Using Java Compiler API to compile multiple java files - java-compiler-api

Question

Hi I have requirement to create ,compile and load java classes run time. Using FTL i am creating java source files , and able to compile the source if there is no dynamic dependency.
To elaborate with an instance, I have two java source file, one interface and its implementation class. I am able to compile the interface using java compiler api as follows
String classpath=System.getProperty("java.class.path");
String testpath =classpath+";"+rootPath+"/lib/is_wls_client.jar;"+rootPath+"/rtds_wls_proxyclient.jar;.;";
File javaFile = new File(javaFileName+".java");
JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
List<String> optionList = new ArrayList<String>();
optionList.addAll(Arrays.asList("-classpath",testpath));
StandardJavaFileManager sjfm = compiler.getStandardFileManager(null, null, null);
Iterable fileObjects = sjfm.getJavaFileObjects(javaFile);
JavaCompiler.CompilationTask task = compiler.getTask(null, null, null,optionList,null,fileObjects);
task.call();
sjfm.close();
I set class path for static classes which are already in the classpath , but this approach do not work for dynamically created classes? Any custom class loader will do the fix? My final implementation will be in web/app server
Any feedback will be highly appreciated
Satheesh

Answer 1

I was able to solve this issue by compiling all the java files together. Using FTL I generate the java classes, and then compile it using java compiler api and load classes with custom class loader
Java Complier
private void compile(File[] files) throws IOException{
String classpath=System.getProperty("java.class.path");
String rootPath=getServletContext().getRealPath("/");
System.out.println("--> root Path "+rootPath);
String testpath=classpath+";.;xx.jar;yy.jar";
JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
List<String> optionList = new ArrayList<String>();
optionList.addAll(Arrays.asList("-classpath",testpath));
// optionList.addAll(Arrays.asList("-d",rootPath+"/target"));
StandardJavaFileManager sjfm = compiler.getStandardFileManager(null, null, null);
Iterable fileObjects = sjfm.getJavaFileObjects(files);
JavaCompiler.CompilationTask task = compiler.getTask(null, null, null,optionList,null,fileObjects);
task.call();
sjfm.close();
}
Below code snippet shows how to use custom class loader
class CustomClassLoader extends ClassLoader {
public CustomClassLoader(ClassLoader parent) {
super(parent);
}
public Class findClass(String className,String path) {
byte[] classData = null;
try {
FileInputStream f = new FileInputStream(path);
int num = f.available();
classData = new byte[num];
f.read(classData);
} catch (IOException e) {
System.out.println(e);
}
Class x = defineClass(className, classData, 0, classData.length);
return x;
}
}
thanks
Satheesh