How does one decode extension object obtained from HistoryReadResult to HistoryData type ? I read documentation that suggessts simply using the decode() method but the only variant I can find in the source code is that of decode(EncoderContext).
You forgot to mention which stack or SDK you are using, but I can guess that it's the OPC Foundation Java Stack, in which case, you can use EncoderContext.getDefaultInstance(). This will work fine with the standard structure types, such as HistoryData. For server specific types, you may need to use a connection specific EncoderContext.
This question was once asked without a satisfactory answer besides "why would you want to do this" at Reserved words as variable or method names. I'm going to ask it again, and provide context that explains why it is necessary, and even the direction to a proper solution.
I am writing code that builds classes dynamically to match the schema of a database, which I have no control over. For the most part, the code is working cleanly, but in about .1% of the column cases, there are reserved words in Java being used as column names. The following code is being used to create the dynamic field in the class:
evalClass.addField(CtField.make("public " + columnType + " " + columnName + ";", evalClass));
Now, with Java the language, this results in an issue, however in JVM byte code, this should be perfectly legal, so there should be a way to dynamically create this field and access it using byte-code operations. Does anybody have any examples of how this would be done in a way that would support arbitrary strings, including spaces and reserved words? Thanks!
It's not clear which part you are stuck on. Any bytecode manipulation library should let you do this.
For example, using ASM, you just pass your string directly to visitField. There's no hoops to jump through or anything.
Note that even at the bytecode level, there are still a few restrictions on field names. In particular, they can't be more than 65535 bytes long in MUTF8 encoding.
You picked the only way where this doesn’t work—Javassist’s source level API. It should be obvious to you that if you use the identifier to construct source code, the identifier must adhere to the source code rules. Besides, using the already known intended structure to construct source code which has to be parsed again to reconstitute the intention, is the most inefficient way of processing byte code.
You can use the Bytecode level API to overcome these limitations. As a side note, most other byte code processing libraries do not have a source level API at all, so with them you would have used a byte code level API right from the start.
That said, you should rethink your premise. Generated classes whose fields can only be accessed via Reflection or other generated code, do not offer any advantage over, e.g. a HashMap mapping from identifiers to values or arrays intrinsically associating columns with positions.
I couldn't find any documentation about the Scheme and MultiScheme interfaces of Apache Storm. The implementations are here:
https://github.com/apache/storm/tree/master/storm-core/src/jvm/backtype/storm/spout
But I don't understand when I should use Scheme and when I should use MultiScheme. Most example code I found was using implementations of MultiScheme and many also used the mysterious SchemeAsMultiScheme implementation.
Can anyone explain what Scheme, MultiScheme and SchemeAsMultiScheme are actually for? Is there a difference between RawMultiScheme and SchemeAsMultiScheme(new RawScheme())?
There is a decent description on the Storm-Kafka GitHub page (https://github.com/apache/storm/tree/master/external/storm-kafka):
"The default RawMultiScheme just takes the byte[] and returns a tuple with byte[] as is. The name of the outputField is "bytes". There are alternative implementations like SchemeAsMultiScheme and KeyValueSchemeAsMultiScheme which can convert the byte[] to String.
There is also an extension of SchemeAsMultiScheme, MessageMetadataSchemeAsMultiScheme, which has an additional deserialize method that accepts the message byte[] in addition to the Partition and offset associated with the message."
So, given that Java has little to no support to unsigned types, I'm right now writing a small API to handle these (for now, I have UnsignedByte and UnsignedInt). The algorithm is simple: store each of them as their higher representation (byte->short, int->long), extends the Number class and implement some calculation and representation utility methods.
The problem is: it is actually very verbose - and boring - to have to, every time, code things like:
UnsignedByte value = new UnsignedByte(15);
UnsignedByte convert = new UnsignedByte(someIntValue);
I was wondering: is there any way to implement, on Eclipse, something like a "file pre-processor", in a way that it will automatically replace some pre-defined strings with other pre-defined strings before compiling the files?
For example: replace U(x) with new UnsignedByte(x), so it would be possible to use:
UnsignedByte value = U(15);
UnsignedByte convert = U(someIntValue);
Yes, I could create a method called U(...) and use import static, but even then, it would be so much trouble doing it for every class that I would use my unsigned types.
I could write a simple Java program that would replace these expressions in a file, but the problem is: How could I integrate that on Eclipse, in a way that it would call/use it every time a Java file is compiled?
I would recommend using Eclipse Templates for doing this instead. I know its not exactly what you ask for but its very simple and can be achieved out of the box.
When you write sysout in Eclipse and press Ctrl+Space it gives you an option to replace that with System.out.println();
You can find more information in the following link
How to add shortcut keys for java code in eclipse
I can point you at how one project I know of does this, they have a set of Python scripts that generate a whole set of classes (java files) from a template base file. They run the script manually, as opposed to part of the build.
Have a look here for the specific example. In this code they have a class for operating on double, but from this class they want to generate code to operate on float, int, etc all in the same way.
There is, of course, a big debate about whether generated code should be checked in or not to source repository. I leave that issue aside and hope that the above example is good to get you going.
I need to change the signature of a method used all over the codebase.
Specifically, the method void log(String) will take two additional arguments (Class c, String methodName), which need to be provided by the caller, depending on the method where it is called. I can't simply pass null or similar.
To give an idea of the scope, Eclipse found 7000 references to that method, so if I change it the whole project will go down. It will take weeks for me to fix it manually.
As far as I can tell Eclipse's refactoring plugin of Eclipse is not up to the task, but I really want to automate it.
So, how can I get the job done?
Great, I can copy a previous answer of mine and I just need to edit a tiny little bit:
I think what you need to do is use a source code parser like javaparser to do this.
For every java source file, parse it to a CompilationUnit, create a Visitor, probably using ModifierVisitor as base class, and override (at least) visit(MethodCallExpr, arg). Then write the changed CompilationUnit to a new File and do a diff afterwards.
I would advise against changing the original source file, but creating a shadow file tree may me a good idea (e.g. old file: src/main/java/com/mycompany/MyClass.java, new file src/main/refactored/com/mycompany/MyClass.java, that way you can diff the entire directories).
Eclipse is able to do that using Refactor -> Change Method signature and provide default values for the new parameters.
For the class parameter the defaultValue should be this.getClass() but you are right in your comment I don't know how to do for the method name parameter.
IntelliJ IDEA shouldn't have any trouble with this.
I'm not a Java expert, but something like this could work. It's not a perfect solution (it may even be a very bad solution), but it could get you started:
Change the method signature with IntelliJ's refactoring tools, and specify default values for the 2 new parameters:
c: self.getClass()
methodName: Thread.currentThread().getStackTrace()[1].getMethodName()
or better yet, simply specify null as the default values.
I think that there are several steps to dealing with this, as it is not just a technical issue but a 'situation':
Decline to do it in short order due to the risk.
Point out the issues caused by not using standard frameworks but reinventing the wheel (as Paul says).
Insist on using Log4j or equivalent if making the change.
Use Eclipse refactoring in sensible chunks to make the changes and deal with the varying defaults.
I have used Eclipse refactoring on quite large changes for fixing old smelly code - nowadays it is fairly robust.
Maybe I'm being naive, but why can't you just overload the method name?
void thing(paramA) {
thing(paramA, THE_DEFAULT_B, THE_DEFAULT_C)
}
void thing(paramA, paramB, paramC) {
// new method
}
Do you really need to change the calling code and the method signature? What I'm getting at is it looks like the added parameters are meant to give you the calling class and method to add to your log data. If the only requirement is just adding the calling class/method to the log data then Thread.currentThread().getStackTrace() should work. Once you have the StackTraceElement[] you can get the class name and method name for the caller.
If the lines you need replaced fall into a small number of categories, then what you need is Perl:
find -name '*.java' | xargs perl -pi -e 's/log\(([^,)]*?)\)/log(\1, "foo", "bar")/g'
I'm guessing that it wouldn't be too hard to hack together a script which would put the classname (derived from the filename) in as the second argument. Getting the method name in as the third argument is left as an exercise to the reader.
Try refactor using intellij. It has a feature called SSR (Structural Search and Replace). You can refer classes, method names, etc for a context. (seanizer's answer is more promising, I upvoted it)
I agree with Seanizer's answer that you want a tool that can parse Java. That's necessary but not sufficient; what you really want is a tool that can carry out a reliable mass-change.
To do this, you want a tool that can parse Java, can pattern match against the parsed code, install the replacement call, and spit out the answer without destroying the rest of the source code.
Our DMS Software Reengineering Toolkit can do all of this for a variety of languages, including Java. It parses complete java systems of source, builds abstract syntax trees (for the entire set of code).
DMS can apply pattern-directed, source-to-source transformations to achieve the desired change.
To achieve the OP's effect, he would apply the following program transformation:
rule replace_legacy_log(s:STRING): expression -> expression
" log(\s) " -> " log( \s, \class\(\), \method\(\) ) "
What this rule says is, find a call to log which has a single string argument, and replace it with a call to log with two more arguments determined by auxiliary functions class and method.
These functions determine the containing method name and containing class name for the AST node root where the rule finds a match.
The rule is written in "source form", but actually matches against the AST and replaces found ASTs with the modified AST.
To get back the modified source, you ask DMS to simply prettyprint (to make a nice layout) or fidelity print (if you want the layout of the old code preserved). DMS preserves comments, number radixes, etc.\
If the exisitng application has more than one defintion of the "log" function, you'll need to add a qualifier:
... if IsDesiredLog().
where IsDesiredLog uses DMS's symbol table and inheritance information to determine if the specific log refers to the definition of interest.
Il fact your problem is not to use a click'n'play engine that will allow you to replace all occurences of
log("some weird message");
by
log(this.getClass(), new Exception().getStackTrace()[1].getMethodName());
As it has few chances to work on various cases (like static methods, as an example).
I would tend to suggest you to take a look at spoon. This tool allows source code parsing and transformation, allowing you to achieve your operation in a -obviously code based- slow, but controlled operation.
However, you could alos consider transforming your actual method with one exploring stack trace to get information or, even better, internally use log4j and a log formatter that displays the correct information.
I would search and replace log( with log(#class, #methodname,
Then write a little script in any language (even java) to find the class name and the method names and to replace the #class and #method tokens...
Good luck
If the class and method name are required for "where did this log come from?" type data, then another option is to print out a stack trace in your log method. E.g.
public void log(String text)
{
StringWriter sw = new StringWriter();
PrintWriter pw = new PrintWriter(sw, true);
new Throwable.printStackTrace(pw);
pw.flush();
sw.flush();
String stackTraceAsLog = sw.toString();
//do something with text and stackTraceAsLog
}