Java MethodHandle.asCollector方法代碼示例

import java.lang.invoke.MethodHandle; //導入方法依賴的package包/類
private MethodHandle createRelinkAndInvokeMethod(final RelinkableCallSite callSite, final int relinkCount) {
    // Make a bound MH of invoke() for this linker and call site
    final MethodHandle boundRelinker = MethodHandles.insertArguments(RELINK, 0, this, callSite, Integer.valueOf(
            relinkCount));
    // Make a MH that gathers all arguments to the invocation into an Object[]
    final MethodType type = callSite.getDescriptor().getMethodType();
    final MethodHandle collectingRelinker = boundRelinker.asCollector(Object[].class, type.parameterCount());
    return MethodHandles.foldArguments(MethodHandles.exactInvoker(type), collectingRelinker.asType(
            type.changeReturnType(MethodHandle.class)));
}
 

import java.lang.invoke.MethodHandle; //導入方法依賴的package包/類
private void testArities(Class<? extends Object[]> cls,
                         int minArity,
                         int maxArity,
                         int iterations) throws Throwable {
    boolean verbose = (cls == Object[].class);
    for (int arity = minArity; arity <= maxArity; arity++) {
        if (verbose)  System.out.println("arity="+arity);
        MethodHandle mh = MH_hashArguments(cls, arity);
        MethodHandle mh_VA = mh.asSpreader(cls, arity);
        assert(mh_VA.type().parameterType(0) == cls);
        testArities(cls, arity, iterations, verbose, mh, mh_VA);
        // mh_CA will collect arguments of a particular type and pass them to mh_VA
        MethodHandle mh_CA = mh_VA.asCollector(cls, arity);
        MethodHandle mh_VA2 = mh_CA.asSpreader(cls, arity);
        assert(mh_CA.type().equals(mh.type()));
        assert(mh_VA2.type().equals(mh_VA.type()));
        if (cls != Object[].class) {
            try {
                mh_VA2.invokeWithArguments(new Object[arity]);
                throw new AssertionError("should not reach");
            } catch (ClassCastException | WrongMethodTypeException ex) {
            }
        }
        int iterations_VA = iterations / 100;
        testArities(cls, arity, iterations_VA, false, mh_CA, mh_VA2);
    }
}
 

import java.lang.invoke.MethodHandle; //導入方法依賴的package包/類
@Test
public static void testAsCollectorExample() throws Throwable {
    // test the JavaDoc asCollector-with-pos example
    StringWriter swr = new StringWriter();
    MethodHandle swWrite = LOOKUP.
            findVirtual(StringWriter.class, "write", methodType(void.class, char[].class, int.class, int.class)).
            bindTo(swr);
    MethodHandle swWrite4 = swWrite.asCollector(0, char[].class, 4);
    swWrite4.invoke('A', 'B', 'C', 'D', 1, 2);
    assertEquals("BC", swr.toString());
    swWrite4.invoke('P', 'Q', 'R', 'S', 0, 4);
    assertEquals("BCPQRS", swr.toString());
    swWrite4.invoke('W', 'X', 'Y', 'Z', 3, 1);
    assertEquals("BCPQRSZ", swr.toString());
}
 

import java.lang.invoke.MethodHandle; //導入方法依賴的package包/類
private void testArities(Class<? extends Object[]> cls,
                         int minArity,
                         int maxArity,
                         int iterations) throws Throwable {
    boolean verbose = (cls == Object[].class);
    for (int arity = minArity; arity <= maxArity; arity++) {
        if (verbose)  System.out.println("arity="+arity);
        MethodHandle mh = MH_hashArguments(cls, arity);
        MethodHandle mh_VA = mh.asSpreader(cls, arity);
        MethodHandle mh_VA_h = mh.asSpreader(0, cls, arity-1);
        assert(mh_VA.type().parameterType(0) == cls);
        assert(mh_VA_h.type().parameterType(0) == cls);
        testArities(cls, arity, iterations, verbose, mh, mh_VA, mh_VA_h);
        // mh_CA will collect arguments of a particular type and pass them to mh_VA
        MethodHandle mh_CA = mh_VA.asCollector(cls, arity);
        MethodHandle mh_VA2 = mh_CA.asSpreader(cls, arity);
        MethodHandle mh_VA2_h = mh_CA.asSpreader(0, cls, arity-1);
        assert(mh_CA.type().equals(mh.type()));
        assert(mh_VA2.type().equals(mh_VA.type()));
        if (cls != Object[].class) {
            try {
                mh_VA2.invokeWithArguments(new Object[arity]);
                throw new AssertionError("should not reach");
            } catch (ClassCastException | WrongMethodTypeException ex) {
            }
        }
        int iterations_VA = iterations / 100;
        testArities(cls, arity, iterations_VA, false, mh_CA, mh_VA2, mh_VA2_h);
    }
}
 

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

import java.lang.invoke.MethodHandle; //導入方法依賴的package包/類
/**
 * Creates a method handle out of the original target that will collect the varargs for the exact component type of
 * the varArg array. Note that this will nicely trigger language-specific type converters for exactly those varargs
 * for which it is necessary when later passed to linkerServices.convertArguments().
 *
 * @param target the original method handle
 * @param parameterCount the total number of arguments in the new method handle
 * @return a collecting method handle
 */
static MethodHandle collectArguments(final MethodHandle target, final int parameterCount) {
    final MethodType methodType = target.type();
    final int fixParamsLen = methodType.parameterCount() - 1;
    final Class<?> arrayType = methodType.parameterType(fixParamsLen);
    return target.asCollector(arrayType, parameterCount - fixParamsLen);
}