, 25 Jan 2012 07:52:11 +0000

Javas ImageIO works… well, most of the time. It contains some unfixed, jpeg related bugs, but it works.

It may contain some dangers when used in a webbased application for generation large images on the fly.

Most problems are related to ImageIOs filed based caching and not flushing buffers when an IOException in an underlying stream occurs.

First, the javax.imageio.ImageReader. It caches some data in files. It is essential to dispose the reader and the underlying ImageInputStream after use if it’s not needed anymore like so:

if(imageReader.getInput() != null && imageReader.getInput() instanceof ImageInputStream)			
  ((ImageInputStream)imageReader.getInput()).close();
imageReader.dispose();

If it isn’t closed and disposed, the temporary cache files are either deleted not at all or maybe at the next garbage collection. I was able to bring down a VM by “java.io.FileNotFoundException: (Too many open files)” several times because i didn’t close a reader in a loop. Even the classloader wasn’t able to load any new classes after the ImageReader going mad on the file handle.

The other side is the javax.imageio.ImageWriter. There is an issue mentioned in the Tomcat Wiki.

I used the ImageWriter to dynamically create large images. I directly passed the javax.servlet.ServletOutputStream to the ImageWriter. If the generation of images takes long enough, there’s a good chance that the client aborts the request and the ServletOutputStream gets flushed right when the ImageWriter is writing to it. I didn’t have the exceptions mentioned in the wiki but my VM crashed. Great. I guess it had something to do with the native org.apache.coyote.ajp.AjpAprProtocol Ajp Apr connector i use, but that’s just guessing.

I solved this problem by using a temporary file and its related outputstream which i then stream like described here. This solution is not only faster but i also can catch any exception related to an aborting client.

Also take care to dispose the write as well like so:

try {
	 imageWriter.setOutput(out);
	 imageWriter.write(null, new IIOImage(image, null, null), iwp);
	 out.flush();
 } catch(IOException e) {                        
	 imageWriter.abort();                    
	 throw e;
 } finally {
	 try {                           
		 out.close();                            
	 } catch(Exception inner) {                              
	 }
	 imageWriter.dispose();
 }

This took me several hours to figure out… I hope someone finds this post useful.

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Optimizing web resources with wro4j, Spring and ehcache

Michael — Wed, 18 Jan 2012 10:18:11 +0000

I think that almost no website today can do without JavaScript. There are some incredible good JavaScript libraries like jQuery for which an enormous mass of plugins and extensions exits.

The downside of this is, that for example the JavaScript code of my daily picture project Daily Fratze is bigger than the whole startpage of my first “homepage” was.

With every problem there is a solution, namely JavaScript compressors and minifier. Those tools can compress the code by removing superfluous whitespaces, renaming variables and functions or even by optimizing the code.

So far i have used the YUI compressor maven mojo in my Spring based projects. This is a build time solution that compresses JavaScript and CSS files when creating a war file.

For me it had several disadvantages: I don’t see the effect of compressing when i develop my application and it could not concatenate multiple script files.

The later is important because every additional request a browser makes slows down the loading of a webpage. And manual hacking all JavaScript into one file? No way…

wro4j to the rescue:

Free and Open Source Java project which brings together almost all the modern web tools: JsHint, CssLint, JsMin, Google Closure compressor, YUI Compressor, UglifyJs, Dojo Shrinksafe, Css Variables Support, JSON Compression, Less, Sass, CoffeeScript and much more. In the same time, the aim is to keep it as simple as possible and as extensible as possible in order to be easily adapted to application specific needs.

My goal was to integrate wro4j with Spring and ehcache with a minimum number of additional configuration files.

If you’re interested in some of my ideas, read on:

Please note: This is not the complete solution. The wro.xml is missing as well as some of my infrastructure ideas. But you should get the idea on how to use wro4j with Spring, extend it with your own caching strategy and configure the processors.

First step: Creating a WroFilter implementation that doesn’t depend on wro.properties:

import java.util.Map;
import java.util.Properties;
 
import ro.isdc.wro.http.ConfigurableWroFilter;
import ro.isdc.wro.manager.factory.WroManagerFactory;
 
public class Wro4jFilter extends ConfigurableWroFilter {
	private final WroManagerFactory factory;
 
	public Wro4jFilter(final Map<String, String> properties, final WroManagerFactory wroManagerFactory, final boolean debug) {
		this.factory = wroManagerFactory;
 
		final Properties p = new Properties();
		p.putAll(properties);
		p.put("debug", Boolean.toString(debug));				
		super.setProperties(p);		
	}
 
	@Override
	protected WroManagerFactory newWroManagerFactory() {		
		return this.factory;
	}	
}

As you see this filter accepts a map that is converted to a properties instance from which the superclass is configured. I also inject the WroManagerFactory which will be my interface to ehcache. Finally i can overwrite the debug flag.

This bean is instantiated through an @Configuration class like so:

@Configuration
@Profile("prod")
public class WebConfigProd extends WebConfig {
	@Bean(name="wroFilter")
	@Override
	public Filter getWroFilter() {
		return new Wro4jFilter(super.defaultWroProperties, new Wro4jManagerFactory(super.cacheManager), false);
	}
}

The defaultWroProperties is a Map created from the Spring Environment so that i can keep my wro4j options in my application properties file. cacheManager is an instance of net.sf.ehcache.CacheManager. The CacheManager is needed for my own WroManagerFactory which you'll see later.

To use this filter you need the Spring DelegatinFilterProxy:

>
	>webResourceOptimizer>
	>org.springframework.web.filter.DelegatingFilterProxy>
	>
		>targetBeanName>
		>wroFilter>
	>    	
	>
		>targetFilterLifecycle>
		>true>    	
	>
 >

Having set the targetFilterLifecycle to true is actually essential because the original ro.isdc.wro.http.WroFilter relies on the init method.

So far i only have the filter. What's missing is the wro4j model. This is where groups of JavaScript and CSS files are defined and it can be - among others - an xml file. I want mine to reside with my other configuration files in an dedicated package. To accomplish that i've created a special WroManagerFactory:

import java.io.InputStream;
 
import net.sf.ehcache.CacheManager;
import ro.isdc.wro.cache.CacheEntry;
import ro.isdc.wro.cache.CacheStrategy;
import ro.isdc.wro.cache.ContentHashEntry;
import ro.isdc.wro.extensions.processor.css.YUICssCompressorProcessor;
import ro.isdc.wro.extensions.processor.js.GoogleClosureCompressorProcessor;
import ro.isdc.wro.manager.factory.BaseWroManagerFactory;
import ro.isdc.wro.model.factory.WroModelFactory;
import ro.isdc.wro.model.factory.XmlModelFactory;
import ro.isdc.wro.model.resource.processor.factory.ProcessorsFactory;
import ro.isdc.wro.model.resource.processor.factory.SimpleProcessorsFactory;
import ro.isdc.wro.model.resource.processor.impl.css.CssUrlRewritingProcessor;
 
import com.google.javascript.jscomp.CompilationLevel;
 
public class Wro4jManagerFactory extends BaseWroManagerFactory {
	public final static String CACHE_NAME = "some_cache_name";
	private final CacheManager cacheManager;
 
	public Wro4jManagerFactory(CacheManager cacheManager) {
		this.cacheManager = cacheManager;
	}
 
	@Override
	protected ProcessorsFactory newProcessorsFactory() {
		final SimpleProcessorsFactory rv = new SimpleProcessorsFactory();
                // URLs in CSS needs to be rewritten as it is served from a different location than the original files. I'm not using @import statements, otherwise the appropriate processor should be added for rewriting them as well
		rv.addPreProcessor(new CssUrlRewritingProcessor());	
                // JavaScript compression by the Google Closure compressor	
		rv.addPreProcessor(new GoogleClosureCompressorProcessor(CompilationLevel.SIMPLE_OPTIMIZATIONS));
                // And css by YUI Css Compressor
		rv.addPreProcessor(new YUICssCompressorProcessor());
		return rv;
	}			
 
	@Override
	protected WroModelFactory newModelFactory() {
		return new XmlModelFactory() {
			@Override
			protected InputStream getModelResourceAsStream() {
				return this.getClass().getResourceAsStream("/foo/bar/config/wro.xml");
			}
		};
	}	
 
	@Override
	protected CacheStrategy<CacheEntry, ContentHashEntry> newCacheStrategy() {
		return new Wro4jCacheStrategy<CacheEntry, ContentHashEntry>(this.cacheManager.getCache(CACHE_NAME));
	}	
}

The location of my wro model is handled in newModelFactory. Nothing special. What's more interesting is newCacheStrategy. It get's an ehcache net.sf.ehcache.Cache from the CacheManager and passes it to my caching strategy:

import net.sf.ehcache.Cache;
import net.sf.ehcache.Element;
import ro.isdc.wro.cache.CacheStrategy;
 
public class Wro4jCacheStrategy<K, V> implements CacheStrategy<K, V> {	
	private final Cache cache;
 
	public Wro4jCacheStrategy(Cache cache) {
		this.cache = cache;
	}
 
	@Override
	public synchronized void put(K key, V value) {
		this.cache.put(new Element(key, value, null, null, null));
	}
 
	@SuppressWarnings("unchecked")
	@Override
	public synchronized V get(K key) {
		final Element element = this.cache.get(key);		
		return (V) (element == null ? null : element.getValue());
	}
 
	@Override
	public synchronized void clear() {
		this.cache.removeAll();
	}
 
	@Override
	public synchronized void destroy() {
		this.clear();
	}
}

So far i have:

No need for wro.properties
The wro.xml model along with my other configuration files
The WroFilter initialized by Spring
Having ehcache cache my compressed and concatenated resources

As you might have guessed there is also a WebConfigDev. The development configurations sets wro4j to development mode which means i can turn of minimisation at runtime through an url parameter like so "?minimize=false".

I didn't want to change my jsps all the time so i defined a bean that holds a property minimizeResources that is changable via JMX. I include my JavaScript like so:

 name="script">
	 name="src">
		 value="/wro/project.js">
			 name="minimize">${globalOptions.minimizeResources}>
		>
	>
	 />
>

CSS is analog. I use the jsp:element syntax because all my jsps are actually jspx files.

With this solution i can easily turn off minimization in development mode.

In production mode i now have one compressed JavaScript file instead of 15 files and one CSS file instead of four. The first request takes a second or so but the compressed (and gzipped) content is cached. The Google Closure is actually pretty awesome and reduces my accumulated JavaScript code by over 50%.

Reducing the number of requests necessary had - for me - the biggest impact on my smartphone.

I really can recommend wro4j. It's very extensible and actually pretty easy to use. I cannot only be used to compress files but also can allow you to use CoffeeScript or SASS in Spring or JEE application.

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Creating a CSRF protection with Spring 3.1

Michael — Wed, 11 Jan 2012 09:37:58 +0000

CSRF Attacks still seems to be a problem, a pity that there is no standard solution in the Spring 3.1 framework. Although not probably, i wanted to protect my projects by malicious crafted links.

I didn’t want to use an extra library but something which is already available in the Spring framework. Here is what i come up with:

I choose the token protection mechanism for my implementation.

The core of my solution is the CSRFToken Service:

public interface CSRFTokenService {
	public final static String TOKEN_PARAMETER_NAME = "_tk";
 
	public final static String TOKEN_ATTRIBUTE_NAME = "CSRFToken";
 
	public final static List<String> METHODS_TO_CHECK = Collections.unmodifiableList(Arrays.asList("POST", "PUT", "DELETE"));
 
	/** Generates a new CSRF Protection token */
	public String generateToken();
 
	/** Obtains the token from the session. If there is no token, a new one will be generated */
	public String getTokenFromSession(final HttpServletRequest request);
 
	/** This method tests, if a token is acceptable when a user is logged in */
	public boolean acceptsTokenIn(HttpServletRequest request);
}

import java.security.SecureRandom;
 
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;
 
import org.apache.commons.codec.binary.Base64;
import org.apache.commons.lang.StringUtils;
import org.springframework.stereotype.Service;
 
import de.dailyfratze.services.CSRFTokenService;
 
@Service("csrfTokenService")
public class CSRFTokenServiceImpl implements CSRFTokenService {
	private final SecureRandom random = new SecureRandom();
 
	@Override
	public String generateToken() {
		final byte[] bytes = new byte[32];
		random.nextBytes(bytes);
		return Base64.encodeBase64URLSafeString(bytes);
	}
 
	@Override
	public String getTokenFromSession(final HttpServletRequest request) {
		return request.getUserPrincipal() == null ? null : this.getTokenFromSessionImpl(request.getSession(false));
	}
 
	private String getTokenFromSessionImpl(final HttpSession session) {
		String token = null;
 
		if(session != null) {
			token = (String) session.getAttribute(TOKEN_ATTRIBUTE_NAME);
			if(StringUtils.isBlank(token))
				session.setAttribute(TOKEN_ATTRIBUTE_NAME, (token = generateToken()));
		}
		return token;
	}
 
	@Override
	public boolean acceptsTokenIn(HttpServletRequest request) {
		boolean rv = false;
 
		// Token is only verified if principal is not null
		if(request.getUserPrincipal() == null) 
			rv = true;
		else {
			final HttpSession session = request.getSession(false);
			rv = session != null && this.getTokenFromSessionImpl(session).equals(request.getParameter(TOKEN_PARAMETER_NAME));
		}
		return rv;
	}
}

“getTokenFromSession” is called right after a user logs in, so that the token gets stored into his session.

As you can see in the implementation of “acceptsTokenIn”, the token is only needed and verified when the principal is not null, meaning when a user is authenticated.

The interface contains some constants: The name of the token in forms and requests and the name of the attribute under which the token is stored in the session. The token itself is just a base64 of some random bytes.

I only want the token to be checked in writing methods: METHODS_TO_CHECK, meaning only in put, delete and posts requests. My applications don’t change state based on get requests.

So where to check for the token? I use a pretty simple Spring “HandlerInterceptor”:

package de.dailyfratze.controller;
 
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
 
import org.apache.commons.lang.StringUtils;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;
 
import de.dailyfratze.services.CSRFTokenService;
 
public class CSRFInterceptor implements HandlerInterceptor { 
	@Autowired
	private CSRFTokenService csrfTokenService;
 
	@Override
	public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
		boolean rv = true;
		if(CSRFTokenService.METHODS_TO_CHECK.contains(StringUtils.defaultIfBlank(request.getMethod(), "").toUpperCase()) && !csrfTokenService.acceptsTokenIn(request)) {
			response.addHeader("X-DailyFratze-InvalidCSRFToken", Boolean.toString(true));
			response.sendError(HttpServletResponse.SC_FORBIDDEN);
			rv = false;
		} 		
		return rv;
	}
 
	@Override
	public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {	
	}
 
	@Override
	public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {		
	}		
}

This interceptor stops the chain if the request method should be checked and the token is not acceptable by sending a HTTP forbidden error. The additional response header is used by Ajax calls to present a dialog that the session is invalidated.

How to get the token into forms? I wanted to be able to change the token name in only one place so i came up with the following custom tag:

import java.io.IOException;
 
import javax.servlet.http.HttpServletRequest;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.TagSupport;
 
import org.apache.commons.lang.StringUtils;
 
import de.dailyfratze.services.CSRFTokenService;
import de.dailyfratze.utils.HelperRegistry;
 
/**
 * Creates a hidden input field with the CSRF Token
 * @author michael.simons, 2011-09-20
 */
public class CSRFTokenTag extends TagSupport {
	private static final long serialVersionUID = 745177955805541350L;
 
	private boolean plainToken = false;
 
	@Override
	public int doStartTag() throws JspException {
		final CSRFTokenService csrfTokenService = HelperRegistry.getHelper(super.pageContext.getServletContext(), super.pageContext.getRequest(), CSRFTokenService.class, "csrfTokenService");
		final String token = csrfTokenService.getTokenFromSession((HttpServletRequest) super.pageContext.getRequest());
		if(!StringUtils.isBlank(token))
			try {
				if(plainToken)
					pageContext.getOut().write(token);
				else
					pageContext.getOut().write(String.format("\"hidden\" name=\"%1$s\" id=\"%1$s\" value=\"%2$s\" />", CSRFTokenService.TOKEN_PARAMETER_NAME, token));
			} catch (IOException e) {
			}
		return SKIP_BODY;
	}
 
	@Override
	public int doEndTag() throws JspException {
		return EVAL_PAGE;
	}
 
	public boolean isPlainToken() {
		return plainToken;
	}
 
	public void setPlainToken(boolean plainToken) {
		this.plainToken = plainToken;
	}
 
	public static String getTokenParameterName() {
		return CSRFTokenService.TOKEN_PARAMETER_NAME;
	}
}

with the corresponding mapping:

 version="1.0" encoding="UTF-8" ?>
 xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-jsptaglibrary_2_1.xsd"
	version="2.1">
	>1.0>
	>df>
	>http://michael-simons.eu/taglibs/df>
	>
		>csrfToken>
		>de.dailyfratze.tags.CSRFTokenTag>
		>empty>
		>
			>plainToken>
			>false>	
		>
	>	
	>
		>csrfTokenParameter>
		>de.dailyfratze.tags.CSRFTokenTag>
		>java.lang.String getTokenParameterName()>
	>
>

I can use this tag in forms like so:

Or for generating url parameters for example for ajax calls like so:

So if a token is invalid, the user is either redirect to an error page if it is a normal post, ajax calls through jQuery can be handled like so:

function isInvalidCSRFToken = function(xhr) {
	var rv = false;
	if(xhr.status == 403 && xhr.getResponseHeader('X-DailyFratze-InvalidCSRFToken') == 'true') {			
		alert($('Session is invalid').text());
		rv = true;
	}
	return rv;
}
 
$.ajax({
	type: 'post',
	url: theUrl,	
	dataType: 'text',		
	complete: function(xhr, status) {
		if(isInvalidCSRFToken(xhr))	    				
			return;	    				
		// handle the result
	} 	        
});

The code snippets are all taken from a running project. If you want to use them, use them. The package names are missing and must be added. Also the JavaScript code isn’t complete.

Feel free to comment, if you have suggestions, remarks or anything else. Also, if you can use this, i’d be happy to hear from you.

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Mac OS X Lion loses network connection after sleep

Michael — Thu, 05 Jan 2012 15:53:03 +0000

Sleep related problems have never been a problem for me with OS X (at least the sleep of the machine) since Lion.

Sleep works perfectly fine but after wake my machine has no internet connection anymore, at least it looks like this. It’s only domains that aren’t resolved anymore. It also affects wired and wifi networks. There are a lot of threads in the Apple forums that blame USB drives, Optical drives and the like but this sounds a bit like voodoo.

I found the following working solution:

Edit “/System/Library/LaunchDaemons/com.apple.mDNSResponder.plist” like so:

 version="1.0" encoding="UTF-8"?>

 version="1.0">
>
	>Label>
	>com.apple.mDNSResponder>
	>OnDemand>
	/>
	>UserName>
	>_mdnsresponder>
	>GroupName>
	>_mdnsresponder>
	>ProgramArguments>
	>
		>/usr/sbin/mDNSResponder>
		>-launchd>
		>-AlwaysAppendSearchDomains>
		>-DisableSleepProxyClient>		
	>
	>MachServices>
	>
		>com.apple.mDNSResponder>
		/>
	>
	>Sockets>
	>
		>Listeners>
		>
			>SockFamily>
			>Unix>
			>SockPathName>
			>/var/run/mDNSResponder>
			>SockPathMode>
			>438>
		>
	>
	>EnableTransactions>
	/>
>
>

and relaunch the mDNSResponder like so:

sudo launchctl unload -w /System/Library/LaunchDaemons/com.apple.mDNSResponder.plist 
sudo launchctl load -w /System/Library/LaunchDaemons/com.apple.mDNSResponder.plist

This fixes to things: The domain resolution described here and the 2 hourly automatic wake from sleep described here.

Update:

It seems that fixed the problem just for that one time. To fix it every wake i use “SleepWatcher” by . Installed as said in the read me, save this file somewhere as restart_mDNSResponder

#!/bin/bash
killall -HUP mDNSResponder

and copy this

<?xml version="1.0" encoding="UTF-8"?>
DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
        <key>Labelkey>
        <string>de.bernhard-baehr.sleepwatcherstring>
        <key>ProgramArgumentskey>
        <array>
                <string>/usr/local/sbin/sleepwatcherstring>
                <string>-Vstring>
                <string>-w /path/to/restart_mDNSResponderstring>
        array>
        <key>RunAtLoadkey>
        <true/>
        <key>KeepAlivekey>
        <true/>
dict>
plist>

to /Library/LaunchDaemons/de.bernhard-baehr.sleepwatcher-20compatibility.plist.

and execute

sudo launchctl load -w /Library/LaunchDaemons/de.bernhard-baehr.sleepwatcher-20compatibility.plist

This did the trick for me.

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Git snippets

Michael — Thu, 22 Dec 2011 20:11:36 +0000

These are a view things that i had looked up to solve some problems and i plan to update this post regularly…

To push a new branch to remote

git push origin new_branch

To delete a remote branch

git push origin :new_branch

To push new tags

git push --tags origin

To delete a remote tag

git tag -d 12345
git push origin :refs/tags/12345

To reset a local branch to exactly match a remote branch

git fetch origin
git reset --hard origin/master

To abort a rebase

git rebase --abort

Changing the origin of your git repository (relocate the repository)

git config remote.origin.url [new origin url]

Last update: 2012/01/04

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oEmbedding twitter updates with Java and WordPress

Michael — Tue, 20 Dec 2011 11:48:34 +0000

I’m really a big fan of oEmbed. My project Daily Fratze acts as oEmbed provider and consumer for example.

Now I’m really happy that twitter announced that it now acts as an oembed provider:

Introducing the statuses/oembed endpoint: dev.twitter.com/docs/api/1/get… ^TS

— Twitter API (@twitterapi) Dezember 8, 2011

(I’d even be happier if twitter would autodiscover providers )

To use this in a Java based application you can use my java-oembed lib with the following configuration:

Oembed oembed = new OembedBuilder(this.httpClient)
	.withCacheManager(cacheManager)
	.withBaseUri("http://yourproject")
	.withConsumer("yourproject")
	.withProviders(					
			new OembedProviderBuilder()
				.withName("twitter")
				.withFormat("json")
				.withMaxWidth(480)
				.withEndpoint("https://api.twitter.com/1/statuses/oembed.%{format}")
				.withUrlSchemes("https?://twitter.com/#!/[a-z0-9_]{1,20}/status/\\d+")
				.build()
	 )
	.withHandlers(new CommonHandler("twitter"))
	.build();

The handler looks like this:

import org.apache.commons.lang.StringEscapeUtils;
import org.jsoup.nodes.Document;
import org.jsoup.nodes.Element;
 
import ac.simons.oembed.OembedResponse;
import ac.simons.oembed.OembedResponseHandler;
 
 
public class CommonHandler implements OembedResponseHandler {
	private String handlerFor;
 
	public CommonHandler(String handlerFor) {
		this.handlerFor = handlerFor;
	}
 
	@Override
	public String getFor() {
		return handlerFor;
	}
 
	@Override
	public void handle(Document document, Element a, OembedResponse response) {
		final StringBuilder hlp = new StringBuilder();
 
		final String title = StringEscapeUtils.escapeHtml(response.getTitle());
		if(response.getType().equalsIgnoreCase("video") || response.getType().equalsIgnoreCase("rich")) {
			hlp.append("\"display:block; text-align:center;\">");
			hlp.append(response.getHtml());
			hlp.append("");
		} else if(response.getType().equalsIgnoreCase("photo")) {			
			hlp.append("\"display:block; text-align:center;\">");			
			hlp.append(String.format("\"%s\" alt=\"%s\" title=\"%s\" style=\"width: %d; height: %d;\" />", response.getUrl(), title, title, response.getWidth(), response.getHeight()));			
			hlp.append("");
		}
 
		a.before(hlp.toString());
		a.remove();		
	}
}

Be careful to get the latest release, twitter has some real large values for cache ages and i needed to update a member from int to long.

To have WordPress automatically embed statusupdates, add the following line to the “functions.php” of your current theme. Create the file if it isn’t available in the root folder of your theme:

wp_oembed_add_provider('#https?://twitter.com/\#!/[a-z0-9_]{1,20}/status/\d+#i', 'https://api.twitter.com/1/statuses/oembed.json', true);

Whenever you add the plain link (whithout an anchor tag) to a statusupdate on a single line in a post, it will be embedded like the example above.

Update

If you are more into plugins, just download my Enable Twitter oEmbed WordPress plugin, install it and you’re good to go.

An alternative to oEmbed for Twitter was the Twitter Blackbird Pie Plugin for WordPress, but why adding more stuff if everything else is already there? My plugin is much more lightweight.

Embedding me looks like this, by the way:

the picture will always show my latest update on daily fratze.

As this is probably the last post here for this year, i wish every visitor some nice christmas holidays!

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Scripted network mounts with Windows

Michael — Mon, 12 Dec 2011 09:05:23 +0000

I have some services and scheduled tasks that call a Batch file under windows. The scheduled tasks cannot access network drives that the assigned user has defined, but luckily there is a “mount” pendant within Windows as well.

To mount a network share within the Batch script use:

net use t: \\server\share /persistent:no

The authentication is taken from the user that is assigned to the task.

If this not enough use

net use t: \\server\share /persistent:no /user:user@domain password

To unmount the share use

net use t: /delete

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Java stuff

Michael — Mon, 28 Nov 2011 09:32:00 +0000

Here is some Java stuff I’ve written over the last year for Daily Fratze. All of the stuff is in use on Daily Fratze since June 2011.

java-akismet: java-akismet is a simple client for Akismet based on the latest version of Apache HttpComponents.
java-oembed: I really like the idea of oEmbed: A mechanism for auto embedding stuff from other sites so that users don’t have to paste some html code into a textbox but just plain links. This is my version of a configurable Java client that can autodetect oEmbed endpoints as well as statically configured endpoints.
java-autolinker: This is my idea of an autolinker based on jsoup. If you want to get autolinking right, you have to parse the text. Just scanning for regex that matches urls or email addresses is not enough. This autolinker first parses the text into a DOM tree and passes all text nodes to the configured linkers. At the moment it supports URLs, email addresses and twitter handles.

I’d be happy if someone can actually use this stuff too or even contribute to it

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Fixing hibernate “Cannot release connection” exception using DBCP and MySQL.

Michael — Mon, 21 Nov 2011 08:04:34 +0000

Every 8 hours i got a Hibernate exception “Cannot release connection” within a Java application using Hibernate, Apache DBCP on Tomcat:

org.hibernate.exception.GenericJDBCException: Cannot release connection
    at org.hibernate.exception.SQLStateConverter.handledNonSpecificException(SQLStateConverter.java:103)
    at org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:91)
    at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:43)
    at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:29)
    ..
    ..
Caused by: java.sql.SQLException: Already closed.

Not only that the messages polluted my inbox, the exception was visible to the enduser, resulting in a HTTP 500 error. An older blog post i found suggested dismissing DBCP and using c3p0, a solution that i’m not quite found of. At least, the post helped to reproduce the problem within my development setup. The underlying problem was indeed the MySQL wait_timeout.

There’s quite a long documentation on the Tomcat JDBC Connection Pool. Although the Tomcat team recommends their own solution since Tomcat 7, i still wanted to go with DBCP.

The relevant keywords are “testOnBorrow”, “testOnReturn”, “testWhileIdle”, “validationQuery” and “timeBetweenEvictionRunsMillis”. The first 3 are boolean values. If set to true, the query given as validationQuery is executed on borrowing a connection from the pool, on returning or when idling. The first option is not an option on production use as the query is executed before each call. Although “Select 1″ is probably very fast, i just don’t want to have. Also: The problem is an invalidated, idle connection so i set testWhileIdle to true. And what happened? Nothing! The problem stayed. So there is the last option timeBetweenEvictionRunsMillis which should, according to the docs, default to 5 seconds but it doesn’t. The documentation is wrong. It’s under zero, so the eviction thread that tests idle connections never run. I’ve tweeted the tomcat team, but there was no reaction.

So the correct configuration for a DBCP pool database source is:


	type="javax.sql.DataSource"
	driverClassName="com.mysql.jdbc.Driver"
	maxActive="100"
	maxIdle="30"
	maxWait="10000"
	testOnBorrow="false"
	testOnReturn="false"
	testWhileIdle="true"
	validationQuery="Select 1"
	timeBetweenEvictionRunsMillis="1800000"
/>

This way the eviction thread runs every 30 minutes, testing idle connections with the query “Select 1″ and removing them from the pool. The timeBetweenEvictionRunsMillis should not be to low. It should be adapted to the configured MySQL wait_timeout.

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Old and tired?

Michael — Wed, 09 Nov 2011 07:19:45 +0000

Right now i’m at the #jaxcon in Munich. While sitting in a talk, this tweet by @cuchulin caught my attention:

#wjax// #jaxcon People seems like java itself: They are getting older and look somehow tired.

— erhard karger (@cuchulin) November 8, 2011

I really don’t think that’s Java who’s old and tired, neither as a language nor an ecosystem. It’s the people, who not only are looking tired but who are. Well, at least, I am.

I’m a curious person and always eager to learn new stuff but the last 3, 4 years the learning process and the stream of new tools, techniques, frameworks and other stuff accelerated even more than it did in the transition from client/server development to multi-tier-architectures 10 years ago.

At each conference there are new tools. New tools to “get things done”, new paradigms to organize your work and new tools to create stuff. It’s getting real hard to choose and if you want to get your head around the full stack, you’ve plenty of stuff to try, read and experiment on.

The last 2 years saw the coming of so many new languages. Some will vanish, some will stay, but it’s for sure: Another field of learning.

Given that situation plus the stream of information we get the whole day now (tweets, g+, facebook and more) it’s a tiring situation. Most of the people in the talks sit in front of their laptops or have an iPad and are constantly checking twitter and the like. Who wouldn’t be tired?

I really appreciated Adam Beans Talk “Just developed” yesterday. We really need to focus more on the things we want to create and to some extend less on the tools and methodologies.

On a personal note: I am tired. Not because of my “hard” family life with a 2-year-old, absolutely no. I just can’t really turn of my head anymore. The boundaries between work, home and spare time are diminishing. Most of the time it’s a good thing because i can spend more time at home with my family but on the other hand i have all the stuff to think about, to read and to try out often for the late evening and then they are to stay in my head.

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