I am developing a Spring Boot application using reactive programming. I need to apply Spring Expression Language Related logics inside that application. I will mostly use expression parser related approach as mention in this link.
Since my application is reactive, is it ok to put SpEl related code inside a map like below,
return Mono.just(Person("name", "age:12"))
.map { person ->
// SpEl expression parser related logics here
});
or do I need to execute SpEl related logics in a separate thread using an approach like this
Mono blockingWrapper = Mono.fromCallable(() -> {
return /* SpEl expression parser related logics here */
});
blockingWrapper = blockingWrapper.subscribeOn(Schedulers.boundedElastic());
It is okay to put to the code for actual parsing in the code in map, however suggest to instantiate the Evaluation Context in the Bean which is calling it and pass it using Closure concepts of lambda method.
This is because SpEL does optimization which will be lost if it gets instantiated every time.
Related
I'm using CLR profiling API to profile my .NET Core application.
In the method enter hook I can get the classID and metadata.
Is there any way to invoke another function from that class using metadata?
E.g.: Consider the below example. In the class CommonStats When a method enter/exit hook invoked for the function ProcessRequestInternal, I need to invoke a function GetDefaultValue and save the return value.
public class CommonStats
{
String test =
private void ProcessRequestInternal(String str)
{
test = str;
}
protected override string GetDefaultValue()
{
if(test.StartsWith("/")) {
return "SUCCESS";
}
return "FAILURE";
}
}
In general, it is not recommended (and impossible through the Profiler API) to call managed code from your profiler. The way to do this is performing IL rewriting.
From https://learn.microsoft.com/en-us/dotnet/framework/unmanaged-api/profiling/profiling-overview:
Although this is possible from a design perspective, the profiling API does not support managed components. A CLR profiler must be
completely unmanaged. Attempts to combine managed and unmanaged code
in a CLR profiler may cause access violations, program failure, or
deadlocks. The managed components of the profiler will fire events
back to their unmanaged components, which would subsequently call the
managed components again, resulting in circular references.
The only location where a CLR profiler can call managed code safely is
in the Microsoft intermediate language (MSIL) body of a method. The
recommended practice for modifying the MSIL body is to use the JIT
recompilation methods in the ICorProfilerCallback4 interface.
A good place to start with IL rewriting is http://www.debugthings.com/2015/09/16/rewriting-il-remotely-part1/.
There is a lot of good information found in David's Broman blog, here: https://github.com/dotnet/coreclr/tree/master/Documentation/Profiling/davbr-blog-archive
I am attempting to call out to parallels.js via JSNI. Parallels provides a nice API around web workers, and I wrote some lightweight wrapper code which provides a more convenient interface to workers from GWT than Elemental. However I'm getting an error which has me stumped:
com.google.gwt.core.client.JavaScriptException: (DataCloneError) #io.mywrapper.workers.Parallel::runParallel([Ljava/lang/String;Lcom/google/gwt/core/client/JavaScriptObject;Lcom/google/gwt/core/client/JavaScriptObject;)([Java object: [Ljava.lang.String;#1922352522, JavaScript object(3006), JavaScript object(3008)]): An object could not be cloned.
This comes from, in hosted mode:
at com.google.gwt.dev.shell.BrowserChannelServer.invokeJavascript(BrowserChannelServer.java:249) at com.google.gwt.dev.shell.ModuleSpaceOOPHM.doInvoke(ModuleSpaceOOPHM.java:136) at com.google.gwt.dev.shell.ModuleSpace.invokeNative(ModuleSpace.java:571) at com.google.gwt.dev.shell.ModuleSpace.invokeNativeVoid(ModuleSpace.java:299) at com.google.gwt.dev.shell.JavaScriptHost.invokeNativeVoid(JavaScriptHost.java:107) at io.mywrapper.workers.Parallel.runParallel(Parallel.java)
Here's my code:
Example client call to create a worker:
Workers.spawnWorker(new String[]{"hello"}, new Worker() {
#Override
public String[] work(String[] data) {
return data;
}
#Override
public void done(String[] data) {
int i = data.length;
}
});
The API that provides a general interface:
public class Workers {
public static void spawnWorker(String[] data, Worker worker) {
Parallel.runParallel(data, workFunction(worker), callbackFunction(worker));
}
/**
* Create a reference to the work function.
*/
public static native JavaScriptObject workFunction(Worker worker) /*-{
return worker == null ? null : $entry(function(x) {
worker.#io.mywrapper.workers.Worker::work([Ljava/lang/String;)(x);
});
}-*/;
/**
* Create a reference to the done function.
*/
public static native JavaScriptObject callbackFunction(Worker worker) /*-{
return worker == null ? null : $entry(function(x) {
worker.#io.mywrapper.workers.Worker::done([Ljava/lang/String;)(x);
});
}-*/;
}
Worker:
public interface Worker extends Serializable {
/**
* Called to perform the work.
* #param data
* #return
*/
public String[] work(String[] data);
/**
* Called with the result of the work.
* #param data
*/
public void done(String[] data);
}
And finally the Parallels wrapper:
public class Parallel {
/**
* #param data Data to be passed to the function
* #param work Function to perform the work, given the data
* #param callback Function to be called with result
* #return
*/
public static native void runParallel(String[] data, JavaScriptObject work, JavaScriptObject callback) /*-{
var p = new $wnd.Parallel(data);
p.spawn(work).then(callback);
}-*/;
}
What's causing this?
The JSNI docs say, regarding arrays:
opaque value that can only be passed back into Java code
This is quite terse, but ultimately my arrays are passed back into Java code, so I assume these are OK.
EDIT - ok, bad assumption. The arrays, despite only ostensibly being passed back to Java code, are causing the error (which is strange, because there's very little googleability on DataCloneError.) Changing them to String works; however, String isn't sufficient for my needs here. Looks like objects face the same kinds of issues as arrays do; I saw Thomas' reference to JSArrayUtils in another StackOverflow thread, but I can't figure out how to call it with an array of strings (it wants an array of JavaScriptObjects as input for non-primitive types, which does me no good.) Is there a neat way out of this?
EDIT 2 - Changed to use JSArrayString wherever I was using String[]. New issue; no stacktrace this time, but in the console I get the error: Uncaught ReferenceError: __gwt_makeJavaInvoke is not defined. When I click on the url to the generated script in developer tools, I get this snippet:
self.onmessage = function(e) {self.postMessage((function (){
try {
return __gwt_makeJavaInvoke(3)(null, 65626, jsFunction, this, arguments);
}
catch (e) {
throw e;
}
})(e.data))}
I see that _gwt_makeJavaInvoke is part of the JSNI class; so why would it not be found?
You can find working example of GWT and WebWorkers here: https://github.com/tomekziel/gwtwwlinker/
This is a preliminary work, but using this pattern I was able to pass GWT objects to and from webworker using serialization provided by AutoBeanFactory.
If you never use dev mode it is currently safe to pretend that a Java String[] is a JS array with strings in it. This will break in dev mode since arrays have to be usable in Java and Strings are treated specially, and may break in the future if the compiler optimizes arrays differently.
Cases where this could go wrong in the future:
The semantics of Java arrays and JavaScript arrays are different - Java arrays cannot be resized, and are initialized with specific values based on the component type (the data in the array). Since you are writing Java code, the compiler could conceivable make assumptions based on details about how you create and use that array that could be broken by JS code that doesn't know to never modify the array.
Some arrays of primitive types could be optimized into TypedArrays in JavaScript, more closely following Java semantics in terms of resizing and Java behavior in terms of allocation. This would be a performance boost as well, but could break any use of int[], double[], etc.
Instead, you should copy your data into a JsArrayString, or just use the js array to hold the data rather than going back and forth, depending on your use case. The various JsArray types can be resized and already exist as JavaScript objects that outside JS can understand and work with.
Reply to EDIT 2:
At a guess, the parallel.js script is trying to run your code from another scope such a in the webworker (that's the point of the code, right) where your GWT code isn't present. As such, it can't call the makeJavaInvoke which is the bridge back into dev mode (would be a different failure with compiled JS). According to http://adambom.github.io/parallel.js/ there are specific requirements that a passed callback must meet to be passed in to spawn and perhaps then - your anonymous functions definitely do not meet them, and it may not be possible to maintain java semantics.
Before I get much deeper, check out this answer I did a while ago addressing the basic issues with webworkers and gwt/java: https://stackoverflow.com/a/11376059/860630
As noted there, WebWorkers are effectively new processes, with no shared code or shared state with the original process. The Parallel.js code attempts to paper over this with a little bit of trickery - shared state is only available in the form of the contents passed in to the original Parallel constructor, but you are attempting to pass in instances of 'java' objects and calling methods on them. Those Java instances come with their own state, and potentially can link back to the rest of the Java app by fields in the Worker instance. If I were implementing Worker and doing something that referenced other data than what was passed in, then I would be seeing further bizarre failures.
So the functions you pass in must be completely standalone - they must not refer to external code in any way, since then the function can't be passed off to the webworker, or to several webworkers, each unaware of each other's existence. See https://github.com/adambom/parallel.js/issues/32 for example:
That's not possible since it would
require a shared state across workers
require us to transmit all scope variables (I don't think there's even a possibility to read the available scopes)
The only thing which might be possible would be cache variables, but these can already be defined in the function itself with spawn() and don't make any sense in map (because there's no shared state).
Without being actually familiar with how parallel.js is implemented (all of this answer so far is reading the docs and a quick google search for "parallel.js shared state", plus having experiemented with WebWorkers for a day or so and deciding that my present problem wasn't yet worth the bother), I would guess that then is unrestricted, and you can you pass it whatever you like, but spawn, map, and reduce must be written in such a way that their JS can be passed off to the new JS process and completely stand alone there.
This may be possible from your normal Java code when compiled, provided you have just one implementation of Worker and that impl never uses state other than what is directly passed in. In that case the compiler should rewrite your methods to be static so that they are safe to use in this context. However, that doesn't make for a very useful library, as it seems you are trying to achieve. With that in mind, you could keep your worker code in JSNI to ensure that you follow the parallel.js rules.
Finally, and against the normal GWT rules, avoid $entry for calls you expect to happen in other contexts, since those workers have no access to the normal exception handling and scheduling that $entry enables.
(and finally finally, this is probably still possible if you are very careful at writing Worker implementations and write a Generator that invokes each worker implementation in very specific ways to make sure that com.google.gwt.dev.jjs.impl.MakeCallsStatic and com.google.gwt.dev.jjs.impl.Pruner can correctly act to knock out the this in those instance methods once they've been rewritten as JS functions. I think the cleanest way to do this is to emit the JSNI in the generator itself, call a static method written in real Java, and from that static method call the specific instance method that does the heavy lifting for spawn, etc.)
Assuming that I have a Scala case class that is persisted using the Salat/Casbah/Mongo stack, I want to set up pre-persistence validation logic like I could easily do in Rails using ActiveRecord hooks or in Java using JSR 303 bean validation.
Perhaps there is a better way to think about this in a functional paradigm, but I want to accomplish something like the following:
case class SomeItem(
id: ObjectId = new ObjectId,
someProperty: String) {
#PrePersistence
def validate() = {
//perform some logic
//fail document save in certain conditions
}
}
I am having trouble finding any documentation on how to do something like this in Salat. I do see a #Persist annotation but it seems focused on serializing specific values and not creating hooks.
It seems like one option is to override the save method in the SalatDAO for my case class. Does anyone have an example of this or know of a better, built-in way to handle validation tied to a pre-persistence event?
Thanks!
Salat developer here.
Yes, #Persist is simply for ensuring that fields that aren't in the constructor are serialized - this is particularly useful for manipulating data in MongoDB. One example is where you want to ensure that all the fields are populated with a value so you can sort sensibly, but the value is an Option which may not be present.
Unfortunately, the Java driver doesn't offer lifecycle callbacks like the Ruby driver :(
But what you want should be easy enough to do. Please file an issue at https://github.com/novus/salat/issues and describe how you would like the validation to behave - we can start a discussion and I can try to get something in for you in the 1.9.2 release.
The question was originally asked at http://entityframework.codeplex.com/discussions/399499#post928179 .
Good day! Please tell me if it is wrong place to post this question.
I have a query as follows:
IQueryable<Card> cardsQuery =
dataContext.Cards
.Where(predicate)
.OrderByDescending(kc => kc.SendDate)
.AsQueryable();
Then I try:
Task<Card[]> result = cardsQuery.ToArrayAsync();
And then exception rises:
The source IQueryable doesn't implement IDbAsyncEnumerable<Models.Card>
I use modified version of 'EF 5.x DbCotext generator'.
How to avoid it?
UPDATE
Important remark is that I have method to produce IQuerayble<Card> as follows:
class Repository {
public IQueryable<Card> GetKudosCards(Func<Card, bool> predicate) {
IEnumerable<KudosCard> kudosCards = kudosCardsQuery.Where(predicate);
return kudosCards
.OrderByDescending(kc => kc.SendDate)
.AsQueryable();
}
}
What is the point of calling AsQueryable? If you compose a query with the extension methods starting from an IQueryable source collection (e.g. DbSet, ObjectSet), the query will be IQueryable too.
The purpose of AsQueryable is to wrap an IEnumerable collection with an IQueryable proxy/adapter that uses a Linq provider that is capable of compiling IQueryable queries into a Linq to Object queries. This can be useful in scenarios when you would like to use inmemory data queries.
Why is the AsQueryable call necessary? What if you just simply remove it?
Update
Okey, now it seems I understand your problem. After a quick look on the ODataQueryOptions.ApplyTo I realized that it just extends the underlying expression tree of the query. You can still use it to run the query in the way you want, however you need a little trick to transform the query back to generic.
IQueryable<Card> cardsQuery =
dataContext.Cards
.Where(predicate)
.OrderByDescending(kc => kc.SendDate);
IQueryable odataQuery = queryOptions.ApplyTo(cardsQuery);
// The OData query option applier creates a non generic query, transform it back to generic
cardsQuery = cardsQuery.Provider.CreateQuery<Card>(odataQuery.Expression);
Task<Card[]> result = cardsQuery.ToArrayAsync();
The problem is as follows.
I have a method:
class Repository {
public IQueryable<Card> GetKudosCards(Func<Card, bool> predicate) {
IEnumerable<KudosCard> kudosCards = kudosCardsQuery.Where(predicate);
return kudosCards
.OrderByDescending(kc => kc.SendDate)
.AsQueryable();
}
}
The problem is that kudosCards has type IEnumerable<KudosCard>. That throws exception. If I change predicate type to Expression<Func<Card, bool> predicate then everything works just fine.
I had the same problem when I was using the LinqKit library expression builder, which in the end, was producing AsQueryable(), and very surprisingly it was happening for me from the XUnit Integration Tests call.
I was going wild about why the same problem wasn't happening when calling the same API endpoint via Swagger.
It turned out I had to do an elementary change.
I had to replace:
using System.Data.Entity;
with:
using Microsoft.EntityFrameworkCore;
I had the same problem when I was using the LinqKit library expression builder, which in the end, was producing AsQueryable().
And very surprisingly, it was happening for me from the XUnit Integration Tests call.
I was going wild about why the same problem wasn't happening when calling the same API endpoint via Swagger.
It turned out I had to do an elementary change.
I had to replace the:
using System.Data.Entity;
with:
using Microsoft.EntityFrameworkCore;
In the place where I was calling the LinqKit expression method.
If you want to use the List<T> for Linq query, Avoid chaining it with ToListAsync(). It uses the class IDbAsyncEnumerable that is not available to a normal List<T> object
Does anyone have or know of an example which demonstrates loading data via a GWT RPC call into a ListStore using Sencha GXT 3.0? I know there are numerous examples of using the ModelData and BeanModel interfaces used in the 2.x versions but 3.0 does away with the need to use these interfaces and supposedly allows for POJO objects to be loaded in using classes which implement the ValueProperty interface.
I have seen the RequestFactoryBinding example and the RequestFactory Grid example in the 3.0 Explorer but those appear to demonstrate the use of a custom Data Proxy and a Receiver. I assume from reviewing the code in those examples that these techniques/classes may be required but that is not made apparent anywhere. It's possible that there is more documentation forthcoming but so far I haven't been able to find much of anything beyond that javadocs and the Explorer which lacks some of the source classes used in the example methods.
Links to both examples below.
The RequestFactoryBinding Example:
http://www.sencha.com/examples/#ExamplePlace:requestfactorybinding
RequestFactory Grid example:
http://www.sencha.com/examples/#ExamplePlace:requestfactorygrid
DataProxy and Loader are used mostly to facilitate a) relying on the server for filtering/paging/sorting, or b) reuse between parts of the application for getting access to the same pieces of data. They are not required (as in 2.x) in cases where the client only loads data once, or where manual store management is done.
The various store loading classes (ListStoreBinding, LoadResultListStoreBinding) demonstrate internally how the ListStore can be fed items. This first way allows you to replace the existing items in the store from the onSuccess method in your RPC callback or RequestFactory receiver:
List<MyData> newItems = ...;//response from server
ListStore<MyData> store = ...;//current store to replace/update
store.replaceAll(newItems);
If only loading once, or only appending, not replacing, the other method should be used:
store.addAll(newItems);
Items can be added one by one using store.add, however this will result in an event per item, and should be avoided.
Edit: Also, and this may not totally be clear coming from 2.x, but no superclass/interface is required for data itself. ValueProvider is only used as an external abstraction for how models are manipulated - how values are generically read or set from any kind of model. The PropertyAccess interface allows ValueProvider (and other) instances to be generated by just the property name that the values will be get/set from using bean accessors. ValueProvider types/instances are not required for loading data, merely for the data widgets themselves to extract the data they are displaying, and to make modifications after the user edits the values.
Knowing these pieces, the loader/proxy mechanism will be loading data in the same basic way. The Loader is responsible for being told what settings (paging, filtering, and/or sorting) to use when loading, then triggering the load - different subclasses have different responsibilities, accept different load config types, and return different results. The DataProxy then is the mechanism that actually talks to whatever holds the data, asynchronously if on a server, and informs the loader when the results are available via a callback.
The examples listed in the question both use RequestFactory, but there are several examples as well that use RPC, and a few loading from just JSON or XML. In http://www.sencha.com/examples/#ExamplePlace:paginggrid the main data loading parts are as follows:
// The rpc async instance
final ExampleServiceAsync service = GWT.create(ExampleService.class);
// As in Ext GWT 2, there is a convenience proxy for RPC to just pass the callback
// directly to the RPC call. If you need a custom callback, just be sure to invoke
// `callback.onSuccess` with the final result.
RpcProxy<PagingLoadConfig, PagingLoadResult<Post>> proxy = new RpcProxy<PagingLoadConfig, PagingLoadResult<Post>>() {
#Override
public void load(PagingLoadConfig loadConfig, AsyncCallback<PagingLoadResult<Post>> callback) {
service.getPosts(loadConfig, callback);
}
};
// ...
// The loader itself has a reference to the proxy so that loader.load() results
// in a round trip to the server, as outlined above.
final PagingLoader<PagingLoadConfig, PagingLoadResult<Post>> loader = new PagingLoader<PagingLoadConfig, PagingLoadResult<Post>>(
proxy);
loader.setRemoteSort(true);
// This last piece - instead of 2.x where the loader is a parameter to the store,
// in 3 you directly wire the results of the loader to add the items into the
// store, as discussed in the first half of this answer
loader.addLoadHandler(new LoadResultListStoreBinding<PagingLoadConfig, Post, PagingLoadResult<Post>>(store));
FWIW I spiked a GWTP Dispatch version of a remotely paged and sorted grid. Which is GWT RPC with a command pattern twist.
Assuming you're familiar with grids, you'll require an instance of:
RpcProxy
PagingLoader
LoadResultListStoreBinding
And the methods that need to be invoked:
PagingLoader.setRemoteSort(true)
PagingLoader.addLoadHandler()
Grid.setLoader()
PagingToolBar.bind()