Make a Map from a list, perl style

Make a Map from a varargs list. Useful for iBatis parameterClass objects.

Populate a DTO with mock data

Problem:
Every so often i need to have a list of some simple DTOs in order to build a screen. The DTOs need to be populated from the database, but the query is not ready. Its somewhat painful to write dummy data creation methods over and over again.

Solution:
Using Groovy(though not required), Spring and a bit of reflection i cover most of the simple DTOs.



To use, pass the class a list of which you expect

foreach to iterate over a map in 1.5

When you iterate over a map you need to usually get the key and the value, use this to get them both without having to use the key to get the value!

<br />for (Map.Entry<String, String> entry : hashmap.entrySet()){<br /> String key = entry.getKey();<br /> String val = entry.getValue();<br />}<br />

This also happens to not raise any unchecked warnings which you would have to @SuppressWarnings("unchecked")

Custom tags: passing in maps or other datatypes that arent strings

problem:
I needed to pass a hashmap into a custom tag. This hashmap was to be created on the jsp page using jstl, and then passed into the tag as an attribute.
For some reason i was not able to find the solution with just one google query.

solution:
1. first, to create a hashmap on the jsp using jstl and add some stuff to it:
<br /><jsp:useBean id="something" class="java.util.HashMap"><br /> <c:set target="${something}" property="name1" value="value1"/><br /> <c:set target="${something}" property="name-2" value="blee"/><br /></jsp:useBean><br />

2. next, add another attribute to your tag in the tld file:
<br /><attribute><br /> <name>someName</name><br /> <required>false</required><br /> <rtexprvalue>true</rtexprvalue><br /> <type>java.util.Map</type><br /></attribute><br />

3. finally, pass the hashmap into your tag .. <tag someName="${something}" /> and make sure that the setter in the tag takes in a Map

obfuscated java code sample

This piece of java code compiles and runs. It is the most obfuscated java snippet i've ever seen.




requires java 1.5

appfuse 1.8.1 ehcache NoSuchMethodError

Problem:
I installed appfuse-light-all 1.8.1, installed acegi security, and ajax. After doing a build i get the following error when Spring starts up:

Error creating bean with name 'userManager' defined in ServletContext resource [/WEB-INF/applicationContext.xml]
.... bunch of other errors ...
Invocation of init method failed; nested exception is java.lang.NoSuchMethodError: net.sf.ehcache.Cache.<init>

Solution:
The problem here is that i am using an older version of ehcache for some reason. Doing a bit more digging shows that i have the following versions of ehcache in my M2 repository:
[M2_REPO]/net/sf/ehcache/ehcache/1.2.3/
[M2_REPO]/net/sf/ehcache/ehcache/1.3.0/

version 1.2.3 is what is messing things up for me, it gets loaded by Spring first and causes the error. Deleting that directory does not work because "ant deploy" does the following if the dependency is missing:

Buildfile: build.xml
[artifact:dependencies] Downloading: net/sf/ehcache/ehcache/1.2.3/ehcache-1.2.3.jar
[artifact:dependencies] Downloading: net/sf/ehcache/ehcache/1.2.3/ehcache-1.2.3.jar

Now, since i dont know how to use MAVEN, i cant remove the code that fetches the old version, so i do the evil hack to prevent it from being created:

remove the directory "1.2.3", make a copy of "1.3.0" directory, call it "1.2.3". rename all the files inside to say 1.3.0 instead of 1.2.3.

Also, if you are deploying to tomcat as a directory, you might need to go into the webapps directory in tomcat, locate your app, and its WEB-INF and delete ehcache-1.2.3.jar thats is probably there now.

Now you can use appfuse.

if anyone knows of a better way to solve this, leave a comment.

Teamsite DCR java parser

Working with teamsite DCRs is painful. This is my attempt to make it a little bit less painful.

I made this program in order to make it easier to edit and parse teamsite data capture records. I should have done this a long time ago, and actually this is the first step towards freeing myself from OpenDeploy.

Anyway, here is the code for the parser:

<br />package com.dogself.teamsite.parser;<br /><br />import java.io.File;<br />import java.io.FileInputStream;<br />import java.io.FileOutputStream;<br />import java.io.IOException;<br />import java.util.ArrayList;<br />import java.util.List;<br /><br />import org.jdom.Document;<br />import org.jdom.Element;<br />import org.jdom.JDOMException;<br />import org.jdom.input.SAXBuilder;<br />import org.jdom.output.XMLOutputter;<br />import org.jdom.xpath.XPath;<br /><br />/**<br /> * Utility to open interwoven teamsite DCRs, access the values of all the items, and update item values.<br /> * <br /> * Note: replicant support is not yet implemented!<br /> * @author koryakm<br /> *<br /> */<br />public class DCRParser {<br /> private String path;<br /> private Document dom;<br /> <br /> public DCRParser(String path){<br /> this.path = path;<br /> try {<br /> parse();<br /> } catch (JDOMException e) {<br /> e.printStackTrace();<br /> } catch (IOException e) {<br /> e.printStackTrace();<br /> }<br /> }<br /> /**<br /> * return all the values of the given item as text<br /> * @param name = name of the item to get<br /> * @return<br /> * @throws JDOMException <br /> */<br /> @SuppressWarnings("unchecked")<br /> public ArrayList<string> getItemText(String name) throws JDOMException{<br /> XPath xpath = XPath.newInstance("//item[@name='"+name+"']/value"); <br /> ArrayList<string> arr = new ArrayList<string>(); <br /> List<element> nodes = xpath.selectNodes(dom);<br /> for(Element node: nodes){<br /> arr.add(node.getText());<br /> }<br /> return arr;<br /> }<br /> <br /> /**<br /> * Get all of the items named 'name' - returns a collection of DOM elements, you can change their values<br /> * in order to modify the original xml<br /> * @param name<br /> * @return<br /> * @throws JDOMException<br /> */<br /> @SuppressWarnings("unchecked")<br /> public ArrayList<element> getItem(String name) throws JDOMException{<br /> XPath xpath = XPath.newInstance("//item[@name='"+name+"']/value"); <br /> return new ArrayList<element>(xpath.selectNodes(dom));<br /> }<br /> /**<br /> * <br /> * @param xpath<br /> * @return<br /> * @throws JDOMException<br /> */<br /> @SuppressWarnings("unchecked")<br /> public ArrayList<element> getByXPath(String xpath) throws JDOMException{<br /> XPath xp = XPath.newInstance(xpath); <br /> return new ArrayList<element>(xp.selectNodes(dom));<br /> }<br /> <br /> /**<br /> * get an item using a path like this /main/item1/ (sorta like in formAPI)<br /> * @param path<br /> * @return<br /> * @throws JDOMException<br /> */<br /> @SuppressWarnings("unchecked")<br /> public ArrayList<element> getItemByPath(String path) throws JDOMException{<br /> String[] parts = path.split("/");<br /> String exp = "record";<br /> for(String p: parts){<br /> if(p.length()==0) continue;<br /> exp += "/item[@name='"+p+"']/value";<br /> }<br /> XPath xpath = XPath.newInstance(exp); <br /> return new ArrayList<element>(xpath.selectNodes(dom));<br /> }<br /> <br /> /**<br /> * proprietery: get uid of the DCR<br /> * @return<br /> * @throws JDOMException<br /> */<br /> public String getUID() throws JDOMException{<br /> return getItemByPath("/main/uid").get(0).getText();<br /> }<br /> /**<br /> * save this DCR<br /> * @throws IOException<br /> */<br /> public void saveDCR() throws IOException{<br /> saveDCR(path);<br /> }<br /> /**<br /> * save this DCR "as"<br /> * @param path<br /> * @throws IOException<br /> */<br /> public void saveDCR(String path) throws IOException{<br /> File f = new File(path);<br /> if(!f.exists()) f.createNewFile();<br /> FileOutputStream out = new FileOutputStream(f);<br /> XMLOutputter outputter = new XMLOutputter();<br /> try {<br /> outputter.output(dom, out); <br /> }<br /> catch (IOException e) {<br /> e.printStackTrace();<br /> }<br /> }<br /> private void parse() throws JDOMException, IOException{<br /> FileInputStream in = new FileInputStream(path); <br /> SAXBuilder builder = new SAXBuilder(); <br /> dom = builder.build(in); <br /> } <br />}<br />

Note: The code above does not yet truly support replicants, as in, you cant say 'give me the 3rd text field from the 2nd replicant..' unless you can figure out the xpath for it, which somewhat defeats the purpose of having a DCR parser.


Here is a driver class that uses my parser in order to do something silly.

<br />package com.dogself.teamsite.parser;<br /><br />import java.io.File;<br />import java.io.IOException;<br />import java.util.ArrayList;<br />import java.util.Arrays;<br /><br />import org.jdom.Element;<br />import org.jdom.JDOMException;<br /><br />public class Driver {<br /><br /> public Driver(String root) throws JDOMException, IOException{<br /> File[] files = getAllFilesUnderDir(root, true);<br /> for(File f: files){<br /> DCRParser parser = new DCRParser(f.getAbsolutePath());<br /> //get the title element (i know there is only 1)<br /> Element title = parser.getItem("txtTitle").get(0);<br /> String text = title.getText();<br /> //remove all html tags from the title<br /> text = text.replaceAll("<[^>]+>", "");<br /> //fix stupidness<br /> text = text.replaceAll("®", "&reg;");<br /> title.setText(text);<br /> parser.saveDCR();//save changes<br /> System.out.println("fixed title in:"+f.getAbsolutePath());<br /> }<br /> }<br /> public static void main(String[] args) {<br /> try {<br /> Driver d = new Driver("z:/test");<br /> } catch (JDOMException e) {<br /> e.printStackTrace();<br /> } catch (IOException e) {<br /> // TODO Auto-generated catch block<br /> e.printStackTrace();<br /> }<br /> }<br /> <br /> @SuppressWarnings("unchecked")<br /> public static File[] getAllFilesUnderDir(String fullpath, boolean recursive) {<br /> ArrayList queue = new ArrayList(10);<br /> ArrayList matched = new ArrayList();<br /> File root = new File(fullpath);<br /> File[] files = root.listFiles();<br /> if (files == null || files.length == 0) {<br /> return new File[] {};<br /> }<br /> queue.addAll(Arrays.asList(files));<br /> for (int j = 0; j < child =" (File)" files =" child.listFiles();"> 0)?((File[]) matched.toArray(new File[] {})):(new File[] {});<br /> }<br />}<br /><br />

in order to use this parser you will need the following libs:
- JDOM
- JAXEN

Java: reading / writing international characters

It is actually very easy to support international characters in java. The only trick is knowing the charset that the text is encoded in. Most of the time is a safe bet to try UTF-8 if you dont know. If you use Apache's HTTPClient it has methods to get the charset of the stream you are reading from.


<br />//to open the file for reading:<br />BufferedReader read = new BufferedReader(new InputStreamReader(new FileInputStream(file), Charset.forName("UTF8")));<br />//to open file for writing:<br />BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(file), Charset.forName("UTF8")));<br />

regex to split a document into words

Say you wanted to split a document into words, but works like are'nt shouldnt be split on the ' and numbers like 10,004,333 should remain intact, but other punctuation should be removed from the resulting word array.

A good way to do this is using Scanner's findWithinHorizon and a regular expression. This way you dont need to read the entire document into memory before processing it.

<br />Pattern p = Pattern.compile("[A-Za-z]+(?:['-][A-Za-z]+)?|\\d+(?:[,.]\\d+)?");<br />Scanner sc = new Scanner(new File("/path/to/the/file.txt"));<br />String word = null;<br />while ((word = sc.findWithinHorizon(p, 0)) != null)<br />{<br /> // etc.<br />}<br />

Java: Understanding Weak References

The other day i was reading programming at reddit and stumbled on this article:
Understanding Weak References which was a good read but i still had some questions, so i turned to Java Developer Forums for help. I didnt get flamed! (much). What i got was a very good response from a user named kdgregory which is note-to-dogself worthy.

My questions are in blue boxes:

If weak references are great at stopping leaks, why not use them all the time?

They're great at stopping leaks in the situation where you're attaching data to an object that (should) have a limited lifetime. If you used a regular map (most likely an IdentityHashMap), you'd be creating a strong reference to the object via the map, so it would never be collected, even when there are no other references to it (I call this a leak, other people don't).

For example, ThreadLocal uses weak references, because they'll be cleared when the thread ends.

ObjectOutputStream should use weak references (and a changed protocol) so that it can be used in long-running conversations without constantly calling reset(). But it doesn't.

"WeakHashMap works exactly like HashMap, except that the keys (not the values!) are referred to using weak references."

• does this imply that hashmap stores values in weak refs, if so, why?

• should i use WeakHashMap for tasks where i will have another reference to objects i put into the map. ie i dont put my only ref into this map?

No, HashMap doesn't use weak references for either key or value. The author's wording (and for that matter, the JDK JavaDoc wording) is a little misleading.

One typical use for weak references is in a canonicalizing map to reduce memory consumption with duplicated data. With such a map, you would store an object as both key and value, and retrieve the canonical value when presented with an arbitrary key -- think String.intern(). However, you can't use WeakHashMap to do this without wrapping the value in a weak reference also.

When do i not use weak references ?

Most of the time. Any reference object means that you have to access your original object in two steps (have to call get() on the reference) rather than just one. And normally, you'd know the lifetime of your objects.

extract links using htmlparser

i have come to realize that even though i love to do everything in regex, extracting links with regex is not really the best idea.

the best idea is to use htmlparser to extract the links.

This code sniplet will extract links from a page body, and given the link where the body was found it will resolve the relative links. This is tailored to be used by a crawler.

<br />public static Collection<String> retrieveLinks(String url, byte[] body, String charSet) {<br /><br /> Collection<String> result = new ArrayList<String>();<br /> <br /> URI uriLink;<br /> try {<br /> uriLink = new URI(url);//url of the body<br /> String st = new String(body, charSet);<br /> Parser parser = new Parser();<br /> parser.setInputHTML(st);<br /> NodeList list = parser.extractAllNodesThatMatch(new NodeClassFilter (LinkTag.class));<br /> for (int i = 0; i < list.size (); i++){<br /> LinkTag extracted = (LinkTag)list.elementAt(i);<br /> <br /> if(!extracted.isHTTPLikeLink()) continue; //ignore mailto / javascript and other weird protocol links<br /> <br /> <br /> String extractedLink = extracted.extractLink().replaceAll("&", "&");//we need to unescape these<br /> <br /> extractedLink = extractedLink.replaceAll(" ","%20");//URI class doesnt like spaces in URLs, but content creators dont care.. :P<br /> extractedLink = extractedLink.trim();//URI will barf on a link that look like "foo.com "<br /> if(extractedLink.length() == 0) continue; // i am betting that a link that looks like "" is user error. with our url scheme, it most certainly is.. <br /> if(extractedLink.startsWith("#")) continue; //skip all anchors, they are useless to a crawler<br /> if(extractedLink.matches("(?i)^javascript:.*"))continue; //HTMLParser thinks anything but lower case 'javascript:' is a non-js link<br /> <br /> URI uriRelative = new URI(extractedLink);<br /> //System.out.println("i:"+i);<br /> URI resolved = uriLink.resolve(uriRelative);<br /> //linkfilter will return true if crawling from <br /> //url --> resolvedUrl<br /> //is allowed by some rules<br /> String link = resolved.toString();<br /> //here we should check if the link is acceptable.<br /> result.add(link);<br /> <br /> }<br /> }<br /> } catch (URISyntaxException e) {<br /> // TODO: this is a bad link, log this!<br /> log.info("Bad Link Syntax on page:["+url+"] BAD LINK:"+e.getMessage());<br /> } catch (UnsupportedEncodingException e) {<br /> // TODO Auto-generated catch block<br /> e.printStackTrace();<br /> } catch (ParserException e) {<br /> // TODO Auto-generated catch block<br /> e.printStackTrace();<br /> } <br /> <br /> return result;<br /> }<br />

extract links from a webpage

this is useful if you decide to make a web crawler, and dont want to bother with an html parser. You have to read the body of the page into a string, and then use this regex to extract all the links.

supported link types: <img src=...<a href=...
<br /><br />String body = "..."; //body of the page<br />Matcher m = Pattern.compile("(?im)(?:(?:(?:href)|(?:src))[ ]*?=[ ]*?[\"'])(((?:http|https)(?::\\/{2}[\\w]+)(?:[\\/|\\.]?)(?:[^\\s\"]*))|((?:\\/{0,1}[\\w\\.]+)+))[\"']").matcher(body);<br />while(m.find()){<br />String absolute = m.group(2);<br />String relative = m.group(3);<br />}<br />

an absolute url is in the form of "http://something.com/blah"
a relative url is in the form of "/something/path.blee"

now you can figure out what to do with these...

Remove HTML tags regex

when using an HTML parser is too much work, you may want to use a small regex to remove all the html tags

this is java:
<br />String output = input.replaceAll("</?\\w++[^>]*+>", "");<br />

Using EL in custom tags as attributes

Problem:
I was working on a custom tag and i needed to pass it a bean from a JSP page kind of like this:
<customtag var="${somebean.something.else}">
I realized that what i was getting inside my custom tag was a String, not my bean.

Solution:
You need to use the ExpressionEvaluator to evaluate the expression, and get the bean, here is the code i used in my SimpleTag: (i was getting a Date object by the way)

<br /><br />ExpressionEvaluator eval = getJspContext().getExpressionEvaluator();<br />Date date = null;<br />//dateVar this is the EL expression<br />try { //this thing here resolves the date expression into a java object!<br /> date = (Date)eval.evaluate(dateVar, Date.class, getJspContext().getVariableResolver(), new FunctionMapper(){<br />public Method resolveFunction(String arg0, String arg1) {<br /> return null; //i couldnt figure out how to get a FunctionMapper from somewhere...<br />}<br /> });<br />} catch (ELException e1) {<br /> throw new JspException(e1);<br />}<br />


Edit Aug 7, 2008:
It has come to my attention that in jsp 2.0 the EL expressions are evaluated before being passed to the custom tags, so you dont need to do any of this crap anymore.

How To: Implement RMI from scratch

The java.lang.reflect.Proxy class will let you provide an arbitrary implementation for an interface.

So, start with that on the client. Figure out how to produce a factory for interface objects. Understand how the proxy invocation works.

Then, create a socket connection to the server. Wrap it with an ObjectInputStream/ObjectOutputStream.

Now you need to define a protocol between client and server. For example, let's say that the client sends an integer object ID, followed by a method name, followed by an array of parameters. The server needs to find the object, and invoke the appropriate method. Then it needs to send the result back to the client.

Then you can get into distributed GC ...

source: java dev forums

NoClassDefFoundError: com/sun/mail/util/SharedByteArrayInputStream

problem:
when trying to send mail i get error: NoClassDefFoundError: com/sun/mail/util/SharedByteArrayInputStream

solution:
get mail.jar and put it on your classpath

http://java.sun.com/products/javamail/downloads/index.html

Java: find nested balanced tags

Problem:
I needed to parse out some divs from a html page, and java's regex cant do it. atleast when you have arbitrary number of nested balanced elements.

Solution:
<br /><br />private String removeDivContents(String id, String clazz,<br /> String text){<br />String div = "<div class="\"><br /> +clazz.toLowerCase()+"\" id=\""+id.toLowerCase()+"\">";<br />String textl = text.toLowerCase();<br />int index = textl.indexOf(div);<br />if(index == -1){<br /> return text;<br />}<br />int loc = index + div.length();<br />int end = findBalancedClosingTag(loc, textl,<br /> "<div","</div>", 1);<br />return text.substring(0,index) + text.substring(end);<br />}<br /><br />private int findBalancedClosingTag(int start,<br />String textl, String startTag, String endTag, int unClosedStarts){<br />int index = textl.indexOf(endTag,start);<br />if(index == -1){<br /> return start;<br />}<br />Pattern p = Pattern.compile(startTag);<br />Matcher m = p.matcher(textl.substring(start, index));<br />unClosedStarts --; // we are in this function so we closed ONE start tag<br />while(m.find()){<br /> unClosedStarts ++;<br />}<br />if(unClosedStarts == 0){<br /> return index + endTag.length();<br />} else {<br /> return findBalancedClosingTag(index + endTag.length(), textl, startTag, endTag, unClosedStarts);<br />}<br />}<br />
Use at your own risk.

nice regex util class, replaceAll

elliotth.blogspot.com/java-implementation-of-rubys-gsub.html

Here is an example of what this does:

String result = new Rewriter("([0-9]+) US cents") {
public String replacement() {
  long dollars = Long.parseLong(group(1))/100;
     return "$" + dollars;
  }
}.rewrite("5000 US cents");
System.out.println(result);

prints>> $50

nice!

Unsupported major.minor version 48.0

Problem:
Unsupported major.minor version 48.0

solution:
what you are running was compiled on 1.4 and you are running 1.3 or older

Problem: MANIFEST.MF missing class-path inside JAR

Problem:
MANIFEST.MF missing class-path: inside JAR.

Solution:
Put a blank like at the end of the manifest file.