Archive for September, 2009

Debugging GUI events

September 22nd, 2009

Warning: count(): Parameter must be an array or an object that implements Countable in /www/webvol14/yj/kljuhyzt1cwiiug/ on line 76

Debugging gui events is usually not possible with regular line per line debugging and is done mostly by tracing.
For debugging code that relies on Java swing events like drag and drop, mouse moving, etc., having something similar to code below is very useful:

public boolean isMouseAboveHeaderPanel() {
System.out.println("HeaderPanel.isMouseAboveHeaderPanel() called from: "
+ Thread.currentThread().getStackTrace()[2].getClassName() + "."
+ Thread.currentThread().getStackTrace()[2].getMethodName());
// ...

In this way you trace not only current function but also you got information from where you entered that function. Of course to make things easier you should make some kind of a shortcut for entering this trace line. In Eclipse you can do that with code template:

System.out.println("${enclosing_type}.${enclosing_method}() called from: "
+ Thread.currentThread().getStackTrace()[2].getClassName() + "." 
+ Thread.currentThread().getStackTrace()[2].getMethodName());

This helped me in lot of situations, I hope that it will help you as well.


General, Java , ,

Groovy blob and mysql

September 20th, 2009

In certain occasions e.g. when you want to save scrapped html page or just a specific part of it (e.g. div with its contents) the recommendation I found is to use the blob type and save xml document as binary stream.

In groovy, this is achieved in a rather simple way:

class Document {
  int id
  String title
  String xmlContent
Sql sql = Sql.newInstance(
          "user", "pass", "com.mysql.jdbc.Driver")
// We assume db table similar to:
      `id` bigint(32) NOT NULL AUTO_INCREMENT,
      `title` varchar(500) NOT NULL,
      `xmlContent` blob,
      PRIMARY KEY (`id`)
def saveDocuments(def docs) {
  println "Saving documents to database..."
  def documents = sql.dataSet("document")
  docs.each {Document doc ->
    documents.add(title: doc.title, xmlContent: doc.xmlContent)

When you want to retrieve data, with Groovy this is not much complicated either:

def loadDocuments() {
  def list = []
  sql.eachRow("SELECT * FROM document") {
    Document doc = new Document(it.toRowResult())
    if (it['xmlContent'] != null) {
      doc.xmlContent = new String(it['xmlContent'])
  println "Loaded ${list.size()} documents from database"

I tried the code with mysql database but I assume that you can achieve the same with any other database.

One hint for mysql blobs and utf-8: although utf-8 charset behaves very well with other database table fields (if you add useUnicode=true and characterEncoding=UTF-8 parameters to your connection string), in order to work with utf-8  blob fields you should adjust one more parameter: useBlobToStoreUTF8OutsideBMP=true. With this parameter set, your utf8 encoded xml documents will behave well with mysql database.


groovy, Java , , ,