NoVDL: Write your JSF views in pure Java Ever had to stare down a stack trace like this? ApplicationImpl.newThing:1728 ApplicationImpl.createComponentApplyAnnotations:1894 ApplicationImpl.createComponent:1164 ComponentTagHandlerDelegateImpl.createComponent:524 ComponentTagHandlerDelegateImpl.apply:168 DelegatingMetaTagHandler.apply:120 CompositeFaceletHandler.apply:98 DelegatingMetaTagHandler.applyNextHandler:137 BehaviorsAddingComponentHandlerWrapper.applyNextHandler:53 ComponentTagHandlerDelegateImpl.apply:195 DelegatingMetaTagHandler.apply:120 CompositeFaceletHandler.apply:98 DelegatingMetaTagHandler.applyNextHandler:137 BehaviorsAddingComponentHandlerWrapper.applyNextHandler:53 ComponentTagHandlerDelegateImpl.apply:195 DelegatingMetaTagHandler.apply:120 CompositeFaceletHandler.apply:98 DelegatingMetaTagHandler.applyNextHandler:137 BehaviorsAddingComponentHandlerWrapper.applyNextHandler:53 ComponentTagHandlerDelegateImpl.apply:195 DelegatingMetaTagHandler.apply:120 IfHandler.apply:96 CompositionHandler.apply:166 NamespaceHandler.apply:93 EncodingHandler.apply:86 DefaultFacelet.include:308 DefaultFacelet.include:367 DefaultFaceletContext.includeFacelet:326 UserTagHandler.apply:142 CompositeFaceletHandler.apply:98 InsertHandler.apply:117 CompositeFaceletHandler.apply:98 CompositionHandler.apply:166 NamespaceHandler.apply:93 EncodingHandler.apply:86 DefaultFacelet.include:308 DefaultFacelet.include:367 DefaultFacelet.include:346 DefaultFaceletContext.includeFacelet:199 IncludeHandler.apply:120 IfHandler.apply:96 CompositeFaceletHandler.apply:98 DefineHandler.applyDefinition:107 DecorateHandler.apply:161 DefaultFaceletContext$TemplateManager.apply:395 DefaultFaceletContext.includeDefinition:366 InsertHandler.apply:112 CompositeFaceletHandler.apply:98 DelegatingMetaTagHandler.applyNextHandler:137 BehaviorsAddingComponentHandlerWrapper.applyNextHandler:53 ComponentTagHandlerDelegateImpl.apply:195 DelegatingMetaTagHandler.apply:120 CompositeFaceletHandler.apply:98 ViewHandler.apply:182 NamespaceHandler.apply:93 CompositeFaceletHandler.apply:98 EncodingHandler.apply:86 DefaultFacelet.include:308 DefaultFacelet.include:367 DefaultFacelet.include:346 DefaultFaceletContext.includeFacelet:199 DecorateHandler.apply:145 NamespaceHandler.apply:93 EncodingHandler.apply:86 DefaultFacelet.include:308 DefaultFacelet.include:367 DefaultFacelet.include:346 DefaultFaceletContext.includeFacelet:199 DecorateHandler.apply:145 NamespaceHandler.apply:93 EncodingHandler.apply:86 DefaultFacelet.include:308 DefaultFacelet.include:367 DefaultFacelet.include:346 DefaultFaceletContext.includeFacelet:199 DecorateHandler.apply:145 NamespaceHandler.apply:93 EncodingHandler.apply:86 DefaultFacelet.apply:152 Sorry to do that to you. I know you've seen enough of that already. But don't worry, I'm about to make it up to you by introduction NoVDL. NoVDL is a View Description Language that makes your JSF views more robust by implementing them in Java. By using Java to write your views you automatically gain many features.
Example View
Mapping RoutesThe current implementation maps the view id to its Java implementation by converting the url path to a class name. E.g.
is routed to the class
If you need different functionality, you could rewrite get_view_class_name() and recompile NoVDL. If there is enough demand, I'll make this function configurable. Value ExpressionsNoVDL allows value expressions to be set by using the setter method which ends in x. e.g.
This was chosen partly because the NoVDL components are automatically generated from the JSF API, and partly because EL is discouraged in NoVDL. Ideally, we'd like to be able to implement ValueExpressions using lambda functions. Composite Components with a Static FactoryIt is very easy to make composite components using a static factory method.
This is a good example of why XML is a questionable choice for user interfaces. Is it declarative code or is it procedural? Actually, it's a mixture, and there is not much advantage to declarative languages when you start to mix in procedural (or functional) code. Decorating Views using FunctionsSame idea as above. e.g.
Decorating Views using InheritanceFunction composition is preferred over inheritance. If you like inheritance, all you need to do is make an abstract superclass that defines the sections of your view. e.g.
Mixing Facelets and Java ViewsUse the function
to execute a Facelet from your buildView function. Inside that template, you'll have to reference the components you built using NoVDL. e.g.
Editing Views on the FlyFacelets lets you edit views on the fly without recompiling or restarting the application. You should be able to use HotSwapAgent or JRebel to achieve the same thing with NoVDL. InstallationNoVDL is automatically detected when you add the following dependency. View IDs that cannot be mapped to Java implementations will fall back on the default view decoration language (normally Facelets).
Note: NoVDL requires Java 8. Get the Sourcehttps://github.com/rogerkeays/novdl Spend some time experimenting with NoVDL and let me know how it works for you. |
How to Test if a File is PDF (Java) Here is a simple java function to check if some data represents a PDF file. It is adapted from a C# function posted on Stack Overflow by NinjaCross.
/**
* Test if the data in the given byte array represents a PDF file.
*/
public static boolean is_pdf(byte[] data) {
if (data != null && data.length > 4 &&
data[0] == 0x25 && // %
data[1] == 0x50 && // P
data[2] == 0x44 && // D
data[3] == 0x46 && // F
data[4] == 0x2D) { // -
// version 1.3 file terminator
if (data[5] == 0x31 && data[6] == 0x2E && data[7] == 0x33 &&
data[data.length - 7] == 0x25 && // %
data[data.length - 6] == 0x25 && // %
data[data.length - 5] == 0x45 && // E
data[data.length - 4] == 0x4F && // O
data[data.length - 3] == 0x46 && // F
data[data.length - 2] == 0x20 && // SPACE
data[data.length - 1] == 0x0A) { // EOL
return true;
}
// version 1.3 file terminator
if (data[5] == 0x31 && data[6] == 0x2E && data[7] == 0x34 &&
data[data.length - 6] == 0x25 && // %
data[data.length - 5] == 0x25 && // %
data[data.length - 4] == 0x45 && // E
data[data.length - 3] == 0x4F && // O
data[data.length - 2] == 0x46 && // F
data[data.length - 1] == 0x0A) { // EOL
return true;
}
}
return false;
}
The function takes a byte[] to make it possible to test data in streams and files. To read a file into a byte array you can use java.nio.Files.readAllBytes, e.g:
assertTrue(is_pdf(Files.readAllBytes(Paths.get("output.pdf"));
You'll have to handle the IOExceptions from those methods too. To test streamed output, just render to a ByteArrayOutputStream and call the getBytes() method after the output has rendered. The unit tests for this function are below. Please feel free to contribute test cases, especially ones that fail.
@Test
public void test_valid_pdf_1_3_data_is_pdf() {
assertTrue(is_pdf("%PDF-1.3 CONTENT %%EOF \n".getBytes()));
}
@Test
public void test_valid_pdf_1_4_data_is_pdf() {
assertTrue(is_pdf("%PDF-1.4 CONTENT %%EOF\n".getBytes()));
}
@Test
public void test_invalid_data_is_not_pdf() {
assertFalse(is_pdf("Hello World".getBytes()));
}
|
Access Java Static Methods and Constants from EL Java EL 3.0 provides a way to access static variables and static methods from JSF or JSP, but it's a bit nasty, requiring you to import the packages into your EL Context. I'm lazy and have been using this hack since 2012, so I'm just going to keep doing it for EL 3.0. The hack I'm using makes static methods and constants available via normal managed beans. Note, I'm using Lombok annotations to generate the getters and setters automatically.
@ManagedBean
@ApplicationScoped
@Getter @Setter
public class App {
/* global compile-time constants */
public static final String ROOT_DIR = "/var/local";
public static final String UPLOADS_DIR = "/var/local/uploads";
public static final String IMAGE_DIR = "/var/local/images";
public static final String MANAGER_ROLE = "manager";
/* EL accessors for static constants */
String root_dir = ROOT_DIR;
String uploads_dir = UPLOADS_DIR;
String image_dir = IMAGE_DIR;
String manager_role = MANAGER_ROLE;
/* EL accessors for static methods */
public long ctime() {
return System.currentTimeMillis();
}
}
|
Java With No Design Patterns What have I done? I look down at the code I have just written. It's just one file with one static function and four unit tests. There are no factories, no singletons, no dependency injection, no local or remote interface, no containers, no special annotations, no xml configuration, no inheritence hierarchy, no fancy polymorphism, no abstraction, no black magic, no UML diagrams, no dependencies, no interfaces, no mocks and no side effects. It's just code and tests.
public class ProcessBeacon implements APILayer {
public static boolean processBeacon(Long id, String email, String clientIP) {
// code goes here
}
@Test
public void processing_a_beacon_logs_an_action_in_the_database() {
// test goes here
}
@Test
public void processing_a_beacon_increments_the_open_count() {
// test goes here
}
@Test
public void processing_a_beacon_validates_the_recipients_email_address() {
// test goes here
}
@Test
public void processing_a_beacon_resets_the_recipients_bounce_count() {
// test goes here
}
}
What has gotten into me? How dare I believe I can just write code like that? Without consideration for the greater scheme of object oriented nirvana. Without spending hours philosophising about which class in the universal hierarchy of things my function belongs to. Without considering how to perfectly name it, and how to access and instantiate it. Shame on you. A beginner could have done what you just did. Yes, a beginner could have done it and they would have been way ahead of us developers with over a decade of experience who have lost themselves in the storm of object-oriented design patterns. I've always had this uncomfortable feeling that something was wrong with the way I code. A feeling that I don't know what I am creating. I visualise my applications as complex machine components interacting with each other in fascinating ways. I marvel at the intricacy of how they must be perfectly polished and oiled in order to mesh together. I picture the beauty of how the software agents seamlessly handle the docking of polymorphic components. It's a fantastic image, but it fails to answer my nagging inquiry... what IS it? Is it a machine? Is it a pattern? Is it a virtual life form? Or is it just a jumble of machine code? In a way, my switch to a more basic, functional style of programming has answered my question. Object oriented systems do attempt to create a sort of virtual life form, but this is incongruent with the way computers actually work (and one of the reasons object-oriented design fails so badly at concurrency and multithreading). Computers are Turing Machines which work by streaming long lists of operations which transform data held in the CPU registers. In other words, they simply perform *operations* on *data* and send the results to the user. Now think about how functional programming works. With functional programming you basically chain operations which transform data provided as the input to the function. In other words, you simply perform *operations* on *data* and send the results to the user. Are you starting to see a pattern? Business applications are hugely dominated by operations on data, but unfortunately we've been so sucked into modeling we forget to write code that actually DOES STUFF. Instead we spend most of our time figuring out how to instantiate objects and arguing about it on the Internet. So I've broken all the rules of object oriented design and am implementing all my operations as stateless static methods, one per file with accompanying test cases. I no longer waste my time modeling, I don't have to think about how to access the function (just CALL it!), I don't have to deliberate about where to put new functions and I can spend my somewhat limited brainpower on writing code that actually does something useful. After all... models look great but they don't DO much. |
How To Catch A ClassNotFoundException HTTP request from spammers trying to exploit our commenting system is causing a ClassNotFoundException deep in the JSF / Java code. Specifically, spammers are sending serialized objects in the javax.jsf.ViewState parameter for classes that no longer exist in our system. The resulting exception is this: |
Preserving JSF Request Parameters and REST URLsHave you ever used a URL pattern something like this?
or perhaps this?
Well, as a JSF developer you've probably already realized a little problem. How do you remember the id from request to request? There are a few simple solutions. |
JSF Error Pages That Actually Work Here is an annoying problem using JSF error pages for JSF requests. Everything looks just fine, HttpServletResponse.sendError() sends the error page, but JSF continues processing and starts throwing exceptions after the response is complete. This happens even if you call FacesContext.responseComplete(), and also when the error page is sent at different stages of the JSF lifecycle. It seems like invoking the FacesServlet for sendError() breaks the state of the original FacesContext. When sending an error during view build I get this exception: |
Why Is Maven So Slow? [Solved]![Why Is Maven So Slow? [Solved]](ox/webcore/attachments/22600/maven-logo.png?width=480&height=480){kind=logo} I couldn't figure out why the heck my maven builds where taking so long. I thought Java was supposed to be fast these days and here I am waiting 30 seconds to run a unit test. So I did some digging and eventually found the problem. On Linux, the default JVM is the Server JVM which does all sorts of useful optimisations for long running server process but is absolutely dog slow for building source code (this could also be a reason why the Linux community thinks Java sucks so much). To find out what JVM you are running simply type: $ java -version java version "1.6.0_26" Java(TM) SE Runtime Environment (build 1.6.0_26-b03) Java HotSpot(TM) Server VM (build 20.1-b02, mixed mode) If you see "Server VM" like the example above do me a favor and time your maven compile (mvn clean compile) then switch to the Client VM, time it again and post your results in the comments below. |
How To Create Email From JSF TemplatesHi everybody. In this blog I'm going to share a little trick for creating emails using JSF Facelets templates. The concept is actually independent of JSF and could be used for any servlet-based technology. Right, so the basic idea is to temporarily trick the ServletResponse object into writing all the content to an in-memory buffer, rather than streaming it to the client's browser. We then manually invoke the JSF render phase for the particular view using the special ServletResponse and voila!, the captured output can be put into an email. Let's have a look at some of the code. |
How To Change Maven's Default Resource FolderSometimes it's nice to have your projects resource files alongside the java source files they're related to. By default, Maven forces you to have a separate resource tree so, for example, whenever you need to a add a String for internationalization you have to go digging through your project's folders. The good news is, you can change change maven's default resource folder this with this little bit of XML magic in Maven pom.xml.
<build>
<resources>
<resource>
<directory>src/main/java</directory>
<excludes><exclude>**/*.java</exclude></excludes>
</resource>
</resources>
</build>
Note this overrides the default location, so make sure src/main/resources is empty, or add to the pom.xml like this.
<build>
<resources>
<resource>
<directory>src/main/java</directory>
<excludes><exclude>**/*.java</exclude></excludes>
</resource>
<resource>
<directory>src/main/resources</directory>
</resource>
</resources>
</build>
Don't forget to exclude the java files unless you want to ship your source code! |