Written on March 16, 2009 by Allan Lykke Christensen
For this weeks JSF tip, I’ll show you how to send binary data (such as a file) to the user by way of an action handler or listener.
Say, you want to generate a custom PDF and send it to the user as he clicks a link. You need a JSF page, and a backing bean.
Your JSF page may look like this:
<h:form>
<h:commandLink id="lnkDownload"
actionListener="#{myBean.onDownload}"
target="_blank"
value="Download PDF" />
</h:form>Your JSF backing bean may look like this:
public MyBean {
public void onDownload(ActionEvent event) {
try {
// here you need to get the byte[] representation of
// the file you want to send
byte[] binary_data = ;
String filename = "generated_file.pdf”;
FacesContext fctx = FacesContext.getCurrentInstance();
ExternalContext ectx = fctx.getExternalContext();
HttpServletResponse response = (HttpServletResponse) ectx.getResponse();
response.setHeader("Content-Disposition", "attachment; filename=\"" + filename + "\"");
response.setHeader("Content-Transfer-Encoding", "Binary");
response.setHeader("Pragma", "private");
response.setHeader("cache-control", "private, must-revalidate");
ServletOutputStream outs = response.getOutputStream();
outs.write(binary_data);
outs.flush();
outs.close();
response.flushBuffer();
fctx.responseComplete();
} catch (IOException ex) {
ex.printStackTrace();
}
}That’s it for today.
P.S. alternatively you can use this component which is less code intensive: http://kenai.com/projects/scales/pages/Download
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Written on March 9, 2009 by Allan Lykke Christensen
It has been a busy year so far. Every year I start out thinking that I really need to relax because the previous year was too hectic, but every year it ends up being much more hectic. Anyway, I thought I’d post a JSF quick time that might shave some headache for people developing internationalised applications.
Most JSF developers are aware of the resource-bundle tag in faces-config. Using this tag you can specify a resource bundle that should be available to all your pages using a given variable. For example, the code below will make a variable, msgs, available in all your pages without having to use the loadBundle tag.
<faces-config version="1.2">
...
<application>
<resource-bundle>
<base-name>my.class.path.Messages</base-name>
<var>msgs</var>
</resource-bundle>
</application>
...
</faces-config>So, say that Messages.properties contains the following:
HELLO_WHAT_IS_YOUR_NAME=Hello, what’s your name?
you can from any page reference this text by writing:
<h:outputText value=”#{mgs.HELLO_WHAT_IS_YOUR_NAME}” />or
<h:outputText value=”#{mgs[‘HELLO_WHAT_IS_YOUR_NAME’]}” />I prefer the former as my favourite IDE (NetBeans) support code completion for all the messages in a managed resource bundle.
So far so good. But what if you want to do something a bit more advanced, such as outputting “Hello Allan, welcome to my site. Your last visit was 7. February 2009 at 10:45”. You are not limited to static text in your resource bundle. You can provide placeholders for content that will be replaced at run-time. Let’s have a look at the Message.properties:
WELCOME_MESSAGE=Hello {0}, welcome to my site. Your last visit was {1,date,long} at {1,time,short}You’ll notice that the message is parameterised using two parameters. The first parameter we are expecting a string containing the name of the user, the second parameter is a java.util.Date containing both the date and time when user last visited the site. Notice that I’ve reused the second paramenter ({1}), one time for the date and the other for the time. On your JSF page you would use the message as follows (imaging that you have a bean called welcome containing a property for getting the name of the user and last visit):
<h:outputFormat value=”#{msgs.WELCOME_MESSAGE}”>
<f:param value=”#{welcome.userName}” />
<f:param value=”#{welcome.lastVisit}” />
</h:outputFormat>Pretty neat, eh?
What about the classical case of singular and plural messages? Imagine that you want to display the number of records in a table “There are 10 records in the table”. If the Message.properties contained:
RECORDS_IN_TABLE=There are {0} records in the tableYou’d end up an embarrassing problem if there was only one record in the table:
“There are 1 records in the table” (This sentence is grammatical incorrect)
Instead you would want it to output:
“There is 1 record in the table”
To do this, you have to use the choice pattern:
RECORDS_IN_TABLE=There {0, choice, 0#are|1#is|2#are} {0} {0, choice, 0#records|1#record|2#records}The format might look a bit awkward, but once you have understood the pattern it is simple:
{0,choice |
means, taking the first parameter and base the output on a choice of formats |
0#are |
if the first parameter contains 0 (or below), then it should print “are” |
|1#is |
or, if the first parameter contain 1, then it should print “is” |
|2#are} |
or, if the first parameter contains 2 (or above), then it should print “are” |
Now, that is nice! So let’s examine the output of these examples:
<h:outputFormat value=”#{msgs.RECORDS_IN_TABLE}”>
<f:param value=”#{0}” />
</h:outputFormat> |
There are 0 records in the table |
<h:outputFormat value=”#{msgs.RECORDS_IN_TABLE}”>
<f:param value=”#{1}” />
</h:outputFormat> |
There is 1 record in the table |
<h:outputFormat value=”#{msgs.RECORDS_IN_TABLE}”>
<f:param value=”#{2}” />
</h:outputFormat> |
There are 2 records in the table |
<h:outputFormat value=”#{msgs.RECORDS_IN_TABLE}”>
<f:param value=”#{10}” />
</h:outputFormat> |
There are 10 records in the table |
Enjoy!
Posted in Java | Comment Now!
Written on February 2, 2009 by Allan Lykke Christensen
Since mid last week I’ve been down with a terrible flu. It has been so bad that I haven’t been able to look at the computer screen (imagine that!!). To pass time I picked up a book that I picked up from Lulu.com a few months ago called “Getting Real — The smarter, faster, easier way to build a successful web application“. The authors behind the book are the developers behind 37signals (probably most known for developing the Ruby on Rails framework). The contents of the book is actually freely available from their website, but since I’m spending more and more time away from the computer these days I decided to buy a paper copy.
I absolutely loved the book. I knew that I would love the book when I read part of the disclaimer: “If our tone seems too known-it-allish, bear with us. We think it’s better to present ideas in bold strokes than to be wishy-washy about it. If that comes off as cocky or arrogant, so be it. We’d rather be provocative than water every down with “it depends…”“. It is so refreshing to read something that is written with confidence and not some generic advice that can mean everything and nothing.
The book takes you through the stages of launching a web application from staffing, to interface design, to pricing and post-launch activities. Each chapter deals with a specific stage of the launch and provide easy-to-read, snappy, no bull advices on how to go about the given stage. Although I don’t agree with everything in the book it is very enlighting, refreshing and entertaining. It reminds me a lot about the book “How to become a CEO- The Rules for Rising to the Top of Any Organization” by Jeffrey J Fox, which I can recommend for a quick entertaining read.
It’s a must read for everything developing web applications. I’ll give this book five stars out of five!!
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Written on January 8, 2009 by Allan Lykke Christensen
Another big shot goes bust! This time it’s the Indian IT “giant” Satyam (http://www.computing.co.uk/vnunet/news/2233443/satyam-chairman-admits-seven). This is not long after the Danish company; IT Factory, pulled a similar stunt (http://politiken.dk/newsinenglish/article605506.ece). I’m starting to think that when all things are going well, it’s just an illusion with a few puppet masters pulling all the strings. However, I just can’t believe that in both cases it is claimed that the auditors and board didn’t have any knowledge of the wrong doings. If this is true then we must be talking about the dumbest people in the world.
Posted in Commentary | Comment Now!
Written on January 2, 2009 by Allan Lykke Christensen
Just as the year was ended I got a great Christmas present from Sun Microsystems.
1) A cool NetBeans 10 year anniversary T-shirt for participating in the community acceptance test programme for NetBeans 6.5 (NetCAT)
2) A pass on my exam to become Sun Certified Specialist for NetBeans IDE
The exam was special to me as it was my first ever certification exam. My score was 82%, with the least score in questions about building Java SE applications. I guess it shows that I’ve never build Java SE applications on NetBeans. Otherwise I think the exam was great. Studying for the exam revealed a lot of useful features that I had never used before, but now wondering how I could ever live without. I can highly recommend doing the exam!
Thanks Sun!
Posted in Career, Java | Comment Now!
Written on December 31, 2008 by Allan Lykke Christensen
A thing that always annoys me about installing Java is that it doesn’t automatically set up the JAVA_HOME environment variable after installation. I guess this is to avoid having problems when you have multiple virtual machines installed. Anyway, I use Ubuntu Linux to host the majority of my Java Application Server. It is easy install Java (sudo apt-get install sun-java6-jdk) but there always seems to be a debate about where to set the JAVA_HOME environment variable. Some instructions say you should add it to your personal profile (e.g. ~/.bashrc) others suggest adding it to the global profile (i.e. /etc/profile), some people even suggest adding it directly in the init script for the services that need the variable. My suggest is to add an executable shell script to /etc/profile.d/ called javahome.sh. The content of the file would be: export JAVA_HOME=/usr/lib/jvm/java-6-sun. All shell scripts (i.e. executable files with the extension .sh) located in the /etc/profile.d/ directory are loaded upon login and would therefore work for all users without having to change system files that may change upon the next O/S upgrade. To test the script simply type source /etc/profile This will reload the profile for the current user. To verify that the environment variable has been initialised type export|grep JAVA_HOME
Enjoy!
Posted in Java, System administration | Comment Now!
Written on November 24, 2008 by Allan Lykke Christensen
If you have a custom converter or validator you may provide these with the option of letting developers specify attributes. For example, let’s say that we are creating a converter that will allow the formatting of a Calendar object. Note, that the <f:convertDateTime /> is for Date objects (which can be easily retrieved from a Calendar, but that is beside the point). So the custom converter I’ll create here is for converting/formatting Calendar objects.
package com.blogspot.bigallan.converters;
import java.text.*;
import java.util.*;
import javax.el.ValueExpression;
import javax.faces.component.UIComponent;
import javax.faces.context.FacesContext;
import javax.faces.convert.Converter;
public class CalendarConverter implements Converter {
/**
* Not implemented as the converter is one-way only.
*/
public Object getAsObject(FacesContext ctx, UIComponent component, String value) {
return null;
}
public String getAsString(FacesContext ctx, UIComponent component, Object value) {
// Get the Calendar to convert
Calendar calendar = (Calendar) value;
String pattern = "";
// Obtain attributes specified along with the converter
Map<String, Object> attributes = component.getAttributes();
// Check if the pattern attribute was specified
if (!attributes.containsKey("pattern")) {
System.out.println("pattern was not specified");
return "";
} else {
pattern = (String)attributes.get("pattern");
}
// Create a DateFormatter for the pattern
DateFormat outputFormat = new SimpleDateFormat(pattern);
// Format the calendar
try {
Date date = originalFormat.parse(calendar.getTime());
return outputFormat.format(originalDate));
} catch (ParseException ex) {
ex.printStackTrace();
return "";
}
}
}In faces-config.xml you would declare the converter like this:
<converter>
<converter-id>calendarConverter</converter-id>
<converter-class>com.blogspot.bigallan.converters.CalendarConverter</converter-class>
</converter>We can now use the converter in a view:
<h:outputText value="#{myBean.calendarObject}">
<f:converter converterId="calendarConverter" />
<f:attribute name="pattern" value="d. MMMM yyyy" />
</h:outputText>When the code is rendered in the browser you’ll get the calendar converter to something like this 24. November 2008. So far so good. However, what if we didn’t specify the date pattern as static text, but rather bind it to a value. This technique is efficient when you reuse the pattern in many places and want to keep the pattern in a central place. So say that we had a managed-bean called common with a method getDateFormat() : String that would provide the pattern. The code would look like this:
<h:outputText value="#{myBean.calendarObject}">
<f:converter converterId="calendarConverter" />
<f:attribute name="pattern" value="#{common.dateFormat}" />
</h:outputText>When the code is rendered in the browser you’ll get a blank response and see the following in the log, “pattern was not specified“. The log statement is generated from out code above where we check for the attribute named “pattern”. This is because of a requirement in the JSF 1.2 specification (JSR-252) that states (Section 9.4.2) that literal (static) text should be stored in the attribute map of the component and non-literal texts should be stored in the value expression map of the component. So to get the pattern from the value expression map we modify the getAsString method as follows:
public String getAsString(FacesContext ctx, UIComponent component, Object value) {
// Get the Calendar to convert
Calendar calendar = (Calendar) value;
String pattern = "";
// Obtain attributes specified along with the converter
Map<String, Object> attributes = component.getAttributes();
// Check if the pattern attribute was specified
if (!attributes.containsKey("pattern")) {
ValueExpression ve = component.getValueExpression("pattern");
if (ve == null) {
System.out.println("pattern was not specified");
return "";
} else {
pattern = (String) ve.getValue(ctx.getELContext());
}
} else {
pattern = attributes.get("pattern");
}
// Create a DateFormatter for the pattern
DateFormat outputFormat = new SimpleDateFormat(pattern);
// Format the calendar
try {
Date date = originalFormat.parse(calendar.getTime());
return outputFormat.format(originalDate));
} catch (ParseException ex) {
ex.printStackTrace();
return "";
}
}The difference is that we now first check to see if there is a literal value specified. If not, we check if there is a value expression, and if there is no value expression either we will fail. If there is a value express we evaluate it and use it as our pattern.
Posted in Java | Comment Now!
Written on October 28, 2008 by Allan Lykke Christensen
Today I stumbled upon the following article about Open Source vs Commercial Software. It’s quite entertaining and shows many of the pros and cons for both open source and commercial software licensing.
http://www.isitedesign.com/insight/08_07/open-source-versus-commercial-web-software.cfm
Enjoy!
Posted in Software engineering | Comment Now!
Written on October 24, 2008 by Allan Lykke Christensen
During the development of my latest pet project I decided to go head-on with many of the latest Java Enterprise APIs. One of these was the Java Persistence API (JPA), which I had already used in a handful of projects before. On previous projects the persistence requirements were very simple. I could use JPA out-of-the-box with TopLink Essentials which is the standard set-up for a JPA project in NetBeans/GlassFish. However, for this new pet project of mine I was in need of storing large binary objects (BLOBs). I was shocked to discover that TopLink Essentials doesn’t support the Fetching configuration for relationships and properties. Instead it will Fetch.EAGER everything in a relationship and property. This made my application crash hard (OutOfMemoryException) when ever I would query for all entities containing the BLOB. So, I set out to replace the persistence provider. First I looked at Hibernate. I used Hibernate before JPA was released and never had much trouble with it. Unfortunately I found that Hibernate also doesn’t support the fetching configuration (in JPA mode). That lead me to OpenJPA which really surprised me. It is well documented, clean, easy to use, and support the fetch configuration. I’ve now replaced the persistence provider on two projects with OpenJPA and the performance has increased significantly. However, here are a few gotchas that you have to look out for:
That’s all for now. I’d love to hear about your experiences with OpenJPA or any other persistence provide you find suitable for your need.
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Written on October 10, 2008 by Allan Lykke Christensen
For the past week I’ve been cycling to and from work. That might not sound like a big deal to you, but it has certainly been a challenge for me. In the past it has been all to easy to jump into the car and head off for work. No more, I’ve decided. The distance to work is very do-able, 5.5 KM each way. It’s better for me and it’s better for the environment. The biggest problem so far has been the uphill route on my way back. Nevertheless, I’ve made great progress already. The first day was absolutely hell! When I got to work I could barely breathe and I had to spend several minutes in the bike shed to compose myself. On the third day I managed to cut off 5 minutes from the ride, and today I was only plagued by fatigue in my joints. I’m looking forward to seeing how I’ll be feeling on Monday and if I can take another week.
Posted in Personal | Comment Now!
