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Whew! That’s a lot of explaining to do just because PeopleCode doesn’t resolve all Java methods properly. The parameter types are specified by using their underlying java class, so you definitely want to be sure that you understand the difference between a java class and the object which describes that java class. Now &jImageIOClass is an actual instance, suitable for the reflection work that we’re doing.įinishing things off, in line 1, we created the array of parameter types that we needed for the call to getDeclaredMethod(). &jImageIOClass = GetJavaClass("").forName("") The secret to getting to a instance for a particular class when you don’t have any instances of that class is to do something like this. The PeopleCode reference allows you to call static methods on the class, but if you call getClass() on it, you’ll get an error. But when you have a JavaObject in PeopleCode that you obtained via GetJavaClass (instead of CreateJavaObject), then you actually have a PeopleCode reference to the class and not an instance of.
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You can get the underlying Class object for any Java object by calling the getClass() method (there are examples in the code below). We call the getDeclaredMethod() method of the underlying Class object (this is the actual Java class that defines what a Java class is chicken, meet egg) and pass it the name of the method that we want, along with array of the parameter types (not the parameter values!) that the method expects. We also needed to have the actual Method object. Mainly because we can pass all of the values in at once instead of setting them one by one as CreateJavaArray forces you to do. When we have all of the values that are ever going to be in the array, then using CreateJavaObject with the braces,, at the end of the class name is nicer than using the CreateJavaArray PeopleCode function.
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Getting that parameter array is what line 3 does. The first parameter, &jImageIO, is the same object that we were trying to use before, and the second parameter is an array of parameters that invoke() will pass along to the “real” method. In order to call a method via reflection, we need to have the correct Method classinstance and use it’s invoke method. This is easier to explain working from the bottom up. &jBufImage = & jReadMethod.invoke(&jImageIO, &jReadArgs) &jReadArgs = CreateJavaObject("", CreateJavaObject("java.io.File", &sSourceFileName)) &jReadMethod = &jImageIOClass.getDeclaredMethod("read", &jReadArgTypes) &jReadArgTypes = CreateJavaObject("", &jIOFileClass) This is broken into separate lines for clarity, but as you’ll see in the code, you can combine these where it makes sense. Reflection is how Java lets you determine class metadata (such as what methods it has and what parameters they take) at runtime. In order to call this method from PeopleCode, we’ll need to use reflection. Java can tell these apart by the type of the parameters being sent in, but PeopleCode only uses the number of parameters to differentiate among methods in a Java class with the same name. If you look at the relevant Javadoc, you’ll see that there are indeed multiple versions of the read method. This line of code will trigger the infamous “more than 1 overload matches” PeopleCode error. &jBufImage = &jImageIO.read(CreateJavaObject("java.io.File", &sSourceFileName)) Let’s start by looking at the first line of code that causes problems.
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The example comes from an article that shows how to use the Java Advanced Imaging libraries that are part of the standard Java environment as of Java 1.4. The use case here is to take an image and modify it so that we can stamp some text on it. A more common reason is to avoid needing to distribute the compiled Java code out to each application server (which can be the source of various logistical difficulties).
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Why would you want to avoid writing the Java glue code to simplify things? Well, it’s certainly not to avoid the complexity of Java (as the rest of this post will show). This post will discuss a few tips and techniques for doing it all from the PeopleCode side. One typical workaround when you can’t cross between Java and PeopleCode successfully is to write some additional glue code on the Java side to provide an easier “target” to work with.
ADAPTED BASE64 ENCODING JAVA SERIES
I haven’t written anything on the Java and PeopleCode series (part 1, part 2) recently, so I thought I’d whip something together this evening.Īs previously discussed in the series, there are a few, um, quirks in the bindings between Java and PeopleCode.