Subject:
JavaAdapter return type conversion
Date:
Wed, 19 Apr 2000 12:12:47 +0100
From:
Matthias Radestock <rade@logee.com>
Organization:
Logee
To:
norris@netscape.com
CC:
mccabe@netscape.com, beard@netscape.com, rogerl@netscape.com
Dear Rhino team,
When returning an array from a scripted Java object (i.e. a JS object
that implements a Java interface), no type conversion is performed, ie.
a NativeArray is returned instead of a Java array. Example:
Java:
interface Foo {
public String[] boo();
}
JS:
FooI = {
boo: function() { return ["Boo"];}
}
myFoo = new Packages.Foo(FooI);
myFoo.boo(); //==> breaks with a ClassCastException
Looking at the JavaAdapter code, there is no code for array conversion.
This is particularly bad because precisely such a conversion *does*
happen when calling a Java method from JS. So we end up with a
discrepancy.
See attachment for a patch to fix this and little test program. The
patch works by calling the coerceType function on NativeJavaObject,
which is the function responsible for doing the conversion when calling
from JS to Java. I've simplified the code so that this function gets
called for all non-primitive return type, not just arrays. There are
probably more efficient solutions but I'm not a Java bytecode hacker.
Matthias
PS: I didn't open a bug for this because I wasn't sure whether you guys
would agree that this is indeed a problem ;)
public interface JSReturnTest {
public boolean returnBoolean();
public char returnChar();
public int returnInt();
public String returnString();
public org.mozilla.javascript.Scriptable returnScriptable();
public Object returnObject();
public boolean[] returnBooleanA();
public char[] returnCharA();
public int[] returnIntA();
public String[] returnStringA();
public org.mozilla.javascript.Scriptable[] returnScriptableA();
public Object[] returnObjectA();
public Object[][] returnObjectAA();
}
Index: JavaAdapter.java
===================================================================
RCS file: /cvsroot/mozilla/js/rhino/org/mozilla/javascript/JavaAdapter.java,v
retrieving revision 1.21
diff -r1.21 JavaAdapter.java
54c54,59
<
---
>
> public static Object convertResult(Object result, String classname)
> throws ClassNotFoundException {
> return NativeJavaObject.coerceType(Class.forName(classname),
> result);
> }
467,474c472,474
< } else if (retType.equals(String.class)) {
< cfw.add(ByteCode.INVOKESTATIC,
< "org/mozilla/javascript/Context",
< "toString", "(Ljava/lang/Object;)",
< "Ljava/lang/String;");
< cfw.add(ByteCode.ARETURN);
< } else if (retType.equals(Scriptable.class)) {
< cfw.add(ByteCode.ALOAD_0); // load 'this' to find scope from
---
> } else {
> String retTypeStr = retType.getName();
> cfw.addLoadConstant(retTypeStr);
476,477c476,477
< "org/mozilla/javascript/Context",
< "toObject",
---
> "org/mozilla/javascript/JavaAdapter",
> "convertResult",
479,500c479,480
< "Lorg/mozilla/javascript/Scriptable;)",
< "Lorg/mozilla/javascript/Scriptable;");
< cfw.add(ByteCode.ARETURN);
< } else {
< // If it is a wrapped type, cast to Wrapper and call unwrap()
< cfw.add(ByteCode.DUP);
< cfw.add(ByteCode.INSTANCEOF, "org/mozilla/javascript/Wrapper");
< // skip 3 for IFEQ, 3 for CHECKCAST, and 5 for INVOKEINTERFACE
< cfw.add(ByteCode.IFEQ, 11);
< cfw.add(ByteCode.CHECKCAST, "org/mozilla/javascript/Wrapper");
< cfw.add(ByteCode.INVOKEINTERFACE,
< "org/mozilla/javascript/Wrapper",
< "unwrap", "()", "Ljava/lang/Object;");
<
< // If Undefined, return null
< cfw.add(ByteCode.DUP);
< cfw.add(ByteCode.INSTANCEOF, "org/mozilla/javascript/Undefined");
< // skip 3 for IFEQ, 1 for ACONST_NULL, 1 for ARETURN
< cfw.add(ByteCode.IFEQ, 5);
< cfw.add(ByteCode.ACONST_NULL);
< cfw.add(ByteCode.ARETURN);
<
---
> "Ljava/lang/String;)",
> "Ljava/lang/Object;");
502,503c482
< String retTypeStr = retType.getName().replace('.', '/');
< cfw.add(ByteCode.CHECKCAST, retTypeStr);
---
> cfw.add(ByteCode.CHECKCAST, retTypeStr.replace('.', '/'));
testpatch.js
Name:
testpatch.js
Type:
JavaScript Program (application/x-javascript)
Encoding:
7bit
