当一个java方法(无论是静态的还是非静态的)作为范围内的全局函数可用时,我们使用以下逻辑：

FunctionObject javascriptFunction = new FunctionObject(/* String*/ javascriptFunctionName, /* Method */ javaMethod, /*Scriptable */ parentScope);
boundScope.put(javascriptFunctionName, boundScope, javascriptFunction);

这里boundScope应该始终是使函数可用的范围.

但是,父作用域的值取决于我们是绑定实例方法还是静态方法.在静态方法的情况下,它可以是任何有意义的范围.它甚至可以与boundScope相同.

但是在实例方法的情况下,parentScope应该是其方法被绑定的实例.

以上只是背景信息.现在我将解释问题是什么,并为它提供一个自然的解决方案,即允许直接调用实例方法作为全局函数,而不是显式创建对象的实例,然后使用该实例调用方法.

调用函数时,Rhino调用FunctionObject.call()方法,该方法传递对此的引用.如果函数是一个全局函数,则调用它而不引用它(即xxx()而不是this.xxx()),传递给FunctionObject.call()方法的this变量的值是调用的范围(即在这种情况下,此参数的值将与scope参数的值相同).

如果调用的java方法是一个实例方法,这就成了一个问题,因为根据FunctionObject类的构造函数的JavaDocs：

如果该方法不是静态的,那么Java这个值将对应于JavaScript这个值.任何使用不具有正确Java类型的值调用该函数的尝试都将导致错误.

在上面描述的场景中就是这种情况. javascript此值与java此值不对应,并导致不兼容的对象错误.

解决方案是继承FunctionObject,重写call()方法,强制“修复”此引用,然后让调用正常进行.

所以类似于：

FunctionObject javascriptFunction = new MyFunctionObject(javascriptFunctionName, javaMethod, parentScope);
boundScope.put(javascriptFunctionName, boundScope, javascriptFunction);
private static class MyFunctionObject extends FunctionObject {
private MyFunctionObject(String name, Member methodOrConstructor, Scriptable parentScope) {
super(name, methodOrConstructor, parentScope);
}
@Override
public Object call(Context cx, Scriptable scope, Scriptable thisObj, Object[] args) {
return super.call(cx, scope, getParentScope(), args);
}
}

我认为最好用下面粘贴的自包含/完整示例来理解.在这个例子中,我们将实例方法公开：myJavaInstanceMethod(Double number)作为javascript范围内的全局函数(‘scriptExecutionScope’).因此,在这种情况下,’parentScope’参数的值必须是包含此方法的类的实例(即MyScriptable).

package test;
import org.mozilla.javascript.*;
import java.lang.reflect.Member;
import java.lang.reflect.Method;
//-- This is the class whose instance method will be made available in a JavaScript scope as a global function.
//-- It extends from ScriptableObject because instance methods of only scriptable objects can be directly exposed
//-- in a js scope as a global function.
public class MyScriptable extends ScriptableObject {
public static void main(String args[]) throws Exception {
Context.enter();
try {
//-- Create a top-level scope in which we will execute a simple test script to test if things are working or not.
Scriptable scriptExecutionScope = new ImporterTopLevel(Context.getCurrentContext());
//-- Create an instance of the class whose instance method is to be made available in javascript as a global function.
Scriptable myScriptable = new MyScriptable();
//-- This is not strictly required but it is a good practice to set the parent of all scriptable objects
//-- except in case of a top-level scriptable.
myScriptable.setParentScope(scriptExecutionScope);
//-- Get a reference to the instance method this is to be made available in javascript as a global function.
Method scriptableInstanceMethod = MyScriptable.class.getMethod("myJavaInstanceMethod", new Class[]{Double.class});
//-- Choose a name to be used for invoking the above instance method from within javascript.
String javascriptFunctionName = "myJavascriptGlobalFunction";
//-- Create the FunctionObject that binds the above function name to the instance method.
FunctionObject scriptableInstanceMethodBoundJavascriptFunction = new MyFunctionObject(javascriptFunctionName,
scriptableInstanceMethod, myScriptable);
//-- Make it accessible within the scriptExecutionScope.
scriptExecutionScope.put(javascriptFunctionName, scriptExecutionScope,
scriptableInstanceMethodBoundJavascriptFunction);
//-- Define a simple test script to test if things are working or not.
String testScript = "function simpleJavascriptFunction() {" +
" try {" +
" result = myJavascriptGlobalFunction(12.34);" +
" java.lang.System.out.println(result);" +
" }" +
" catch(e) {" +
" throw e;" +
" }" +
"}" +
"simpleJavascriptFunction();";
//-- Compile the test script.
Script compiledScript = Context.getCurrentContext().compileString(testScript, "My Test Script", 1, null);
//-- Execute the test script.
compiledScript.exec(Context.getCurrentContext(), scriptExecutionScope);
} catch (Exception e) {
throw e;
} finally {
Context.exit();
}
}
public Double myJavaInstanceMethod(Double number) {
return number * 2.0d;
}
@Override
public String getClassName() {
return getClass().getName();
}
private static class MyFunctionObject extends FunctionObject {
private MyFunctionObject(String name, Member methodOrConstructor, Scriptable parentScope) {
super(name, methodOrConstructor, parentScope);
}
@Override
public Object call(Context cx, Scriptable scope, Scriptable thisObj, Object[] args) {
return super.call(cx, scope, getParentScope(), args);
// return super.call(cx, scope, thisObj, args);
}
}
}

如果要查看修复后的行为,请取消注释第78行和注释第79行：

return super.call(cx, scope, getParentScope(), args);
//return super.call(cx, scope, thisObj, args);

如果你想看到没有修复的行为,那么注释第78行并取消注释第79行：

//return super.call(cx, scope, getParentScope(), args);
return super.call(cx, scope, thisObj, args);

希望这可以帮助.