add a prepare phase on compiling

src/de/inetsoftware/jwebassembly/JWebAssembly.java

@@ -157,6 +157,10 @@ public class JWebAssembly {
      *             if any conversion error occurs
      */
     private void compile( ModuleWriter writer ) throws IOException, WasmException {
+        for( URL url : classFiles ) {
+            ClassFile classFile = new ClassFile( new BufferedInputStream( url.openStream() ) );
+            writer.prepare( classFile );
+        }
         for( URL url : classFiles ) {
             ClassFile classFile = new ClassFile( new BufferedInputStream( url.openStream() ) );
             writer.write( classFile );

src/de/inetsoftware/jwebassembly/module/ModuleWriter.java

@@ -20,6 +20,7 @@ import java.io.IOException;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Map;
+import java.util.function.Consumer;
 
 import javax.annotation.Nonnegative;
 import javax.annotation.Nonnull;
@@ -30,6 +31,7 @@ import de.inetsoftware.classparser.ClassFile;
 import de.inetsoftware.classparser.Code;
 import de.inetsoftware.classparser.CodeInputStream;
 import de.inetsoftware.classparser.ConstantPool;
+import de.inetsoftware.classparser.ConstantRef;
 import de.inetsoftware.classparser.LineNumberTable;
 import de.inetsoftware.classparser.LocalVariableTable;
 import de.inetsoftware.classparser.MethodInfo;
@@ -51,16 +53,32 @@ public abstract class ModuleWriter implements Closeable {
     private String               sourceFile;
 
     /**
-     * Write the content of the class to the
+     * Prepare the content of the class.
      * 
      * @param classFile
      *            the class file
-     * @throws IOException
-     *             if any I/O error occur
      * @throws WasmException
      *             if some Java code can't converted
      */
-    public void write( ClassFile classFile ) throws IOException, WasmException {
+    public void prepare( ClassFile classFile ) {
+        iterateMethods( classFile, m -> prepareMethod( m ) );
+    }
+
+    /**
+     * Write the content of the class to the writer.
+     * 
+     * @param classFile
+     *            the class file
+     * @throws WasmException
+     *             if some Java code can't converted
+     */
+    public void write( ClassFile classFile ) throws WasmException {
+        iterateMethods( classFile, m -> writeMethod( m ) );
+    }
+
+    private void iterateMethods( ClassFile classFile, Consumer<MethodInfo> handler ) throws WasmException {
+        sourceFile = null; // clear previous value for the case an IO exception occur
+        try {
             sourceFile = classFile.getSourceFile();
             if( sourceFile == null ) {
                 sourceFile = classFile.getThisClass().getName();
@@ -72,8 +90,23 @@ public abstract class ModuleWriter implements Closeable {
                                 && code.isSuperInitReturn( classFile.getSuperClass() ) ) {
                     continue; //default constructor
                 }
-            writeMethod( method );
+                handler.accept( method );
             }
+        } catch( IOException ioex ) {
+            throw WasmException.create( ioex, sourceFile, -1 );
+        }
+    }
+
+    /**
+     * Prepare the method.
+     * 
+     * @param method
+     *            the method
+     * @throws WasmException
+     *             if some Java code can't converted
+     */
+    private void prepareMethod( MethodInfo method ) throws WasmException {
+        
     }
 
     /**
@@ -81,12 +114,11 @@ public abstract class ModuleWriter implements Closeable {
      * 
      * @param method
      *            the method
-     * @throws IOException
-     *             if any I/O error occur
      * @throws WasmException
      *             if some Java code can't converted
      */
-    private void writeMethod( MethodInfo method ) throws IOException, WasmException {
+    private void writeMethod( MethodInfo method ) throws WasmException {
+        try {
             Code code = method.getCode();
             if( code != null ) { // abstract methods and interface methods does not have code
                 String methodName = method.getName(); // TODO naming conversion rule
@@ -116,13 +148,20 @@ public abstract class ModuleWriter implements Closeable {
                 }
                 writeMethodFinish( locals );
             }
+        } catch( IOException ioex ) {
+            throw WasmException.create( ioex, sourceFile, -1 );
+        }
     }
 
     /**
      * Look for a Export annotation and if there write an export directive.
+     * 
      * @param methodName
+     *            the normalized method name
      * @param method
+     *            the moethod
      * @throws IOException
+     *             if any IOException occur
      */
     private void writeExport( String methodName, MethodInfo method ) throws IOException {
         Annotations annotations = method.getRuntimeInvisibleAnnotations();