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• How to throttle clients in a REST API

  - by Jacques René Mesrine

  I want to limit clients to an upper limit of number of calls to my REST APIs. What should I return to inform clients that they've been throttled ? Amazon S3 is returning HTTP 503 with an error code SlowDown to inform clients. What do you advise ?

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• REST api design to retrieve summary information

  - by Jacques René Mesrine

  I have a scenario in which I have REST API which manages a Resource which we will call Group. A Group is similar in concept to a discussion forum in Google Groups. Now I have two GET access method which I believe needs separate representations. The 1st GET access method retrieves the minimal amount of information about a Group. Given a *group_id* it should return a minimal amount of information like { group_id: "5t7yu8i9io0op", group_name: "Android Developers", is_moderated: true, number_of_users: 34, new_messages: 5, icon: "http://boo.com/pic.png" } The 2nd GET access method retrives summary information which are more statistical in nature like: { group_id: "5t7yu8i9io0op", top_ranking_users: { [ { user: "george", posts: 789, rank: 1 }, { user: "joel", posts: 560, rank: 2 } ...] }, popular_topics: { [ ... ] } } I want to separate these data access methods and I'm currently planning on this design: GET /group/:group_id/ GET /group/:group_id/stat Only the latter will return the statistical information about the group. What do you think about this ?

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• atomic writes to ehcache

  - by Jacques René Mesrine

  Context I am storing a java.util.List inside ehcache. Key(String) --> List<UserDetail> The ordered List contains a Top 10 ranking of my most active users. Problem Concurrent 3rd party clients might be requesting for this list. I have a requirement to be as current as possible with regards to the ranking. Thus if the ranking is changed due the activities of users, the ordered List in the cache must not be left stale for very long. Once I've recalculated a new List, I want to replace the one in cache immediately. Consider a busy scenario whereby multiple concurrent clients are requesting for the ranking; how can I replace the cache item in an fashion such that: Clients can continue to pull a possibly stale snapshot. They should never get a null value. There will only be 1 server thread that writes to the cache.

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• How to generate a unique hash for a URL ?

  - by Jacques René Mesrine

  Given these two images from twitter. http://a3.twimg.com/profile_images/130500759/lowres_profilepic.jpg http://a1.twimg.com/profile_images/58079916/lowres_profilepic.jpg I want to download them to local filesystem & store them in a single directory. How shall I overcome name conflicts ? In the example above, I cannot store them as *lowres_profilepic.jpg*. My design idea is treat the URLs as opaque strings except for the last segment. What algorithms (implemented as f) can I use to hash the prefixes into unique strings. f( "http://a3.twimg.com/profile_images/130500759/" ) = 6tgjsdjfjdhgf f( "http://a1.twimg.com/profile_images/58079916/" ) = iuhd87ysdfhdk That way, I can save the files as:- 6tgjsdjfjdhgf_lowres_profilepic.jpg iuhd87ysdfhdk_lowres_profilepic.jpg I don't want a cryptographic algorithm as it this needs to be a performant operation.

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• For a primary key of an integral type, why is it important to avoid gaps ?

  - by Jacques René Mesrine

  I am generating a surrogate key for a table & due to my hi/lo algorithm, everytime you reboot/restart the machine, gaps may appear. T1: current hi = 10000000 (sequence being dished out .. 1 to 100) Assume that current sequence is 10000050 T2: restart system. T3: System gives out the next_hi as 10000100 (sequence being dished out now ranges from 101 to 200) T4: Next request for a key returns 100001001 From a primary key or indexing internals perspective, why is it important that there be no gaps in the sequences ? I'm asking this for a deeper understanding of mysql specifically. Thanks

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• Update n number of records using JPA with Optimistic locking

  - by Jacques René Mesrine

  I have a table with a column called "count" and I want to run a cron job that will trigger a statement that performs a SQL like this: update summaryTable set count=4; Note that there might be concurrent threads reading & changing the value for "count" when this cron job is triggered. The table has a version column to support Optimistic Locking. What's an efficient way to update the count in JPA ?

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• Windows Aero areas in own C# Applications

  - by René

  I'm wondering about that many new applications, I think most built in WPF, has this really cool Windows Aero Glass interfaces. For example Seesmic or the upcoming Firefox 3.7 Searching in the internet most time it looks like you need a hack to realize this. But seriously: I don't think big software development teams use hacks to roll out their huge used products. So my question is: Windows Aero Glass Areas - How to do? Is it only possible with a hack? Maybe it's just one property, i don't know. I'm WinForms developer so I never tested out WPF. But my Google search didn't look like It is easier with WPF.

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• Dependency on Spring's annotations

  - by Jacques René Mesrine

  I have annotated my classes with @Repository, @Resource, @Component, @Service annotations but these classes must run in 2 environments. The first environment is Spring 2.x based while the other has no spring at all. I'm sure the code will fail without the spring jars & I want to know ideas from you on how I can retain the annotations but still work in both environments

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• C# encrypt whole XML File

  - by René

  I already have a solution for encrypting of several XML nodes or strings. But of course, you can open the local saved XML file and you should see the node tags. For some intelligent people it could be a reference for hidden informations. Is there any way to encrypt and decrypt the whole xml content including all node tags?

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• Problem with .Contains

  - by Rene

  Hello there, I have a little problem which i can't solve. I want to use an SQL-In-Statement in Linq. I've read in this Forum and in other Forums that I have to use the .Contains (with reverse-thinking-notation :-)). As input i have a List of Guids. I first copied them into an array and then did something like that : datatoget = (from p in objectContext.MyDataSet where ArrayToSearch.Contains(p.Subtable.Id.ToString()) select p).ToList(); datatoget is the result in which all records matching the Subtable.Id (which is a Guid) should be stored. Subtable is a Detail-Table from MyData, and the Id is a Guid-Type. I've tried several things (Convert Guid to String, and then using .Contains, etc), but I always get an Exception which says : 'Linq to Entities' doesn't recognize the Method 'Boolean Contains(System.Guid) and is not able to Translate this method into a memory expression. (Something like that, because I'm using the German Version of VS2008) I am using L2E with .NET 3.5 and am programming in C# with VS 2008. I've read several Examples, but it doesn't work. Is it perhaps because of using Guid's instead of strings ? I've also tried to write my own compare-function, but I don't know how to integrate it so that .NET calls my function for comparing.

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• Using HTTP Vary header to decide on a strategy to process a request

  - by Jacques René Mesrine

  I have a specific REST endpoint that creates a topic in a forum; but I want to apply different strategies when processing the request. e.g. If client A makes the call, perform moderation. if client B makes the call, do something else. The easiest would be to add a query param for differentiation: POST /resource?from=xyz Another brilliant idea is to use the Vary HTTP header. POST /resource Vary: xyz Any problems with this approach ?

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• Practices for keeping JavaScript and CSS in sync?

  - by Rene Saarsoo

  I'm working on a large JavaScript-heavy app. Several pieces of JavaScript have some related CSS rules. Our current practice is for each JavaScript file to have an optional related CSS file, like so: MyComponent.js // Adds CSS class "my-comp" to div MyComponent.css // Defines .my-comp { color: green } This way I know that all CSS related to MyComponent.js will be in MyComponent.css. But the thing is, I all too often have very little CSS in those files. And all too often I feel that it's too much effort to create a whole file to just contain few lines of CSS - it would be easier to just hardcode the styles inside JavaScript. But this would be the path to the dark side... Lately I've been thinking of embedding the CSS directly inside JavaScript - so it could still be extracted in the build process and merged into one large CSS file. This way I wouldn't have to create a new file for every little CSS-piece. Additionally when I move/rename/delete the JavaScript file I don't have to additionally move/rename/delete the CSS file. But how to embed CSS inside JavaScript? In most other languages I would just use string, but JavaScript has some issues with multiline strings. The following looks IMHO quite ugly: Page.addCSS("\ .my-comp > p {\ font-weight: bold;\ color: green;\ }\ "); What other practices have you for keeping your JavaScript and CSS in sync?

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• NHibernate mapping one table on two classes with where selection

  - by Rene Schulte

  We would like to map a single table on two classes with NHibernate. The mapping has to be dynamically depending on the value of a column. Here's a simple example to make it a bit clearer: We have a table called Person with the columns id, Name and Sex. The data from this table should be mapped either on the class Male or on the class Female depending on the value of the column Sex. In Pseudocode: create instance of Male with data from table Person where Person.Sex = 'm'; create instance of Female with data from table Person where Person.Sex = 'f'; The benefit is we have strongly typed domain models and can later avoid switch statements. Is this possible with NHibernate or do we have to map the Person table into a flat Person class first? Then afterwards we would have to use a custom factory method that takes a flat Person instance and returns a Female or Male instance. Would be good if NHibernate (or another library) can handle this.

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• What frameworks to use to bootstrap my first production scala project ?

  - by Jacques René Mesrine

  I am making my first foray into scala for a production app. The app is currently packaged as a war file. My plan is to create a jar file of the scala compiled artifacts and add that into the lib folder for the war file. My enhancement is a mysql-backed app exposed via Jersey & will be integrated with a 3rd party site via HttpClient invocations. I know how to do this via plain java. But when doing it in scala, there are several decision points that I am pussyfooting on. scala 2.7.7 or 2.8 RC ? JDBC via querulous Is this API ready for production ? sbt vs maven. I am comfortable with maven. Is there a scala idiomatic wrapper for HttpClient (or should I use it just like in java) ? I'd love to hear your comments and experiences on starting out with scala. Thanks

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• How best to store Subversion version information in EAR's?

  - by Rene

  When receiving a bug report or an it-doesnt-work message one of my initials questions is always what version? With a different builds being at many stages of testing, planning and deploying this is often a non-trivial question. I the case of releasing Java JAR (ear, jar, rar, war) files I would like to be able to look in/at the JAR and switch to the same branch, version or tag that was the source of the released JAR. How can I best adjust the ant build process so that the version information in the svn checkout remains in the created build? I was thinking along the lines of: adding a VERSION file, but with what content? storing information in the META-INF file, but under what property with which content? copying sources into the result archive added svn:properties to all sources with keywords in places the compiler leaves them be I ended up using the svnversion approach (the accepted anwser), because it scans the entire subtree as opposed to svn info which just looks at the current file / directory. For this I defined the SVN task in the ant file to make it more portable. <taskdef name="svn" classname="org.tigris.subversion.svnant.SvnTask"> <classpath> <pathelement location="${dir.lib}/ant/svnant.jar"/> <pathelement location="${dir.lib}/ant/svnClientAdapter.jar"/> <pathelement location="${dir.lib}/ant/svnkit.jar"/> <pathelement location="${dir.lib}/ant/svnjavahl.jar"/> </classpath> </taskdef> Not all builds result in webservices. The ear file before deployment must remain the same name because of updating in the application server. Making the file executable is still an option, but until then I just include a version information file. <target name="version"> <svn><wcVersion path="${dir.source}"/></svn> <echo file="${dir.build}/VERSION">${revision.range}</echo> </target> Refs: svnrevision: http://svnbook.red-bean.com/en/1.1/re57.html svn info http://svnbook.red-bean.com/en/1.1/re13.html subclipse svn task: http://subclipse.tigris.org/svnant/svn.html svn client: http://svnkit.com/

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• Better way to call superclass method in ExtJS

  - by Rene Saarsoo

  All the ExtJS documentation and examples I have read suggest calling superclass methods like this: MyApp.MyPanel = Ext.extend(Ext.Panel, { initComponent: function() { // do something MyPanel specific here... MyApp.MyPanel.superclass.initComponent.call(this); } }); I have been using this pattern for quite some time and the main problem is, that when you rename your class then you also have to change all the calls to superclass methods. That's quite inconvenient, often I will forget and then I have to track down strange errors. But reading the source of Ext.extend() I discovered, that instead I could use the superclass() or super() methods that Ext.extend() adds to the prototype: MyApp.MyPanel = Ext.extend(Ext.Panel, { initComponent: function() { // do something MyPanel specific here... this.superclass().initComponent.call(this); } }); In this code renaming MyPanel to something else is simple - I just have to change the one line. But I have doubts... I haven't seen this documented anywhere and the old wisdom says, I shouldn't rely on undocumented behaviour. I didn't found a single use of these superclass() and supr() methods in ExtJS source code. Why create them when you aren't going to use them? Maybe these methods were used in some older version of ExtJS but are deprecated now? But it seems such a useful feature, why would you deprecate it? So, should I use these methods or not?

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• C# SQL Data Adapter System.Data.StrongTypingException

  - by René

  I get my data from SQL to Dataset with Fill. It's just one table with two columns (CategoryId (int) and CategoryName (varchar)). When I look at my dataset after fill method, CategoryId Columns seems to be correct. But in the CategoryName I have a *System.Data.StrongTypingExceptio*n. What could that mean? Any Ideas?

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• How to differentiate between time to live and time to idle in ehcache

  - by Jacques René Mesrine

  The docs on ehache says: timeToIdleSeconds: Sets the time to idle for an element before it expires. i.e. The maximum amount of time between accesses before an element expires timeToLiveSeconds: Sets the time to live for an element before it expires. i.e. The maximum time between creation time and when an element expires. I understand timeToIdleSeconds But does it means that after the creation & first access of a cache item, the timeToLiveSeconds is not applicable anymore ?

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• How do I write JPA QL statements that hints to the runtime to use the DEFAULT value ?

  - by Jacques René Mesrine

  I have a table like so: mysql> show create table foo; CREATE TABLE foo ( network bigint NOT NULL, activeDate datetime NULL default '0000-00-00 00:00:00', ... ) In the domain object, FooVO the activeDate member is annotated as Temporal. If I don't set activeDate to a valid Date instance, a new record is inserted with NULLs. I want the default value to take effect if I don't set the activeDate member. Thanks.

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• scala REPL is slow on vista

  - by Jacques René Mesrine

  I installed scala-2.8.0.RC3 by extracting the tgz file into my cygwin (vista) home directory. I made sure to set $PATH to scala-2.8.0.RC3/bin. I start the REPL by typing: $ scala Welcome to Scala version 2.8.0.RC3 (Java HotSpot(TM) Client VM, Java 1.6.0_20). Type in expressions to have them evaluated. Type :help for more information. scala> Now when I tried to enter an expression scala> 1 + 'a' the cursor hangs there without any response. Granted that I have chrome open with a million tabs and VLC playing in the background, but CPU utilization was 12% and virtual memory was about 75% utilized. What's going on ? Do I have to set the CLASSPATH or perform other steps.

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• How to turn off autosignin of registered transports in Openfire ?

  - by Jacques René Mesrine

  This is regarding the gateway XEP 0100 support in Openfire. I have noticed that for some transports, they are auto-signed in once a connection to openfire succeeds (via the xmpp user). This applies specifically to QQ. How does one turn off this auto-signin feature ? Basically from a client perspective, I want to be able to signin selectively. So when I create an XMPPConnection to openfire, all transports should remain signed off until I send directed Presences to transports.

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• How to ensure that no non-ascii unicode characters are entered ?

  - by Jacques René Mesrine

  Given a java.lang.String instance, I want to verify that it doesn't contain any unicode characters that are not ASCII alphanumerics. e.g. The string should be limited to [A-Za-z0-9.]. What I'm doing now is something very inefficient: import org.apache.commons.lang.CharUtils; String s = ...; char[] ch = s.toCharArray(); for( int i=0; i<ch.length; i++) { if( ! CharUtils.isAsciiAlphanumeric( ch[ i ] ) throw new InvalidInput( ch[i] + " is invalid" ); } Is there a better way to solve this ?

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• What is the fastest way to learn JPA ?

  - by Jacques René Mesrine

  I'm looking for the best resources (books, frameworks, tutorials) that will help me get up to speed with JPA. I've been happily using iBatis/JDBC for my persistence needs, so I need resources that will hopefully provide comparable functions on how to do things. e.g. how to I set the isolation level for each transaction ? I know there might be 10 books on the topic, so hopefully, your recommendation could narrow down to the best 2 books. Should I start with OpenJPA or are there other opensource JPA frameworks to use ? P.S. Do suggest if I should learn JPA2 or JPA1 ? My goal ultimately is to be able to write a Google App Engine app (which uses JPA1). Thanks Jacque

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• Partitioning requests in code among several servers

  - by Jacques René Mesrine

  I have several forum servers (what they are is irrelevant) which stores posts from users and I want to be able to partition requests among these servers. I'm currently leaning towards partitioning them by geographic location. To improve the locality of data, users will be separated into regions e.g. North America, South America and so on. Is there any design pattern on how to implement the function that maps the partioning property to the server, so that this piece of code has high availability and would not become a single point of failure ? f( Region ) -> Server IP

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• How to maintain a pool of names ?

  - by Jacques René Mesrine

  I need to maintain a list of userids (proxy accounts) which will be dished out to multithreaded clients. Basically the clients will use the userids to perform actions; but for this question, it is not important what these actions are. When a client gets hold of a userid, it is not available to other clients until the action is completed. I'm trying to think of a concurrent data structure to maintain this pool of userids. Any ideas ? Would a ConcurrentQueue do the job ? Clients will dequeue a userid, and add back the userid when they are finished with it.

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