So I'm trying to explore Clojure's internals and I've come across something I'm not quite sure I understand:
From the REPL, I can access RT.var("clojure.core","require") just fine (this is supposed to return the var associated with the "require" symbol in the "clojure.core" namespace):
user=> (clojure.lang.RT/var "clojure.core" "require")
#'clojure.core/require
However, if I try to access it in what I thought was the same way (
user=> (clojure.lang.Var/intern (clojure.lang.Namespace/findOrCreate (clojure.lang.Symbol/intern nil "clojure.main")) (clojure.lang.Symbol/intern nil "require"))
java.lang.IllegalStateException: require already refers to: #'clojure.core/require in namespace: clojure.main (NO_SOURCE_FILE:0)
I get an error that require already refers to something that exists. This is very strange because RT.var is the same as Var.intern, except with the arguments converted to a Namespace and Symbol respectively.
static public Var var(String ns, String name){
return Var.intern(Namespace.findOrCreate(Symbol.intern(null, ns)), Symbol.intern(null, name));
}
I'll do some more digging, but I'm pretty stumped on this one. I've already checked:
1. nil is the same as null
2. I created var2, which returns the namespace argument sent to Var.intern, and var3, which returns the name argument sent to Var.intern. I then pass those two to Var.intern:
user=> (clojure.lang.Var/intern
(clojure.lang.RT/var2 "clojure.main" "require")
(clojure.lang.RT/var3 "clojure.main" "require"))
java.lang.IllegalStateException: require already refers to: #'clojure.core/require in namespace: clojure.main (NO_SOURCE_FILE:0)
Could this be a bug?
This works fine:
(clojure.lang.Var/intern
(clojure.lang.Namespace/findOrCreate
(clojure.lang.Symbol/create "clojure.core"))
(clojure.lang.Symbol/create "require"))
Symbol/intern works also:
(clojure.lang.Var/intern
(clojure.lang.Namespace/findOrCreate
(clojure.lang.Symbol/intern nil "clojure.core"))
(clojure.lang.Symbol/intern nil "require"))
The REPL is just clojure.main, so we can not intern clojure.main/require in a REPL, but clojure.core/require, I think!
Related
I am trying to use Elasticsearch's Java API.
I am trying to create a RestClientBuilder.
Host=createObject("java", "org.apache.http.HttpHost").init(variables.HostName, variables.Port);
Node=createObject("java", "org.elasticsearch.client.Node").init(Host);
RestClient=createObject("java", "org.elasticsearch.client.RestClient").builder(Javacast("org.elasticsearch.client.Node[]", [Node])).build();
I get the error
Cannot convert the value to Java array because type org.elasticsearch.client.Node is unknown.
Also if I just try to use:
RestClient=createObject("java", "org.elasticsearch.client.RestClient").builder(Javacast("org.apache.http.HttpHost[]", [Host]));
I get the following error
Either there are no methods with the specified method name and
argument types or the builder method is overloaded with argument types
that ColdFusion cannot decipher reliably. ColdFusion found 0 methods
that match the provided arguments. If this is a Java object and you
verified that the method exists, use the javacast function to reduce
ambiguity.
This I assume is because ColdFusion doesn't play nicely with varargs
I found a workaround using this method
https://www.bennadel.com/blog/1980-tojava---a-coldfusion-user-defined-function-for-complex-java-casting.htm
I believe there is a bug with Javacast and javaSettings loadPaths not being used.
coldfusion.runtime.Cast$UnknownTypeException: Cannot convert the value
to Java array because type org.elasticsearch.client.Node is unknown.
at coldfusion.runtime.Cast.toJavaArray(Cast.java:1602)
Additionally if I try to perform the actiuons that the UDF takes
local.javaClass = createObject("java", "org.apache.http.HttpHost");
local.HostArrayReflect = createObject("java", "java.lang.reflect.Array");
local.HostArray = local.HostArrayReflect.newInstance(
local.javaClass.GetClass()
, JavaCast( "int", ArrayLen(local.Hosts))
);
for (i=0; i LT ArrayLen(local.Hosts); i=i+1) {
local.HostArrayReflect.Set(local.HostArray, JavaCast("int", i), local.Hosts[i]);
}
I get the error
An exception occurred while instantiating a Java object. The class
must not be an interface or an abstract class. If the class has a
constructor that accepts an argument, you must call the constructor
explicitly using the init(args) method. Error :
org.apache.http.HttpHost
java.lang.NoSuchMethodException: org.apache.http.HttpHost.() at
java.lang.Class.getConstructor0(Class.java:3082) at
java.lang.Class.newInstance(Class.java:412) at
coldfusion.runtime.java.JavaProxy.createObjectWithDefaultConstructor(JavaProxy.java:209)
at coldfusion.runtime.java.JavaProxy.invoke(JavaProxy.java:92)
This happens when I try to run getClass(), but in the UDF there is no issue. A coworker tried to run this on Lucee and it seems to have worked, so I believe there is a bug in CF related to this.
I'm working on a Clojure wrapper for some Java library.
In order to help me debug, I would like to log all calls to specific Java objects.
After searching how I might do this from a raw Java perspective, I discovered the java.lang.reflect.Proxy class and java.lang.reflect.InvocationHandler interfaces.
This led me to find a small snipped posted by R.H. a few years ago :
(defn debug-proxy [obj]
(java.lang.reflect.Proxy/newProxyInstance
(.. obj getClass getClassLoader)
(.. obj getClass getInterfaces)
(proxy [java.lang.reflect.InvocationHandler] []
(invoke [proxy m args]
(apply println m args)
(.invoke m obj args)))))
Small note: I had to change java.lang.reflect.Proxy.newProxyInstance into java.lang.reflect/newProxyInstance to make it work in my REPL, since newProxyInstance is a static method. Corrected version is given so that you may cut & paste it.
With this version, calling methods on the proxy appear work at first :
youpi.core=> (.charAt (debug-proxy "foo") 2)
#object[java.lang.reflect.Method 0x53ce1eb0 public abstract char java.lang.CharSequence.charAt(int)] 2
=> \o
But sadly, calling a method that accepts no argument will not work:
youpi.core=> (.toUpperCase (debug-proxy "foo"))
IllegalArgumentException No matching field found: toUpperCase for class com.sun.proxy.$Proxy1 clojure.lang.Reflector.getInstanceField (Reflector.java:271)
java.lang.IllegalArgumentException: No matching field found: toUpperCase for class com.sun.proxy.$Proxy1
at clojure.lang.Reflector.getInstanceField(Reflector.java:271)
at clojure.lang.Reflector.invokeNoArgInstanceMember(Reflector.java:315)
at youpi.core$eval5981.invokeStatic(form-init3685547971046661105.clj:1)
at youpi.core$eval5981.invoke(form-init3685547971046661105.clj:1)
at clojure.lang.Compiler.eval(Compiler.java:6927)
at clojure.lang.Compiler.eval(Compiler.java:6890)
at clojure.core$eval.invokeStatic(core.clj:3105)
at clojure.core$eval.invoke(core.clj:3101)
at clojure.main$repl$read_eval_print__7408$fn__7411.invoke(main.clj:240)
at clojure.main$repl$read_eval_print__7408.invoke(main.clj:240)
<...>
at java.lang.Thread.run(Thread.java:745)
I tried to update the invoke implementation following advice given in this clojuredocs comment, but it didn't fix.
Here is my (still broken) attempt at implementing the comment's suggestion:
(defn- debug-print-invoke [obj proxy m args]
(apply println m args)
(.invoke m obj args))
(defn debug-proxy [obj]
(java.lang.reflect.Proxy/newProxyInstance
(.. obj getClass getClassLoader)
(.. obj getClass getInterfaces)
(proxy [java.lang.reflect.InvocationHandler] []
(invoke
([proxy m] (debug-print-invoke obj proxy m []))
([proxy m args] (debug-print-invoke obj proxy m args))))))
A good answer would either fix the snippet I've been working with, or suggest an alternative way to achieve the same goal from Clojure.
Executing the following code in Java7
ScriptEngine scriptEngine = new ScriptEngineManager().getEngineByName("js");
Bindings b = scriptEngine.createBindings();
b.put("x", true);
scriptEngine.eval("x&y", b);
I get the error
sun.org.mozilla.javascript.internal.EcmaError: ReferenceError: "b" is not defined. (<Unknown Source>#1) in <Unknown Source> at line number 1
Is there an option to evaluate to null/false for undefined objects, like in JavaScript?
I know that an option will be to do something like "this.x&this.y" instead of "x&y", but I don't have control over that string (user entered).
I browsed a little bit through the Rhino code and it seems that there's no such option.
In the end I will append "this." in front of each variable. This is not by far a desirable solution (I will not even accept my own answer :) ), but for the time being I have no other.
In both the Joy of Clojure and on Alex Miller's Pure Danger Tech blog-post it is recommended that you can print the last stack using something like the following:
(use 'clojure.stacktrace)
(java.util.Date. "foo")
(.printStackTrace *e 5)
But I can't get any of their examples to work, and instead just get
java.lang.NullPointerException: null
Reflector.java:26 clojure.lang.Reflector.invokeInstanceMethod
(Unknown Source) jtown$eval9755.invoke
What's up with this? .printStackTrace seems to be a Java function from the looks of it, so I am not sure why I am bringing clojure.stacktrace into my namespace, in the first place. I read through the clojure.stacktrace API, though, and see an e function, which seems similar too but is not the *e function, which is in core and is supposed to be binding to the last exception, but isn't. Could somebody straighten me out on the best way to check stack-traces?
There are some special vars available when using the REPL and
*e - holds the result of the last exception.
For instance:
core=> (java.util.Date. "foo")
IllegalArgumentException java.util.Date.parse (Date.java:615)
core=> (class *e)
java.lang.IllegalArgumentException
core=> (.printStackTrace *e)
java.lang.IllegalArgumentException
at java.util.Date.parse(Date.java:615)
<not included.....>
You are right, .printStackTrace is the java method that is invoked on the exception class. This is not very straightforward (since its java interop) so clojure.stacktrace namespace has some utilities about working with stack traces
So after
(use 'clojure.stacktrace)
you can use the stacktrace library instead of java interop:
core=> (print-stack-trace *e)
java.lang.IllegalArgumentException: null
at java.util.Date.parse (Date.java:615)
<not included.....>
Obviously in an app, instead of *e, you can do a try - catch and use the related functions as necessary
I use
(.printStackTrace *e *out*)
That seems to work.
Is there a way I can explicitly cast one Java object to another Java class from JRuby?
Sometimes I want to be able to invoke SomeJavaClass#aMethod(MySuperClass) rather than SomeJavaClass#aMethod(MyClass) from JRuby.
From Java, I'd do this:
someJavaObject.aMethod( (MySuperClass) myObj );
but I didn't see a #cast ruby method or anything like that to do the equivalent from JRuby.
Note that the question Casting Java Objects From JRuby lacks an answer for the general case, which is why I'm re-asking the question.
You need to make use of either the #java_send or #java_alias feature available starting with JRuby 1.4 to select the method you wish to call. Example:
class Java::JavaUtil::Arrays
boolean_array_class = [false].to_java(:boolean).java_class
java_alias :boolean_equals, :equals, [boolean_array_class, boolean_array_class]
end
a1 = [false, true]
Java::JavaUtil::Arrays.boolean_equals a1, a1
# => TypeError: for method Arrays.equals expected [class [Z, class [Z]; got: [org.jruby.RubyArray,org.jruby.RubyArray]; error: argument type mismatch
Java::JavaUtil::Arrays.boolean_equals a1.to_java(:boolean), a1.to_java(:boolean)
# => true
a2 = [true, false]
Java::JavaUtil::Arrays.boolean_equals a1.to_java(:boolean), a2.to_java(:boolean)
# => false