Java MethodHandles.arrayElementGetter方法代碼示例

import java.lang.invoke.MethodHandles; //導入方法依賴的package包/類
/**
 * Returns a method handle to do an array load.
 * @param receiverClass Class of the array to load the value from
 * @return a MethodHandle that accepts the receiver as first argument, the index as second argument.
 *   It returns the loaded value.
 */
static MethodHandle lookupArrayLoad(Class<?> receiverClass) {
    if (receiverClass.isArray()) {
        return MethodHandles.arrayElementGetter(receiverClass);
    } else if (Map.class.isAssignableFrom(receiverClass)) {
        // maps allow access like mymap[key]
        return MAP_GET;
    } else if (List.class.isAssignableFrom(receiverClass)) {
        return LIST_GET;
    }
    throw new IllegalArgumentException("Attempting to address a non-array type " +
                                       "[" + receiverClass.getCanonicalName() + "] as an array.");
}
 

import java.lang.invoke.MethodHandles; //導入方法依賴的package包/類
@Override
public MethodHandle arrayElementGetter(final Class<?> type) {
    final MethodHandle mh = MethodHandles.arrayElementGetter(type);
    return debug(mh, "arrayElementGetter", type);
}
 

import java.lang.invoke.MethodHandles; //導入方法依賴的package包/類
private GuardedInvocationComponent getElementGetter(final CallSiteDescriptor callSiteDescriptor,
        final LinkerServices linkerServices, final List<String> operations) throws Exception {
    final MethodType callSiteType = callSiteDescriptor.getMethodType();
    final Class<?> declaredType = callSiteType.parameterType(0);
    final GuardedInvocationComponent nextComponent = getGuardedInvocationComponent(callSiteDescriptor,
            linkerServices, operations);

    // If declared type of receiver at the call site is already an array, a list or map, bind without guard. Thing
    // is, it'd be quite stupid of a call site creator to go though invokedynamic when it knows in advance they're
    // dealing with an array, or a list or map, but hey...
    // Note that for arrays and lists, using LinkerServices.asType() will ensure that any language specific linkers
    // in use will get a chance to perform any (if there's any) implicit conversion to integer for the indices.
    final GuardedInvocationComponent gic;
    final boolean isMap;
    if(declaredType.isArray()) {
        gic = new GuardedInvocationComponent(MethodHandles.arrayElementGetter(declaredType));
        isMap = false;
    } else if(List.class.isAssignableFrom(declaredType)) {
        gic = new GuardedInvocationComponent(GET_LIST_ELEMENT);
        isMap = false;
    } else if(Map.class.isAssignableFrom(declaredType)) {
        gic = new GuardedInvocationComponent(GET_MAP_ELEMENT);
        isMap = true;
    } else if(clazz.isArray()) {
        gic = getClassGuardedInvocationComponent(MethodHandles.arrayElementGetter(clazz), callSiteType);
        isMap = false;
    } else if(List.class.isAssignableFrom(clazz)) {
        gic = new GuardedInvocationComponent(GET_LIST_ELEMENT, Guards.asType(LIST_GUARD, callSiteType), List.class,
                ValidationType.INSTANCE_OF);
        isMap = false;
    } else if(Map.class.isAssignableFrom(clazz)) {
        gic = new GuardedInvocationComponent(GET_MAP_ELEMENT, Guards.asType(MAP_GUARD, callSiteType), Map.class,
                ValidationType.INSTANCE_OF);
        isMap = true;
    } else {
        // Can't retrieve elements for objects that are neither arrays, nor list, nor maps.
        return nextComponent;
    }

    // We can have "dyn:getElem:foo", especially in composites, i.e. "dyn:getElem|getProp|getMethod:foo"
    final String fixedKey = getFixedKey(callSiteDescriptor);
    // Convert the key to a number if we're working with a list or array
    final Object typedFixedKey;
    if(!isMap && fixedKey != null) {
        typedFixedKey = convertKeyToInteger(fixedKey, linkerServices);
        if(typedFixedKey == null) {
            // key is not numeric, it can never succeed
            return nextComponent;
        }
    } else {
        typedFixedKey = fixedKey;
    }

    final GuardedInvocation gi = gic.getGuardedInvocation();
    final Binder binder = new Binder(linkerServices, callSiteType, typedFixedKey);
    final MethodHandle invocation = gi.getInvocation();

    if(nextComponent == null) {
        return gic.replaceInvocation(binder.bind(invocation));
    }

    final MethodHandle checkGuard;
    if(invocation == GET_LIST_ELEMENT) {
        checkGuard = convertArgToInt(RANGE_CHECK_LIST, linkerServices, callSiteDescriptor);
    } else if(invocation == GET_MAP_ELEMENT) {
        // TODO: A more complex solution could be devised for maps, one where we do a get() first, and fold it
        // into a GWT that tests if it returned null, and if it did, do another GWT with containsKey()
        // that returns constant null (on true), or falls back to next component (on false)
        checkGuard = CONTAINS_MAP;
    } else {
        checkGuard = convertArgToInt(RANGE_CHECK_ARRAY, linkerServices, callSiteDescriptor);
    }
    final MethodPair matchedInvocations = matchReturnTypes(binder.bind(invocation),
            nextComponent.getGuardedInvocation().getInvocation());
    return nextComponent.compose(matchedInvocations.guardWithTest(binder.bindTest(checkGuard)), gi.getGuard(),
            gic.getValidatorClass(), gic.getValidationType());
}