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• Why not .NET-style delegates rather than closures in Java?

  - by h2g2java

  OK, this is going to be my beating a dying horse for the 3rd time. However, this question is different from my earlier two about closures/delegates, which asks about plans for delegates and what are the projected specs and implementation for closures. This question is about - why is the Java community struggling to define 3 different types of closures when we could simply steal the whole concept of delegates lock, stock and barrel from our beloved and friendly neighbour - Microsoft. There are two non-technical conclusions I would be very tempted to jump into: The Java community should hold up its pride, at the cost of needing to go thro convoluted efforts, by not succumbing to borrowing any Microsoft concepts or otherwise vindicate Microsoft's brilliance. Delegates is a Microsoft patented technology. Alright, besides the above two possibilities, Q1. Is there any weakness or inadequacy in msft-styled delegates that the three (or more) forms of closures would be addressing? Q2. I am asking this while shifting between java and c# and it intrigues me that c# delegates does exactly what I needed. Are there features that would be implemented in closures that are not currently available in C# delegates? If so what are they because I cannot see what I need more than what C# delegates has adequately provided me? Q3. I know that one of the concerns about implementing closures/delegates in java is the reduction of orthogonality of the language, where more than one way is exposed to perform a particular task. Is it worth the level convolution and time spent to avoid delegates just to ensure java retains its level of orthogonality? In SQL, we know that it is advisable to break orthogonality by frequently adequately satisfying only the 2nd normal form. Why can't java be subjected to reduction of orthogonality and OO-ness for the sake of simplicity? Q4. The architecture of JVM is technically constrained from implementing .NET-styled delegates. If this reason WERE (subjunctive to emphasize unlikelihood) true, then why can't the three closures proposals be hidden behind a simple delegate keyword or annotation: if we don't like to use @delegate, we could use @method. I cannot see how delegate statement format is more complex than the three closure proposals.

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• JPA/JDO entity to XML XSD generator.

  - by h2g2java

  I am using JDO or JPA on GAE plugin in Eclipse. I am using smartgwt datasource, accepting an xsd. I would like to be educated how to generate an XSD from my jdo/jpa entity, vice versa. Is there a tool to do it? While datanucleas does all its magic enhancing in the Eclipse background, would I be able to somehow operate in a mode that would generate XSDs for me? Can Hibernate operate in an offline mode, to solely help me generate XSDs which I could use in GWT without deploying hibernate with my web-app? Can Hibernate even be capable of generating XSDs from entities, vice versa? Currently, I am about to write a utility to generate an xsd, given an entity class - but I am hoping I don't have to reinvent the wheel if it already exists. I am hoping people here could educate me on any available tools to ease my XSD generation. But btw, I am very wary of anything that uses Maven, because most people (like Spring) who write the Maven scripts and pom don't have the expertise to write it in a way that would spew out messages and verbosity appropriately to make it easy for me to locate model errors.

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• Running your own GAE server

  - by h2g2java

  The question http://stackoverflow.com/questions/2505265/how-difficult-is-it-to-migrate-away-from-google-app-engine triggered me to think about this issue again. I have read of someone running, production-wise, Google app engine development version on their own server. My questions are: Are there any security issues running GAE development on your own server in production mode and exposing it to the www? If so how to mitigate them? Can GAE dev be run on Amazon? Is it possible to port my GAE apps running on Google servers to a GAE running on Amazon, without code changes, but without changing any reference in using other gdata services such as google docs, youtube, gmail, etc. How to configure GAE dev server to use my own hadoop? Or to use Amazon's hadoop?

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• How to ignore/prevent javadoc folder from validation during Eclipse Build?

  - by h2g2java

  In my war is a huge javadoc folder. There is no point in validating it since javadocs are produced by Sun(Oracle) javadoc utility. I have forgotten how I did it the last time. I need to tell Eclipse build not to validate that particular folder. Reasons why I need it: 1. the html produced by Sun javadoc generation utility does not meet the requirement that Eclipse uses - there is a bug report in Eclipse but Eclipse responds that Sun javadoc generator non-compliance is not their fault and that Eclipse intends to stick to their strict compliance. Which results in lots of html errors listed in the problems tab. 2. the javadoc folder is a remote link and high activity on that link is using up my cpu resource, and because it is a link to a remote location, that cpu high activity is sustained for long time until it finishes scanning the whole 35MB javadocs. Thanks - need help.

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• Are there macro facility for Java or C#?

  - by h2g2java

  Macros are useful. Therefore, I occasionally bemoan the absence of macros in Java and C#. Macros allow me to force in-line but allow me the code-manageability of non-macro code. Is there any Java- or C#-based project/product somewhere out there that effectively allow macros or specifying in-line expansion. I am thinking of something like @macro public void hello(int x){ ... } or when I call a method, an @inline annotation preceding the call would effect the called-method to be in-lined. or, should I need to know that I should just trust the compiler to make the best the decision for me that at the best of its analysis it might in-line a call. I hope this question will not lead to debating the pro/cons/usefulness of macros.

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• Best way for launching html/jsp to communicate with GWT module

  - by h2g2java

  I asked this at the GWT forum but I'm impatient for the answer and I seem to get rather good responses here. A html or jsp file is used to launch the xxx.nocache.js, which then decides which browser "permutation" to use. <head> <meta http-equiv="content-type" content="text/html;charset=UTF-8"> <title>xxx</title> <script type="text/javascript" language="javascript" src="xxx.nocache.js"></script> </head> In my case, I am using a jsp. When the JSP is executed, it discovers some conditions. I wish to pass these conditions as values to the GWT module being launched. The "elegant" GWT way to pass these values would be to persist them as request/memcache attributes and then have the GWT module perform RPC to retrieve those values. For example, the JSP discovers that the current user is Whoopy. Shouldn't I simply have the JSP generate javascript to store user = "Whoopy" as a top or namedframe level javascript variable and use JSNI within the module to retrieve the value for user? I have not tried it yet, but I would like to know how anyone might have done it without having to use RPC.

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• What is the equivalent of JPA in .NET?

  - by h2g2java

  I think JPA is nice and convenient ( not to mention standardising, as we used to have every individual programmer doing his/her own thing with a jdbc connection). I would like to use something like jpa with C# to mysql and sqlserver.

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• Java multiple class compositing and boiler plate reduction

  - by h2g2java

  We all know why Java does/should not have multiple inheritance. So this is not questioning about what has already been debated till-cows-come-home. This discusses what we would do when we wish to create a class that has the characteristics of two or more other classes. Probably, most of us would do this to "inherit" from three classes. For simplicity, I left out the constructor.: class Car extends Vehicle { final public Transport transport; final public Machine machine; } So that, Car class directly inherits methods and objects of Vehicle class, but would have to refer to transport and machine explicitly to refer to objects instantiated in Transport and Machine. Car car = new Car(); car.drive(); // from Vehicle car.transport.isAmphibious(); // from Transport car.machine.getCO2Footprint(); // from Machine I thought this was a good idea until when I encounter frameworks that require setter and getter methods. For example, the XML <Car amphibious='false' footPrint='1000' model='Fordstatic999'/> would look for the methods setAmphibious(..), setFootPrint(..) and setModel(..). Therefore, I have to project the methods from Transport and Machine classes class Car extends Vehicle { final public Transport transport; final public Machine machine; public void setAmphibious(boolean b){ this.transport.setAmphibious(b); } public void setFootPrint(String fp){ this.machine.setFootPrint(fp); } } This is OK, if there were just a few characteristics. Right now, I am trying to adapt all of SmartGWT into GWT UIBinder, especially those classes that are not a GWT widget. There are lots of characteristics to project. Wouldn't it be nice if there exists some form of annotation framework that is like this: class Car extends Vehicle @projects {Transport @projects{Machine @projects Guzzler}} { /* No need to explicitly instantiate Transport, Machine or Guzzler */ .... } Where, in case of common names of characteristics exist, the characteristics of Machine would take precedence Guzzler's, and Transport's would have precedence over Machine's, and Vehicle's would have precedence over Transport's. The annotation framework would then instantiate Transport, Machine and Guzzler as hidden members of Car and expand to break-out the protected/public characteristics, in the precedence dictated by the @project annotation sequence, into actual source code or into byte-code. Preferably into byte-code. So that the setFootPrint method is found in both Machine and Guzzler, only that of Machine's would be projected. Questions: Don't you think this is a good idea to have such a framework? Does such a framework already exist? Tell me where/what. Is there an eclipse plugin that does it? Is there a proposal or plan anywhere that you know about such an annotation framework? It would be wonderful too, if the annotation/plugin framework lets me specify that boolean, int, or whatever else needs to be converted from String and does the conversion/parsing for me too. Please advise, somebody. I hope wording of my question was clear enough. Thx. Edited: To avoid OO enthusiasts jumping to conclusion, I have renamed the title of this question.

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• How to get a Class literal from a generically specific Class

  - by h2g2java

  There are methods like these which require Class literals as argument. Collection<EmpInfo> emps = SomeSqlUtil.select( EmpInfo.class, "select * from emps"); or GWT.create(Razmataz.class); The problem presents itself when I need to supply generic specific classes like EmpInfo<String> Razmataz<Integer> The following would be wrong syntax Collection<EmpInfo<String>> emps = SomeSqlUtil.select( EmpInfo<String>.class, "select * from emps"); or GWT.create(Razmataz<Integer>.class); Because you cannot do syntax like Razmataz<Integer>.class So, how would I be able to squeeze a class literal out of EmpInfo<String> Razmataz<Integer> so that I could feed them as arguments to methods requiring Class literals? Further info Okay, I confess that I am asking this primarily for GWT. I have a pair of GWT RPC interface Razmataz. (FYI, GWT RPC interface has to be defined in server-client pairs). I plan to use the same interface pair for communicating whether it be String, Integer, Boolean, etc. GWT.create(Razmataz) for Razmataz<T> complains that, since I did not specify T, GWT compiler treated it as Object. Then GWT compiler would not accept Object class. It needs to be more specific than being an Object. So, it seems there is no way for me to tell GWT.create what T is because a Class literal is a runtime concept while generics is a compile time concept, Right?

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• Assigning an @Annotation enum a value

  - by h2g2java

  I created enum Restrictions{ none, enumeration, fractionDigits, length, maxExclusive, maxInclusive, maxLength, minExclusive, minInclusive, minLength, pattern, totalDigits, whiteSpace; public Restrictions setValue(int value){ this.value = value; return this; } public int value; } So that I could happily do something like this, which is perfectly legal syntax. Restrictions r1 = Restrictions.maxLength.setValue(64); The reason being is, I am using enum to restrict the type of restriction that could be used, and be able to assign a value to that restriction. However, my actual motivation is to use that restriction in an @annotation. @Retention(RetentionPolicy.RUNTIME) @Target({ElementType.TYPE, ElementType.FIELD, ElementType.METHOD}) public @interface Presentable { Restrictions[] restrictions() default Restrictions.none; } So that, I intended to do this: @Presentable(restrictions=Restrictions.maxLength.setValue(64)) public String userName; to which, the compiler croaks The value for annotation enum attribute must be an enum constant expression. Is there a way to accomplish what I wish to accomplish

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• With the advent of HTML 5, is there a point in using COMET anymore?

  - by h2g2java

  I am very tempted to use long wait http or periodic polling by the client to set up pseudo-sockets on the browser side, for an application that would be used publicly. But then on the 2nd thought, I am thinking HTML 5 is here. But on the 3rd thought, what is the percentage of browsers out there that remain non-HTML5 within 12 months, 24 months, 36 months? If there are at least 20% of browsers still incapable of HTML5, then I cannot depend on HTML5 because 20% of users not being able to access an application is a significant amount. What do you think, how would your advice be (to me and to developers in general)? Q1. Is there any point in rigging in COMET into an application anymore? I am thinking of gwt comet - http://code.google.com/p/gwt-comet/. Q2. Should we release a new public application within the next 2 months that is dependent on HTML5 sockets and tell non-HTML5 browser users "sorry, your browser version cannot access this application"? Or should we architect the apps to use communication like GWT RPC? Q3. I am also very distrustful of long wait http request. I have never used it before but I have a horrible feeling about it. I have been using 10 to 20 second client-side polling. Is long wait http request risky (risk of hanging a browser session)? Does long wait request present any additional security risk?

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• non-servlet JSP

  - by h2g2java

  I realise there are EL and near EL frameworks like StringTemplate, JUEL, Velocity, etc. However, I am not asking for list of alternatives to JSTL/EL. I came across a package more than a year ago, someone who wrote a util that emulates the functionality of JSP for non-servlet env, i.e., JSP composition which does not need a "servlet container" to function. I ignored it and now I think it would be helpful to me and I need help to recall what it is. My actual motivation is similar to what StringTemplate, JUEL, Velocity would offer to help me compose SQL blocks, HTML blocks but I am thinking that JSPs are precompiled into bytecode and JSPs are more run-time efficient since run-time parsing is done no more than once. So actually, recommendation for alternatives would be acceptable as long as the templates are precompiled into bytecode. But I still prefer the JSP emulator.

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• Use ini/appconfig file or sql server file to store user config?

  - by h2g2java

  I know that the preference for INI or appconfig XML is their human readability. Let's say user preferences stored for my app are hierarchical and numbers about a thousand items and it would be really confusing for a user to edit an INI to change things anyway. I have always been using a combination of INI with appconfig. I am leaning towards using sql server db file, now. Every time the user changes a preference while using the app, it would be stored into the db file - that's my line of thought. I am also thinking that such a config db file could move around with the app too, just like an INI. Before I do that, any advice 1. If there are any disadvantages against using a db file over INI or appconfig. 2. If a shop uses mysql or oracle, do you think your colleagues would lift up their pro-mysql or pro-oracle eyebrow questioning why you would use sql server technology in a mysql or oracle shop? I mean, I am just using it like an INI file or app.config anyway, right?

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• GWT HTML widget security risks

  - by h2g2java

  In GWT javadoc, we are advised If you only need a simple label (text, but not HTML), then the Label widget is more appropriate, as it disallows the use of HTML, which can lead to potential security issues if not used properly. I would like to be educated/reminded about the security susceptibilities? It would be nice to list the description of the mechanisms of those risks. Are the susceptibilities equally potent on GAE vs Amazon vs my home linux server? Are they equally potent across the browser brands? Thank you.

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• Does GAE/OpenID/OAuth support xmlhttp proxy?

  - by h2g2java

  Currently, my code would construct the GWT form, which user would submit directly to openId (or any authenticaiton service). Such a method works fine. However, what if I had the gwt page server access the OpenID provider, is there a way/strategy for the server to mediate authentication between its client and the auth provider? I wish to know the answers with respect to GAE as the proxy and, regardless if GAE or Tomcat is the intended proxy, answers wrt Google Accounts OpenID OAuth If so, it would be wonderful if someone could describe the installation strategy.

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