replace also a class with annotation

src/de/inetsoftware/classparser/ClassFile.java

@@ -34,8 +34,6 @@ import de.inetsoftware.classparser.Attributes.AttributeInfo;
  */
 public class ClassFile {
 
-    private final DataInputStream input;
-
     private final int             minorVersion;
 
     private final int             majorVersion;
@@ -71,7 +69,7 @@ public class ClassFile {
      *             if this input stream reaches the end before reading the class file.
      */
     public ClassFile( InputStream stream ) throws IOException {
-        this.input = new DataInputStream( stream );
+        DataInputStream input = new DataInputStream( stream );
         int magic = input.readInt();
         if( magic != 0xCAFEBABE ) {
             throw new IOException( "Invalid class magic: " + Integer.toHexString( magic ) );
@@ -87,8 +85,8 @@ public class ClassFile {
         for( int i = 0; i < interfaces.length; i++ ) {
             interfaces[i] = (ConstantClass)constantPool.get( input.readUnsignedShort() );
         }
-        fields = readFields();
-        methods = readMethods();
+        fields = readFields( input );
+        methods = readMethods( input );
         attributes = new Attributes( input, constantPool );
 
         stream.close();
@@ -117,6 +115,45 @@ public class ClassFile {
         }
     }
 
+    /**
+     * Create a replaced instance.
+     * 
+     * @param className
+     *            the class name that should be replaced
+     * @param classFile
+     *            the replacing class file data
+     */
+    public ClassFile( String className, ClassFile classFile ) {
+        minorVersion = classFile.minorVersion;
+        majorVersion = classFile.majorVersion;
+
+        constantPool = classFile.constantPool;
+        accessFlags = classFile.accessFlags;
+        thisClass = new ConstantClass( className );
+        superClass = classFile.superClass;
+        interfaces = classFile.interfaces;
+        fields = classFile.fields;
+        methods = classFile.methods;
+        attributes = classFile.attributes;
+
+        // patch constant pool
+        String origClassName = classFile.thisClass.getName();
+        for( int i = 0; i < constantPool.size(); i++ ) {
+            Object obj = constantPool.get( i );
+            if( obj instanceof ConstantClass ) {
+                if( ((ConstantClass)obj).getName().equals( origClassName ) ) {
+                    constantPool.set( i, thisClass );
+                }
+            } else if( obj instanceof ConstantFieldRef ) {
+                ConstantFieldRef ref = (ConstantFieldRef)obj;
+                if( ref.getClassName().equals( origClassName ) ) {
+                    ConstantNameAndType nameAndType = new ConstantNameAndType( ref.getName(), ref.getType() );
+                    constantPool.set( i, new ConstantFieldRef( thisClass, nameAndType ) );
+                }
+            }
+        }
+    }
+
     /**
      * Get value of SourceFile if available.
      *
@@ -216,7 +253,7 @@ public class ClassFile {
         return accessFlags;
     }
 
-    private FieldInfo[] readFields() throws IOException {
+    private FieldInfo[] readFields( DataInputStream input ) throws IOException {
         FieldInfo[] fields = new FieldInfo[input.readUnsignedShort()];
         for( int i = 0; i < fields.length; i++ ) {
             fields[i] = new FieldInfo( input, constantPool );
@@ -224,7 +261,7 @@ public class ClassFile {
         return fields;
     }
 
-    private MethodInfo[] readMethods() throws IOException {
+    private MethodInfo[] readMethods( DataInputStream input ) throws IOException {
         MethodInfo[] methods = new MethodInfo[input.readUnsignedShort()];
         for( int i = 0; i < methods.length; i++ ) {
             methods[i] = new MethodInfo( input, constantPool, this );

src/de/inetsoftware/classparser/ConstantPool.java

@@ -1,5 +1,5 @@
 /*
-   Copyright 2011 - 2019 Volker Berlin (i-net software)
+   Copyright 2011 - 2020 Volker Berlin (i-net software)
 
    Licensed under the Apache License, Version 2.0 (the "License");
    you may not use this file except in compliance with the License.
@@ -147,4 +147,25 @@ public class ConstantPool {
     public Object get( int index ) {
         return constantPool[index];
     }
+
+    /**
+     * Set a value in the constant pool.
+     * 
+     * @param index
+     *            the index
+     * @param value
+     *            the new value
+     */
+    void set( int index, Object value ) {
+        constantPool[index] = value;
+    }
+
+    /**
+     * Get the count of entries in the pool.
+     * 
+     * @return the count
+     */
+    int size() {
+        return constantPool.length;
+    }
 }

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

@@ -18,6 +18,7 @@ package de.inetsoftware.jwebassembly.module;
 
 import java.io.IOException;
 import java.io.InputStream;
+import java.util.HashMap;
 
 import javax.annotation.Nullable;
 
@@ -31,7 +32,9 @@ import de.inetsoftware.classparser.WeakValueCache;
  */
 public class ClassFileLoader {
 
-    private final WeakValueCache<String, ClassFile> CACHE = new WeakValueCache<>();
+    private final HashMap<String, ClassFile>        replace   = new HashMap<>();
+
+    private final WeakValueCache<String, ClassFile> weakCache = new WeakValueCache<>();
 
     private final ClassLoader                       loader;
 
@@ -56,16 +59,32 @@ public class ClassFileLoader {
      */
     @Nullable
     public ClassFile get( String className ) throws IOException {
-        ClassFile classFile = CACHE.get( className );
+        ClassFile classFile = replace.get( className );
+        if( classFile != null ) {
+            return classFile;
+        }
+        classFile = weakCache.get( className );
         if( classFile != null ) {
             return classFile;
         }
         InputStream stream = loader.getResourceAsStream( className + ".class" );
         if( stream != null ) {
             classFile = new ClassFile( stream );
-            CACHE.put( className, classFile );
+            weakCache.put( className, classFile );
         }
         return classFile;
     }
 
+    /**
+     * Replace the class in the cache with the given instance.
+     * 
+     * @param className
+     *            the name of the class to replace
+     * @param classFile
+     *            the replasing ClassFile
+     */
+    public void replace( String className, ClassFile classFile ) {
+        classFile = new ClassFile( className, classFile );
+        replace.put( className, classFile );
+    }
 }

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2017 - 2019 Volker Berlin (i-net software)
+ * Copyright 2017 - 2020 Volker Berlin (i-net software)
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -158,8 +158,19 @@ public class ModuleGenerator {
      *            the class file
      * @throws WasmException
      *             if some Java code can't converted
+     * @throws IOException
+     *             if any I/O error occur
      */
-    public void prepare( ClassFile classFile ) {
+    public void prepare( ClassFile classFile ) throws IOException {
+        // check if this class replace another class
+        Map<String,Object> annotationValues;
+        if( (annotationValues = classFile.getAnnotation( JWebAssembly.REPLACE_ANNOTATION )) != null ) {
+            String signatureName = (String)annotationValues.get( "value" );
+            if( signatureName != null ) {
+                classFileLoader.replace( signatureName, classFile );
+            }
+        }
+
         iterateMethods( classFile, m -> prepareMethod( m ) );
     }