Is there a way to create ruby value objects or hashes from java objects in jruby application ? Thank you.
I am not sure whether this is what you are trying to achieve, but to convert a Java object into a ruby hash, you could do something like this:
require 'java'
java_import 'YourJavaClass'
a = YourJavaClass.new
hash = {}
a.java_class.fields.each{ |var| hash[var.name] = var.value(a) }
p hash
This assumes that the instance variables are accessible (public). If they are not, you may need to make them accessible with something like:
a.java_class.declared_fields.each{ |var| var.accessible = true; hash[var.name] = var.value(a) }
(Note that this time it uses declared_fields)
Names and Beans Convention gives us next opportunity for properties with accessors
def java_to_hash(java_obj)
hash = {}
java_obj.methods.grep(/get_/).each do |accessor|
if accessor.eql? "get_class" then
next
end
#get_user_name => user_name
method_name = accessor[4..-1]
if java_obj.respond_to?(method_name)
hash[method_name.to_sym] = java_obj.send(accessor.to_sym)
end
end
hash
end
Related
For my Java application I am trying to use ScalaCheck to write some property-based unit tests. For that purpose I need generators, but all the tutorials I can find use a constructor with parameters to generate objects.
The object I need to generate does not have constructor parameters, and I cannot add such a constructor since it is from an external library.
I now have the following (JwtClaims is from the package org.jose4j.jwt):
def genClaims: Gen[JwtClaims] = {
val url = arbString
val username = arbString
val claims = new JwtClaims()
claims.setNotBeforeMinutesInThePast(0)
claims.setExpirationTimeMinutesInTheFuture(60)
claims.setSubject(username) // error about Gen[String] not matching type String
claims
}
Any suggestions on how to write my generator? I have zero knowledge of Scala, so please be patient if I've made an 'obvious' mistake :) My expertise is in Java, and testing using ScalaCheck is my first venture into Scala.
You need to be returning a generator of a claims object, not a claims object. The generator is effectively a function that can return a claims object. The normal way I go about this is with a for comprehension (other people prefer flatMap, but I think this reads more clearly).
def genClaims: Gen[JwtClaims] = {
for {
url <- arbitrary[String]
username <- arbitrary[String]
} yield {
val claims = new JwtClaims()
claims.setNotBeforeMinutesInThePast(0)
claims.setExpirationTimeMinutesInTheFuture(60)
claims.setSubject(username)
claims
}
}
steps I do:
I do in code
System.setProperty("myproperty", 1);
and then I set in a shell script the property "myProperty" to 3.
like this:
# setprop "myproperty" 3
and then in the code I try to read the property like this:
System.getProperty("myproperty");
I get the value of 1. which means that the set from the shell didn't actually work.
but when I print all props from shell with
# getprop
I see in the list that myproperty equals 3.
in shorter words: I want to change the value of a property from a script, and I see that this scripts actually changes the property but in the java code I get the old value.
any ideas?
Java code in Android provides System.getProperty and System.setProperty functions in java library but it's important to note that although these java APIs are semantically equal to native version, java version store data in a totally different place. Actually, a hashtable is employed by dalvik VM to store properties. So, java properties are separated, it can't get or set native properties, and neither vice versa.
You can use android.os.SystemProperties class can manipulate native properties, though it's intended for internal usage only. It calls through jni into native property library to get/set properties.
getprop/setprop work on android.os.SystemProperties, not on java.lang.System.
Unfortunately, this class is not available to third party application. Apparently you have rooted your device, so you may still access it.
You can use that snippet to run getProp as shell command and get the value of any property:
private String getSystemProperty(String propertyName) {
String propertyValue = "[UNKNOWN]";
try {
Process getPropProcess = Runtime.getRuntime().exec("getprop " + propertyName);
BufferedReader osRes =
new BufferedReader(new InputStreamReader(getPropProcess.getInputStream()));
propertyValue = osRes.readLine();
osRes.close();
} catch (Exception e) {
// Do nothing - can't get property value
}
return propertyValue;
}
I'm relying on an old Java API that kinda sucks and loves to throw null pointer exceptions when data is missing. I want to create a subclass that has option type accessors but preserves the old accessors until I decide I need to create safe accessors for them. Is there a good way to create a subclass from a copy of the original object? I'd like to achieve something like the following:
SafeIssue extends Issue {
def safeMethod: Option[Value] = { //... }
}
val issue = oldapi.getIssue()
val safeIssue = SafeIssue(issue)
//Preserves issue's methods and data if I need them
val unsafeVal = safeIssue.unsafeMethod
val maybeVal = safeIssue.safeMethod
Why not try an implicit conversion instead? This works better with Java APIs that like to create their own objects. So you would
class SafeIssue(issue: Issue) {
def original = issue
def safeFoo = Option(issue.foo)
// ... You must write any of these you need
}
implicit def make_issues_safe(issue: Issue) = new SafeIssue(issue)
Then you can--as long as you've supplied the method--write things like
val yay = Issue.myStaticFactoryMethodThing.safeFoo.map(x => pleaseNoNull(x))
(You can then decide whether you want to carry SafeIssue or Issue around in your code, and you can always get back the Issue from SafeIssue with the exposed original method (or you could make the issue parameter a val.)
I'm trying to figure a way to do create a class with only the class's name in PHP.
E.g.:
$class = "MyClass";
if(class_exists($class))
$unit = new $class($param1, $param2);
else
$unit = new Unit($param1, $param2);
Is there a way to do this in PHP? If possible, I'd also like to know if this is possible in Java.
Cheers! thanks in advance.
I don't know about PHP (haven't used it in years), but in Java you can do:
MyClass obj = (MyClass) Class.forName("MyClass").newInstance( );
Yep, it should work fine in PHP. I would write that like this in order to avoid duplicating all the parameters to the constructor (if they are the same, of course):
$class = 'MyClass';
if (! class_exists($class)) {
$class = 'Unit';
}
$unit = new $class($param1, $param2);
you can use double $ signs in PHP to make a variable well.. variable.
i.e.
$$class($param1,$param2);
I have not come across such a capability in Java.
Note: you probably don't want to call your class "class" as it is a reserved word ;)
The situation seems to be abnormal, but I was asked to build serializer that will parse an object into string by concatenating results of "get" methods. The values should appear in the same order as their "get" equivalent is declared in source code file.
So, for example, we have
Class testBean1{
public String getValue1(){
return "value1";
}
public String getValue2(){
return "value2";
}
}
The result should be:
"value1 - value2"
An not
"value2 - value1"
It can't be done with Class object according to the documentation. But I wonder if I can find this information in "*.class" file or is it lost? If such data exists, maybe, someone knows a ready to use tool for that purpose? If such information can't be found, please, suggest the most professional way of achieving the goal. I thought about adding some kind of custom annotations to the getters of the class that should be serialized.
If you want that you have to parse the source code, not the byte code.
There are a number of libraries that parse a source file into a node tree, my favorite is the javaparser (hosted at code.google.com), which, in a slightly modified version, is also used by spring roo.
On the usage page you can find some samples. Basically you will want to use a Visitor that listens for MethodDefinitions.
Although reflection does not anymore (as of java 7 I think) give you the methods in the order in which they appear in the source code, the class file appears to still (as of Java 8) contain the methods in the order in which they appear in the source code.
So, you can parse the class file looking for method names and then sort the methods based on the file offset in which each method was found.
If you want to do it in a less hacky way you can use Javassist, which will give you the line number of each declared method, so you can sort methods by line number.
I don't think the information is retained.
JAXB, for example, has #XmlType(propOrder="field1, field2") where you define the order of the fields when they are serialized to xml. You can implemenet something similar
Edit: This works only on concrete classes (the class to inspect has its own .class file). I changed the code below to reflect this. Until diving deeper into the ClassFileAnalyzer library to work with classes directly instead of reading them from a temporary file this limitation exists.
Following approach works for me:
Download and import following libarary ClassFileAnalyzer
Add the following two static methods (Attention! getClussDump() needs a little modification for writing out the class file to a temporary file: I removed my code here because it's very special at this point):
public static String getClassDump(Class<?> c) throws Exception {
String classFileName = c.getSimpleName() + ".class";
URL resource = c.getResource(classFileName);
if (resource == null) {
throw new RuntimeException("Works only for concreate classes!");
}
String absolutePath = ...; // write to temp file and get absolute path
ClassFile classFile = new ClassFile(absolutePath);
classFile.parse();
Info infos = new Info(classFile, absolutePath);
StringBuffer infoBuffer = infos.getInfos();
return infoBuffer.toString();
}
public static <S extends List<Method>> S sortMethodsBySourceOrder(Class<?> c, S methods) throws Exception {
String classDump = getClassDump(c);
int index = classDump.indexOf("constant_pool_count:");
final String dump = classDump.substring(index);
Collections.sort(methods, new Comparator<Method>() {
public int compare(Method o1, Method o2) {
Integer i1 = Integer.valueOf(dump.indexOf(" " + o1.getName() + lineSeparator));
Integer i2 = Integer.valueOf(dump.indexOf(" " + o2.getName() + lineSeparator));
return i1.compareTo(i2);
}});
return methods;
}
Now you can call the sortMethodsBySourceOrder with any List of methods (because sorting arrays is not very comfortable) and you will get the list back sorted.
It works by looking at the class dumps constant pool which in turn can be determined by the library.
Greetz,
GHad
Write your custom annotation to store ordering data, then use Method.getAnnotation(Class annotationClass)