java

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import java.io.*; /* A CompilingClassLoader compiles your Java source on-the-fly. It checks for nonexistent .class files, or .class files that are older than their corresponding source code. */ public class CompilingClassLoader extends ClassLoader { // Given a filename, read the entirety of that file from disk // and return it as a byte array. private byte[] getBytes( String filename ) throws IOException { // Find out the length of the file File file = new File( filename ); long len = file.length(); // Create an array that's just the right size for the file's // contents byte raw[] = new byte[(int)len]; // Open the file FileInputStream fin = new FileInputStream( file ); // Read all of it into the array; if we don't get all, // then it's an error. int r = fin.read( raw ); if (r != len) throw new IOException( "Can't read all, " r " != " len ); // Don't forget to close the file! fin.close(); // And finally return the file contents as an array return raw; } // Spawn a process to compile the java source code file // specified in the 'javaFile' parameter. Return a true if // the compilation worked, false otherwise. private boolean compile( String javaFile ) throws IOException { // Let the user know what's going on System.out.println( "CCL: Compiling " javaFile "..." ); // Start up the compiler Process p = Runtime.getRuntime().exec( "javac " javaFile ); // Wait for it to finish running try { p.waitFor(); } catch( InterruptedException ie ) { System.out.println( ie ); } // Check the return code, in case of a compilation error int ret = p.exitValue(); // Tell whether the compilation worked return ret==0; } // The heart of the ClassLoader -- automatically compile // source as necessary when looking for class files public Class loadClass( String name, boolean resolve ) throws ClassNotFoundException { // Our goal is to get a Class object Class clas = null; // First, see if we've already dealt with this one clas = findLoadedClass( name ); //System.out.println( "findLoadedClass: " clas ); // Create a pathname from the class name // E.g. java.lang.Object => java/lang/Object String fileStub = name.replace( '.', '/' ); // Build objects pointing to the source code (.java) and object // code (.class) String javaFilename = fileStub ".java"; String classFilename = fileStub ".class"; [1] [2] File javaFile = new File( javaFilename ); File classFile = new File( classFilename ); //System.out.println( "j " javaFile.lastModified() " c " // classFile.lastModified() ); // First, see if we want to try compiling. We do if (a) there // is source code, and either (b0) there is no object code, // or (b1) there is object code, but it's older than the source if (javaFile.exists() && (!classFile.exists() || javaFile.lastModified() > classFile.lastModified())) { try { // Try to compile it. If this doesn't work, then // we must declare failure. (It's not good enough to use // and already-existing, but out-of-date, classfile) if (!compile( javaFilename ) || !classFile.exists()) { throw new ClassNotFoundException( "Compile failed: " javaFilename ); } } catch( IOException ie ) { // Another place where we might come to if we fail // to compile throw new ClassNotFoundException( ie.toString() ); } } // Let's try to load up the raw bytes, assuming they were // properly compiled, or didn't need to be compiled try { // read the bytes byte raw[] = getBytes( classFilename ); // try to turn them into a class clas = defineClass( name, raw, 0, raw.length ); } catch( IOException ie ) { // This is not a failure! If we reach here, it might // mean that we are dealing with a class in a library, // such as java.lang.Object } //System.out.println( "defineClass: " clas ); // Maybe the class is in a library -- try loading // the normal way if (clas==null) { clas = findSystemClass( name ); } //System.out.println( "findSystemClass: " clas ); // Resolve the class, if any, but only if the "resolve" // flag is set to true if (resolve && clas != null) resolveClass( clas ); // If we still don't have a class, it's an error if (clas == null) throw new ClassNotFoundException( name ); // Otherwise, return the class return clas; } } 上一页 [1] [2]