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Compile for mixed platform (32, 64) and reference a 32 or 64 bit DLL resolved at runtime

- by Nigel Aston

Using VS2010 under windows 32 or 64 bit. Our C# app calls a 3rd party DLL (managed) that interfaces to an unmanaged DLL. The 3rd party DLL API appears identical in 32 or 64 bit although underneath it links to a 32 or 64 bit unmanaged DLL. We want our C# app to run on either 32 or 64 bit OS, ideally it will auto detect the OS and load the appropriate 32rd party DLL - via a simple factory class which tests the Enviroment. So the neatest solution would be a runtime folder containing: OurApp.exe 3rdParty32.DLL 3rdPartyUnmanaged32.DLL 3rdParty64.DLL 3rdPartyUnmanaged64.DLL However, the interface for the managed 3rdParty 32 and 64 dll is identical so both cannot be referenced within the same VS2010 project: when adding the second the warning triangle is shown and it does not get referenced. Is my only answer to create two extra library DLL projects to reference the 3rdParty 32 and 64 Dlls? So I would end up with this project arrangement: Project 1: Builds OurApp.exe, dynamically creates an object for project2 or project3. Project 2: Builds OurApp32.DLL which references 3rdParty32.dll Project 3: Builds OurApp64.DLL which references 3rdParty64.dll

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Can anyone get app-engine plugin working with Grails on mac os x?

- by tim

I have been trying for 4 days to get app-engine and grails working together on my mac to no avail. I am using latest groovy/grails and appengine sdk versions. Im following the app-engine plugin step by step on the grails site.. http://grails.org/plugin/app-engine Groovy Version: 1.7.1 JVM: 1.5.0_22 Grails 1.3.0.RC1 echo $APPENGINE_HOME reveals /Users/markstim/appengine-java-sdk-1.3.2 I perform the following steps 1. grails create-app myapp 2. cd myapp; grails list-plugins reveals hibernate 1.3.0.RC1 -- Hibernate for Grails tomcat 1.3.0.RC1 -- Apache Tomcat plugin for Grails add the following line to Config.groovy google.appengine.application="myapp" install the plugin for app-engine grails install-plugin app-engine and answer 'jpa' when asked (no errors yet) installed plugins list now looks like app-engine 0.8.9 -- Grails AppEngine plugin gorm-jpa 0.7.1 -- GORM-JPA Plugin then grails run-app and get this error as the server is coming up... [java] WARNING: Nested in org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'pluginManager' defined in ServletContext resource [/WEB-INF/applicationContext.xml]: Invocation of init method failed; nested exception is org.codehaus.groovy.grails.exceptions.NewInstanceCreationException: Could not create a new instance of class [GormJpaGrailsPlugin]!: [java] java.lang.NoClassDefFoundError: org.grails.jpa.JpaPluginSupport then if i navigate to localhost:8080 I get HTTP ERROR: 503 Problem accessing /myapp. Reason: SERVICE_UNAVAILABLE Powered by Jetty://

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Is it possible to have an enum field in a class persisted with OrmLite?

- by htf

Hello. I'm trying to persist the following class with OrmLite: public class Field { @DatabaseField(id = true) public String name; @DatabaseField(canBeNull = false) public FieldType type; public Field() { } } The FieldType is a public enum. The field, corresponding to the type is string in SQLite (is doesn't support enums). When I try to use it, I get the following exception: INFO [main] (SingleConnectionDataSource.java:244) - Established shared JDBC Connection: org.sqlite.Conn@5224ee Exception in thread "main" org.springframework.beans.factory.BeanInitializationException: Initialization of DAO failed; nested exception is java.lang.IllegalArgumentException: Unknown field class class enums.FieldType for field FieldType:name=type,class=class orm.Field at org.springframework.dao.support.DaoSupport.afterPropertiesSet(DaoSupport.java:51) at orm.FieldDAO.getInstance(FieldDAO.java:17) at orm.Field.fromString(Field.java:23) at orm.Field.main(Field.java:38) Caused by: java.lang.IllegalArgumentException: Unknown field class class enums.FieldType for field FieldType:name=type,class=class orm.Field at com.j256.ormlite.field.FieldType.<init>(FieldType.java:54) at com.j256.ormlite.field.FieldType.createFieldType(FieldType.java:381) at com.j256.ormlite.table.DatabaseTableConfig.fromClass(DatabaseTableConfig.java:82) at com.j256.ormlite.dao.BaseJdbcDao.initDao(BaseJdbcDao.java:116) at org.springframework.dao.support.DaoSupport.afterPropertiesSet(DaoSupport.java:48) ... 3 more So how do I tell OrmLite, values on the Java side are from an enum?

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Spring validation has error in XML document from ServletContext resource

- by user1441404

I applied spring validation in my registration page .but the follwing error are shown in my server log of my app engine server. javax.servlet.UnavailableException: org.springframework.beans.factory.xml.XmlBeanDefinitionStoreException: Line 22 in XML document from ServletContext resource [/WEB-INF/spring/appServlet/servlet-context.xml] is invalid; nested exception is org.xml.sax.SAXParseException; lineNumber: 22; columnNumber: 30; cvc-complex-type.2.4.c: The matching wildcard is strict, but no declaration can be found for element 'property'. My code is given below : <?xml version="1.0" encoding="UTF-8"?> <beans:beans xmlns="http://www.springframework.org/schema/mvc" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:beans="http://www.springframework.org/schema/beans" xmlns:context="http://www.springframework.org/schema/context" xsi:schemaLocation="http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc-3.0.xsd http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.0.xsd http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-3.0.xsd http://www.springframework.org/schema/jee http://www.springframework.org/schema/jee/spring-jee-3.0.xsd > <beans:bean name="/register" class="com.my.registration.NewUserRegistration"> <property name="validator"> <bean class="com.my.validation.UserValidator" /> </property> <beans:property name="formView" value="newuser"></beans:property> <beans:property name="successView" value="home"></beans:property> </beans:bean> <beans:bean class="org.springframework.web.servlet.view.InternalResourceViewResolver"> <beans:property name="prefix" value="/WEB-INF/views/" /> <beans:property name="suffix" value=".jsp" /> </beans:bean> </beans:beans>

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Ability to switch Persistence Unit dynamically within the application (JPA)

- by MVK

My application data access layer is built using Spring and EclipseLink and I am currently trying to implement the following feature - Ability to switch the current/active persistence unit dynamically for a user. I tried various options and finally ended up doing the following. In the persistence.xml, declare multiple PUs. Create a class with as many EntityManagerFactory attributes as there are PUs defined. This will act as a factory and return the appropriate EntityManager based on my logic public class MyEntityManagerFactory { @PersistenceUnit(unitName="PU_1") private EntityManagerFactory emf1; @PersistenceUnit(unitName="PU_2") private EntityManagerFactory emf2; public EntityManager getEntityManager(int releaseId) { // Logic goes here to return the appropriate entityManeger } } My spring-beans xml looks like this..  <bean class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean" id="emFactory1"> <property name="persistenceUnitName" value="PU_1" /> </bean> <bean class="org.springframework.orm.jpa.JpaTransactionManager" id="transactionManager1"> <property name="entityManagerFactory" ref="emFactory1"/> </bean> <tx:annotation-driven transaction-manager="transactionManager1"/> The above section is repeated for the second PU (with names like emFactory2, transactionManager2 etc). I am a JPA newbie and I know that this is not the best solution. I appreciate any assistance in implementing this requirement in a better/elegant way! Thanks!

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after assembling jar - No Persistence provider for EntityManager named ....

- by alabalaa

im developing a standalone application and it works fine when starting it from my ide(intellij idea), but after creating an uberjar and start the application from it javax.persistence.spi.PersistenceProvider is thrown saying "No Persistence provider for EntityManager named testPU" here is my persistence.xml which is placed under meta-inf directory: <persistence-unit name="testPU" transaction-type="RESOURCE_LOCAL"> <provider>org.hibernate.ejb.HibernatePersistence</provider> <class>test.model.Configuration</class> <properties> <property name="hibernate.connection.username" value="root"/> <property name="hibernate.connection.driver_class" value="com.mysql.jdbc.Driver"/> <property name="hibernate.connection.password" value="root"/> <property name="hibernate.connection.url" value="jdbc:mysql://localhost:3306/test"/> <property name="hibernate.show_sql" value="true"/> <property name="hibernate.dialect" value="org.hibernate.dialect.MySQLInnoDBDialect"/> <property name="hibernate.c3p0.timeout" value="300"/> <property name="hibernate.hbm2ddl.auto" value="update"/> </properties> </persistence-unit> and here is how im creating the entity manager factory: emf = Persistence.createEntityManagerFactory("testPU"); im using maven and tried the assembly plug-in with the default configuration fot it, i dont have much experience with assembling jars and i dont know if im missing something, so if u have any ideas ill be glad to hear them

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Implementing client callback functionality in WCF

- by PoweredByOrange

The project I'm working on is a client-server application with all services written in WCF and the client in WPF. There are cases where the server needs to push information to the client. I initially though about using WCF Duplex Services, but after doing some research online, I figured a lot of people are avoiding it for many reasons. The next thing I thought about was having the client create a host connection, so that the server could use that to make a service call to the client. The problem however, is that the application is deployed over the internet, so that approach requires configuring the firewall to allow incoming traffic and since most of the users are regular users, that might also require configuring the router to allow port forwarding, which again is a hassle for the user. My third option is that in the client, spawns a background thread which makes a call to the GetNotifications() method on server. This method on the server side then, blocks until an actual notification is created, then the thread is notified (using an AutoResetEvent object maybe?) and the information gets sent to the client. The idea is something like this: Client private void InitializeListener() { Task.Factory.StartNew(() => { while (true) { var notification = server.GetNotifications(); // Display the notification. } }, CancellationToken.None, TaskCreationOptions.LongRunning, TaskScheduler.Default); } Server public NotificationObject GetNotifications() { while (true) { notificationEvent.WaitOne(); return someNotificationObject; } } private void NotificationCreated() { // Inform the client of this event. notificationEvent.Set(); } In this case, NotificationCreated() is a callback method called when the server needs to send information to the client. What do you think about this approach? Is this scalable at all?

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Will this web service accept both raw xml and an object?

- by ChadNC

We have a web service that provides auto insurance quotes and a company that provides an insurance agency management system would like to use the web service for thier client but they want to pass the web service raw xml instead of using the wsdl to create a port, the object the service expects and calling the web method. The web service has performed flawlessly by creating an object like so com.insurance.quotesvc.AgencyQuote service = new com.insurance.quotesvc.AgencyQuote(); com.insurance.quotesvc.QuotePortType port = service.getQuotePortType(); com.insurance.quotesvc.schemas.request.ACORD parameter = null; Then create initialize the request object with the other objects that make up the response. parameter = factory.createACORD(); parameter.setSignonRq(signOn); parameter.setInsurancesSvcRq(svcRq); And send the request to the web service. com.insurance.quotesvc.schemas.response.ACORD result = null; result = port.requestQuote(parameter); By doing that I am able to easily marshall the request and the result into an xml file and do with them as I wish. So if a client was to send the web service via an http post as raw xml inside of a soap envelope. Would the web service be able to handle the xml without any changes being made to the web service or would there need to be changes made to the web service in order for it to handle a request of that type? The web service is a JAX_WS and we currently have both Java and C# clients consuming the web service using the method described above but now there is another client who wants to send raw xml inside of a soap envelope instead of creating the objects. I feel pretty sure that they will be making the call to the web service using vb. I'm sure I'm missing something obvious but it is eluding me at the moment and any help is greatly appreciated.

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Catch a PHP Object Instantiation Error

- by Rob Wilkerson

It's really irking me that PHP considers the failure to instantiate an object a Fatal Error (which can't be caught) for the application as a whole. I have set of classes that aren't strictly necessary for my application to function--they're really a convenience. I have a factory object that attempts to instantiate the class variant that's indicated in a config file. This mechanism is being deployed for message storage and will support multiple store types: DatabaseMessageStore FileMessageStore MemcachedMessageStore etc. A MessageStoreFactory class will read the application's preference from a config file, instantiate and return an instance of the appropriate class. It might be easy enough to slap a conditional around the instantiation to ensure that class_exists(), but MemcachedMessageStore extends PHP's Memcached class. As a result, the class_exists() test will succeed--though instantiation will fail--if the memcached bindings for PHP aren't installed. Is there any other way to test whether a class can be instantiated properly? If it can't, all I need to do is tell the user which features won't be available to them, but let them continue one with the application. Thanks.

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Kohana 3, problem with m2m data adding

- by Marek

Hello I posted this on official forum but with no result. I am getting :Undefined index: enrollment error when trying to save data. My pivot model: class Model_Enrollment extends ORM { protected $_belongs_to = array('page' => array(), 'menugroup' => array()); } Model_Page protected $_has_many = array('templates' => array(), 'menugroups' => array('through' => 'enrollment')); Model_Menugroup protected $_has_many = array('menuitems' => array(), 'pages' => array('through' => 'enrollment')); //Overriden save() method in Model_Menugroup: public function save() { if (empty($this->created)) { $this->created = time(); } parent::save(); $this->reload(); if (! $this->is_global) { if (! empty($this->groupOwnerPagesId) { $page = ORM::factory('page'); foreach($this->groupOwnerPagesId as $id) { $this->add('enrollment', $page->find($id)); } } } } I did: I corrected table names in pivot model by changing them to singular I even now using the same name for pivot table / model = enrollment. The same as in tutorial. Just in case So the pivot table has name 'enrollment' and has 2 columns: page_id , menugroup_id I tried to add pk in pivot table, but it changed nothing I tried to add/remove db relation between pages/menugroups and pivot table (InnoDB) but with no luck I tried save all data in controller, but with the same bad result:( I am still getting the same error: Undefined index: enrollment in ORM line: $columns = array($this-_has_many[$alias]['foreign_key'], $this-_has_many[$alias]['far_key']); Could somebody tell me, what can be else wrong? I have no other ideas:( Kind regards

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What's the proper approach for writing multi-path "story" flows?

- by Basiclife

Hi, I wonder if you can help me. I'm writing a game (2d) which allows players to take multiple routes, some of which branch/merge - perhaps even loop. Each section of the game will decide which section is loaded next. I'm calling each section an IStoryElement - And I'm wondering how best to link these elements up in a way that is easily changed/configured and at the same time, graphable I'm going to have an engine/factory assembly which will load the appropriate StoryElement(s) based on various config options. I initially planned to give each StoryElement a NextElement() As IStoryElement property and a Completed() event. When the vent fires, the engine reads the NextElement property to find the next StoryElement. The downside to this is that if I ever wanted to graph all the routes through the game, I would be unable to - I couldn't determine all possible targets for each StoryElement. I considered a couple of other solutions but they all feel a little clunky - eg Do I need an additional layer of abstraction? ie StoryElementPlayers or similar - Each one would be responsible for stringing together multiple StoryElement perhaps a Series and a ChoicePlayer with each responsible for graphing its own StoryElement - But this will just move the problem up a layer. In short, I need some way of emulating a simple but dynamic workflow (but I'd rather not actually use WWF). Is there a pattern for something this simple? All the ones I've managed to find relate to more advanced control flow (parallel processing, etc.)

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Checking if a function has C-linkage at compile-time

- by scjohnno

Is there any way to check if a given function is declared with C-linkage (that is, with extern "C") at compile-time? I am developing a plugin system. Each plugin can supply factory functions to the plugin-loading code. However, this has to be done via name (and subsequent use of GetProcAddress or dlsym). This requires that the functions be declared with C-linkage so as to prevent name-mangling. It would be nice to be able to throw a compiler error if the referred-to function is declared with C++-linkage (as opposed to finding out at runtime when a function with that name does not exist). Here's a simplified example of what I mean: extern "C" void my_func() { } void my_other_func() { } // Replace this struct with one that actually works template<typename T> struct is_c_linkage { static const bool value = true; }; template<typename T> void assertCLinkage(T *func) { static_assert(is_c_linkage<T>::value, "Supplied function does not have C-linkage"); } int main() { assertCLinkage(my_func); // Should compile assertCLinkage(my_other_func); // Should NOT compile } Thanks.

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Dependency injection in C++

- by Yorgos Pagles

This is also a question that I asked in a comment in one of Miško Hevery's google talks that was dealing with dependency injection but it got buried in the comments. I wonder how can the factory / builder step of wiring the dependencies together can work in C++. I.e. we have a class A that depends on B. The builder will allocate B in the heap, pass a pointer to B in A's constructor while also allocating in the heap and return a pointer to A. Who cleans up afterwards? Is it good to let the builder clean up after it's done? It seems to be the correct method since in the talk it says that the builder should setup objects that are expected to have the same lifetime or at least the dependencies have longer lifetime (I also have a question on that). What I mean in code: class builder { public: builder() : m_ClassA(NULL),m_ClassB(NULL) { } ~builder() { if (m_ClassB) { delete m_ClassB; } if (m_ClassA) { delete m_ClassA; } } ClassA *build() { m_ClassB = new class B; m_ClassA = new class A(m_ClassB); return m_ClassA; } }; Now if there is a dependency that is expected to last longer than the lifetime of the object we are injecting it into (say ClassC is that dependency) I understand that we should change the build method to something like: ClassA *builder::build(ClassC *classC) { m_ClassB = new class B; m_ClassA = new class A(m_ClassB, classC); return m_ClassA; } What is your preferred approach?

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zend_db and join

- by premtemp

Hello, I am trying to understand how to use Zend_DB in my program but I have some problem. The class below (DatabaseService) work when I pass it a simple query. However, if I pass it it query with a join clause my page just hangs and not error is return. I cut and paste the qry in a query browesr and it is valid Any help would be great $SQL = "select name from mytable" $db = new DatabaseService($dbinfo) $db ->fetchall($SQL ) // works ----------------------------------------------------------- $SQL = "select count(*) as cnt from EndPoints join CallID on EndPoints.`CallID` = CallID.CallID where EndPoints.LastRegister >= '2010-04-21 00:00:01' and EndPoints.LastRegister <= '2010-04-21 23:59:59' " $db = new DatabaseService($dbinfo) $db ->fetchall($SQL ) // DOES NO WORK class DatabaseService { function DatabaseService($dbinfo,$dbname="") { try { $dbConfig = array( 'host' => $this->host, 'username' => $this->username, 'password' => $password, 'dbname' => $this->dbname ); $this->db = Zend_Db::factory($this->adapter, $dbConfig); Zend_Db_Table::setDefaultAdapter($this->db); } catch(Zend_Exception $e) { $this->error = $e->getMessage(); Helper::log($this->error); return false; } } public function connnect() { if($this->db !=null) { try { $this->db->getConnection(); return true; } catch (Zend_Exception $e) { $err = "FAILED ::".$e->getMessage()." <br />"; } } return false; } public function fetchall($sql) { $res= $this->db->fetchAll($sql); return $res; } }

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newbie hibernate first level cache confusion

- by Bruce

Hi all I'm just geting to grips with hibernate. Little bit confused. I just wanted to watch the operation of the first level cache, which I understood to batch up queries until the end of the session. But if I create an object, hibernate saves it immediately, so that when I later update it in the same transaction, it has to do an update too: Session session = factory.getCurrentSession(); session.beginTransaction(); Test1 test1 = new Test1(); test1.setName("Test 1"); test1.setValue(10); // Touch it session.save(test1); System.out.println("At checkpoint 1"); test1.setValue(20); session.getTransaction().commit(); I see the sql for the save, then 'At checkpoint 1', then the sql for the update. Do I have something set up wrong or am I misunderstanding hibernate's first level cache? Is there a good document on the first level cache - I didn't find anything in the hibernate docs, but I could easily have missed it.. Thanks!

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Python - Problems using mechanize to log into a difficult website

- by user1781599

× 139886 I am trying to log in to betfair.com by using mechanize. I have tried several ways but it always fail. This is the code I have developed so far, can anyone help me to identify what is wrong with it and how I can improve it to log into my betfair account? Thanks, import cookielib import urllib import urllib2 from BeautifulSoup import BeautifulSoup import mechanize from mechanize import Browser import re bf_username_name = "username" bf_password_name = "password" bf_form_name = "loginForm" bf_username = "xxxxx" bf_password = "yyyyy" urlLogIn = "http://www.betfair.com/" accountUrl = "https://myaccount.betfair.com/account/home?rlhm=0&" # This url I will use to verify if log in has been successful br = mechanize.Browser(factory=mechanize.RobustFactory()) br.addheaders = [("User-Agent","Mozilla/5.0 (Macintosh; Intel Mac OS X 10_5_8) AppleWebKit/537.1 (KHTML, like Gecko) Chrome/21.0.1180.90 Safari/537.1")] br.open(urlLogIn) br.select_form(nr=0) print br.form br.form[bf_username_name] = bf_username br.form[bf_password_name] = bf_password print br.form #just to check username and psw have been recorded correctly responseSubmit = br.submit() response = br.open(accountUrl) text_file = open("LogInResponse.html", "w") text_file.write(responseSubmit.read()) #this file should show the home page with me logged in, but it show home page as if I was not logged it text_file.close() text_file = open("Account.html", "w") text_file.write(response.read()) #this file should show my account page, but it should a pop up with an error text_file.close()

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Custom bean instantiation logic in Spring MVC

- by Michal Bachman

I have a Spring MVC application trying to use a rich domain model, with the following mapping in the Controller class: @RequestMapping(value = "/entity", method = RequestMethod.POST) public String create(@Valid Entity entity, BindingResult result, ModelMap modelMap) { if (entity== null) throw new IllegalArgumentException("An entity is required"); if (result.hasErrors()) { modelMap.addAttribute("entity", entity); return "entity/create"; } entity.persist(); return "redirect:/entity/" + entity.getId(); } Before this method gets executed, Spring uses BeanUtils to instantiate a new Entity and populate its fields. It uses this: ... ReflectionUtils.makeAccessible(ctor); return ctor.newInstance(args); Here's the problem: My entities are Spring managed beans. The reason for this is to inject DAOs on them. Instead of calling new, I use EntityFactory.createEntity(). When they're retrieved from the database, I have an interceptor that overrides the public Object instantiate(String entityName, EntityMode entityMode, Serializable id) method and hooks the factories into that. So the last piece of the puzzle missing here is how to force Spring to use the factory rather than its own BeanUtils reflective approach? Any suggestions for a clean solution? Thanks very much in advance.

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Which way is preferred when doing asynchronous WCF calls?

- by Mikael Svenson

When invoking a WCF service asynchronous there seems to be two ways it can be done. 1. public void One() { WcfClient client = new WcfClient(); client.BegindoSearch("input", ResultOne, null); } private void ResultOne(IAsyncResult ar) { WcfClient client = new WcfClient(); string data = client.EnddoSearch(ar); } 2. public void Two() { WcfClient client = new WcfClient(); client.doSearchCompleted += TwoCompleted; client.doSearchAsync("input"); } void TwoCompleted(object sender, doSearchCompletedEventArgs e) { string data = e.Result; } And with the new Task<T> class we have an easy third way by wrapping the synchronous operation in a task. 3. public void Three() { WcfClient client = new WcfClient(); var task = Task<string>.Factory.StartNew(() => client.doSearch("input")); string data = task.Result; } They all give you the ability to execute other code while you wait for the result, but I think Task<T> gives better control on what you execute before or after the result is retrieved. Are there any advantages or disadvantages to using one over the other? Or scenarios where one way of doing it is more preferable?

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Design issue when having classes implement different interfaces to restrict client actions

- by devoured elysium

Let's say I'm defining a game class that implements two different views: interface IPlayerView { void play(); } interface IDealerView { void deal(); } The view that a game sees when playing the game, and a view that the dealer sees when dealing the game (this is, a player can't make dealer actions and a dealer can't make player actions). The game definition is as following: class Game : IPlayerView, IDealerView { void play() { ... } void deal() { ... } } Now assume I want to make it possible for the players to play the game, but not to deal it. My original idea was that instead of having public Game GetGame() { ... } I'd have something like public IPlayerView GetGame() { ... } But after some tests I realized that if I later try this code, it works: IDealerView dealerView = (IDealerView)GameClass.GetGame(); this works as lets the user act as the dealer. Am I worrying to much? How do you usually deal with this patterns? I could instead make two different classes, maybe a "main" class, the dealer class, that would act as factory of player classes. That way I could control exactly what I would like to pass on the the public. On the other hand, that turns everything a bit more complex than with this original design. Thanks

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Why would one want to use the public constructors on Boolean and similar immutable classes?

- by Robert J. Walker

(For the purposes of this question, let us assume that one is intentionally not using auto(un)boxing, either because one is writing pre-Java 1.5 code, or because one feels that autounboxing makes it too easy to create NullPointerExceptions.) Take Boolean, for example. The documentation for the Boolean(boolean) constructor says: Note: It is rarely appropriate to use this constructor. Unless a new instance is required, the static factory valueOf(boolean) is generally a better choice. It is likely to yield significantly better space and time performance. My question is, why would you ever want to get a new instance in the first place? It seems like things would be simpler if constructors like that were private. For example, if they were, you could write this with no danger (even if myBoolean were null): if (myBoolean == Boolean.TRUE) It'd be safe because all true Booleans would be references to Boolean.TRUE and all false Booleans would be references to Boolean.FALSE. But because the constructors are public, someone may have used them, which means that you have to write this instead: if (Boolean.TRUE.equals(myBoolean)) But where it really gets bad is when you want to check two Booleans for equality. Something like this: if (myBooleanA == myBooleanB) ...becomes this: if ( (myBooleanA == null && myBooleanB == null) || (myBooleanA == null && myBooleanA.equals(myBooleanB)) ) I can't think of any reason to have separate instances of these objects which is more compelling than not having to do the nonsense above. What say you?

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Hashing 11 byte unique ID to 32 bits or less

- by MoJo

I am looking for a way to reduce a 11 byte unique ID to 32 bits or fewer. I am using an Atmel AVR microcontroller that has the ID number burned in at the factory, but because it has to be transmitted very often in a very low power system I want to reduce the length down to 4 bytes or fewer. The ID is guaranteed unique for every microcontroller. It is made up of data from the manufacturing process, basically the coordinates of the silicone on the wafer and the production line that was used. They look like this: 304A34393334-16-11001000 314832383431-0F-09000C00 Obviously the main danger is that by reducing these IDs they become non-unique. Unfortunately I don't have a large enough sample size to test how unique these numbers are. Having said that because there will only be tens of thousands of devices in use and there is secondary information that can be used to help identify them (such as their approximate location, known at the time of communication) collisions might not be too much of an issue if they are few and far between. Is something like MD5 suitable for this? My concern is that the data being hashed is very short, just 11 bytes. Do hash functions work reliably on such short data?

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Implementing a Version check between an Abstract class and it's implementation

- by Michael Stum

I have this abstract class and concrete implementation (they are in different assemblies): public abstract class MyAbstractClass { private static readonly int MyAbstractClassVersion = 1; public abstract int ImplementedVersion { get; } protected MyAbstractClass() { CheckVersion(); } private void CheckVersion() { var message = string.Format( "MyAbstractClass implements Version {0}, concrete is Version {1}", RepositoryVersion, ImplementedVersion); if (!MyAbstractClassVersion.Equals(ImplementedVersion)) throw new InvalidOperationException(message); } } public class ConcreteClass : MyAbstractClass { public ConcreteClass() : base() { // ConcreteClass is guaranteed to have // a constructor that calls the base constructor // I just simplified the example } public override int ImplementedVersion { get { return 2; } } } As you see, I call CheckVersion() from the abstract constructor, to get rid of the "virtual member call in base constructor" message, but I am not sure if that's really the way to do it. Sure, it works, but that doesn't mean it will always work, will it? Also, I wonder if I can get the name of the Concrete Type from the CheckVersion() function? I know that adding new abstract members will force an error anyway (System.TypeLoadException) and I'm not sure if I want this type of strict Versioning, but I'm just curious how it would be done properly given only the abstract class and an implementation (I know I could do it by using interfaces and/or a Factory pattern).

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PropertyPlaceholderConfigurer works from Maven command line, but not from Eclipse?

- by HDave

I have Eclipse configured to use an external maven instance. Nonetheless I have an integration test that runs fine from the command line, but fails from within Eclipse. The error is a class Spring application context bean error: Cannot convert value of type [java.lang.String] to required type The culprit it a bean that sets property values using a PropertyPlaceholderConfigurer.  <bean id="placeholderConfigUuid" class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer"> <property name="systemPropertiesModeName" value="SYSTEM_PROPERTIES_MODE_OVERRIDE" /> <property name="location" value="classpath:database.properties" /> <property name="placeholderPrefix" value="$DS{" /> </bean> I know which bean is failing because it appears in the stack trace and because when I replace the $DS{hibernate.dialect} with a static value it works. I have two questions: 1) Since M2Eclipse is using the same Maven setup as the command line, why does one work and the other fail? 2) How to fix this? I really like the ability to run a single jUnit test from within Eclipse on demand.

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MonoTouch Load image in background

- by user1058951

I am having a problem trying to load an image and display it using System.Threading.Task My Code is as follows Task DownloadTask { get; set; } public string Instrument { get; set; } public PriceChartViewController(string Instrument) { this.Instrument = Instrument; DownloadTask = Task.Factory.StartNew(() => { }); } private void LoadChart(ChartType chartType) { NSData data = new NSData(); DownloadTask = DownloadTask.ContinueWith(prevTask => { try { UIApplication.SharedApplication.NetworkActivityIndicatorVisible = true; NSUrl nsUrl = new NSUrl(chartType.Uri(Instrument)); data = NSData.FromUrl(nsUrl); } finally { UIApplication.SharedApplication.NetworkActivityIndicatorVisible = false; } }); DownloadTask = DownloadTask.ContinueWith(t => { UIImage image = new UIImage(data); chartImageView = new UIImageView(image); chartImageView.ContentScaleFactor = 2f; View.AddSubview(chartImageView); this.Title = chartType.Title; }, CancellationToken.None, TaskContinuationOptions.OnlyOnRanToCompletion, TaskScheduler.FromCurrentSynchronizationContext()); } The second Continue with does not seem to be being called? Initially my code looked like the following without the background processing and it worked perfectly. private void oldLoadChart(ChartType chartType) { UIApplication.SharedApplication.NetworkActivityIndicatorVisible = true; NSUrl nsUrl = new NSUrl(chartType.Uri(Instrument)); NSData data = NSData.FromUrl(nsUrl); UIImage image = new UIImage(data); chartImageView = new UIImageView(image); chartImageView.ContentScaleFactor = 2f; View.AddSubview(chartImageView); this.Title = chartType.Title; UIApplication.SharedApplication.NetworkActivityIndicatorVisible = false; } Does anyone know what I am doing wrong?

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Why use Intent.URI_INTENT_SCHEME

- by hks

while reading Android docs about Widgets I stumbled upon this piece of code whose purpose is to launch a service for retrieving a factory for StackView items. // Set up the intent that starts the StackViewService, which will // provide the views for this collection. Intent intent = new Intent(context, StackWidgetService.class); // Add the app widget ID to the intent extras. intent.putExtra(AppWidgetManager.EXTRA_APPWIDGET_ID, appWidgetIds[i]); intent.setData(Uri.parse(intent.toUri(Intent.URI_INTENT_SCHEME))); // Instantiate the RemoteViews object for the App Widget layout. RemoteViews rv = new RemoteViews(context.getPackageName(), R.layout.widget_layout); // Set up the RemoteViews object to use a RemoteViews adapter. // This adapter connects // to a RemoteViewsService through the specified intent. // This is how you populate the data. rv.setRemoteAdapter(appWidgetIds[i], R.id.stack_view, intent); You can find it here I have a problem understanding why do you need to call intent.setData(Uri.parse(intent.toUri(Intent.URI_INTENT_SCHEME))); I understand that it gives URI a prefix intent://, but is it necessary here?

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