java.util.Spliterator# IMMUTABLE 源码实例Demo

/**
 * Returns an infinite sequential ordered {@code Stream} produced by iterative
 * application of a function {@code f} to an initial element {@code seed},
 * producing a {@code Stream} consisting of {@code seed}, {@code f(seed)},
 * {@code f(f(seed))}, etc.
 *
 * <p>The first element (position {@code 0}) in the {@code Stream} will be
 * the provided {@code seed}.  For {@code n > 0}, the element at position
 * {@code n}, will be the result of applying the function {@code f} to the
 * element at position {@code n - 1}.
 *
 * <p>The action of applying {@code f} for one element
 * <a href="../concurrent/package-summary.html#MemoryVisibility"><i>happens-before</i></a>
 * the action of applying {@code f} for subsequent elements.  For any given
 * element the action may be performed in whatever thread the library
 * chooses.
 *
 * @param <T> the type of stream elements
 * @param seed the initial element
 * @param f a function to be applied to the previous element to produce
 *          a new element
 * @return a new sequential {@code Stream}
 */
public static<T> Stream<T> iterate(final T seed, final UnaryOperator<T> f) {
    Objects.requireNonNull(f);
    Spliterator<T> spliterator = new Spliterators.AbstractSpliterator<>(Long.MAX_VALUE,
           Spliterator.ORDERED | Spliterator.IMMUTABLE) {
        T prev;
        boolean started;

        @Override
        public boolean tryAdvance(Consumer<? super T> action) {
            Objects.requireNonNull(action);
            T t;
            if (started)
                t = f.apply(prev);
            else {
                t = seed;
                started = true;
            }
            action.accept(prev = t);
            return true;
        }
    };
    return StreamSupport.stream(spliterator, false);
}
 

/**
 * Wrap the JDBC {@link ResultSet} as a stream object. Note that the stream has to be consumed within
 * the boundaries of the statement execution
 * @param rs
 * @return
 */
public Stream<Row> wrap(final ResultSet rs) throws SQLException {
    ResultSetMetaData md = rs.getMetaData();
    final String[] columnNames = new String[md.getColumnCount()];
    for (int i=0; i<columnNames.length; i++) {
        columnNames[i] = md.getColumnName(i+1);
    }
    
    Spliterator<Row> s = new Spliterators.AbstractSpliterator<Row>(Long.MAX_VALUE, Spliterator.NONNULL | Spliterator.IMMUTABLE) {

        @Override
        public boolean tryAdvance(Consumer<? super Row> action) {
            try {
                if (!rs.next()) {
                    return false;
                }
                
                // wrap the current result record as a Row which is then handed
                // off to the stream
                action.accept(new Row(rs, columnNames));
                return true;
            }
            catch (SQLException x) {
                // ouch
                logger.log(Level.SEVERE, x.getMessage(), x);
                return false;
            }
        }
    };
    
    // Create a sequential stream of the rows from the result set
    return StreamSupport.stream(s, false);
}
 

public int characteristics() {
    return (Spliterator.SIZED | Spliterator.SUBSIZED |
            Spliterator.NONNULL | Spliterator.IMMUTABLE);
}
 

public int characteristics() {
    return (Spliterator.SIZED | Spliterator.SUBSIZED |
            Spliterator.NONNULL | Spliterator.IMMUTABLE);
}
 

public int characteristics() {
    return (Spliterator.SIZED | Spliterator.SUBSIZED |
            Spliterator.NONNULL | Spliterator.IMMUTABLE);
}
 

@Override
public int characteristics() {
    return Spliterator.ORDERED | Spliterator.SIZED | Spliterator.SUBSIZED |
           Spliterator.IMMUTABLE | Spliterator.NONNULL |
           Spliterator.DISTINCT | Spliterator.SORTED;
}
 

@Override
public int characteristics() {
    return Spliterator.ORDERED | Spliterator.SIZED | Spliterator.SUBSIZED |
           Spliterator.IMMUTABLE | Spliterator.NONNULL |
           Spliterator.DISTINCT | Spliterator.SORTED;
}
 

@Override
public int characteristics() {
    return Spliterator.ORDERED | Spliterator.SIZED | Spliterator.SUBSIZED |
           Spliterator.IMMUTABLE | Spliterator.NONNULL |
           Spliterator.DISTINCT | Spliterator.SORTED;
}
 

@Override
public int characteristics() {
    return Spliterator.ORDERED | Spliterator.SIZED | Spliterator.SUBSIZED |
           Spliterator.IMMUTABLE | Spliterator.NONNULL |
           Spliterator.DISTINCT | Spliterator.SORTED;
}
 

@Override
public int characteristics() {
    return Spliterator.ORDERED | Spliterator.SIZED | Spliterator.SUBSIZED |
           Spliterator.IMMUTABLE | Spliterator.NONNULL |
           Spliterator.DISTINCT | Spliterator.SORTED;
}
 

public int characteristics() {
    return (Spliterator.SIZED | Spliterator.SUBSIZED |
            Spliterator.NONNULL | Spliterator.IMMUTABLE);
}
 

@Override
public int characteristics() {
    return Spliterator.ORDERED | Spliterator.SIZED | Spliterator.SUBSIZED |
           Spliterator.IMMUTABLE | Spliterator.NONNULL |
           Spliterator.DISTINCT | Spliterator.SORTED;
}
 

public int characteristics() {
    return (Spliterator.SIZED | Spliterator.SUBSIZED |
            Spliterator.NONNULL | Spliterator.IMMUTABLE);
}
 

@Override
public int characteristics() {
    return Spliterator.SIZED | Spliterator.SUBSIZED |
           Spliterator.ORDERED | Spliterator.IMMUTABLE;
}
 

public int characteristics() {
    return (Spliterator.SIZED | Spliterator.SUBSIZED |
            Spliterator.NONNULL | Spliterator.IMMUTABLE);
}
 

public int characteristics() {
    return (Spliterator.SIZED | Spliterator.SUBSIZED |
            Spliterator.NONNULL | Spliterator.IMMUTABLE);
}
 

@Override
public int characteristics() {
    return Spliterator.DISTINCT + Spliterator.NONNULL + Spliterator.IMMUTABLE;
}
 

@Override
public int characteristics() {
    return Spliterator.SIZED | Spliterator.SUBSIZED |
           Spliterator.ORDERED | Spliterator.IMMUTABLE;
}
 

/**
 * Returns a stream whose elements are the URLs of all the resources with
 * the given name. A resource is some data (images, audio, text, etc) that
 * can be accessed by class code in a way that is independent of the
 * location of the code.
 *
 * <p> The name of a resource is a {@code /}-separated path name that
 * identifies the resource.
 *
 * <p> The resources will be located when the returned stream is evaluated.
 * If the evaluation results in an {@code IOException} then the I/O
 * exception is wrapped in an {@link UncheckedIOException} that is then
 * thrown.
 *
 * <p> Resources in named modules are subject to the encapsulation rules
 * specified by {@link Module#getResourceAsStream Module.getResourceAsStream}.
 * Additionally, and except for the special case where the resource has a
 * name ending with "{@code .class}", this method will only find resources in
 * packages of named modules when the package is {@link Module#isOpen(String)
 * opened} unconditionally (even if the caller of this method is in the
 * same module as the resource). </p>
 *
 * @implSpec The default implementation invokes {@link #getResources(String)
 * getResources} to find all the resources with the given name and returns
 * a stream with the elements in the enumeration as the source.
 *
 * @apiNote When overriding this method it is recommended that an
 * implementation ensures that any delegation is consistent with the {@link
 * #getResource(java.lang.String) getResource(String)} method. This should
 * ensure that the first element returned by the stream is the same
 * resource that the {@code getResource(String)} method would return.
 *
 * @param  name
 *         The resource name
 *
 * @return  A stream of resource {@link java.net.URL URL} objects. If no
 *          resources could  be found, the stream will be empty. Resources
 *          for which a {@code URL} cannot be constructed, are in a package
 *          that is not opened unconditionally, or access to the resource
 *          is denied by the security manager, will not be in the stream.
 *
 * @throws  NullPointerException If {@code name} is {@code null}
 *
 * @since  9
 */
public Stream<URL> resources(String name) {
    Objects.requireNonNull(name);
    int characteristics = Spliterator.NONNULL | Spliterator.IMMUTABLE;
    Supplier<Spliterator<URL>> si = () -> {
        try {
            return Spliterators.spliteratorUnknownSize(
                getResources(name).asIterator(), characteristics);
        } catch (IOException e) {
            throw new UncheckedIOException(e);
        }
    };
    return StreamSupport.stream(si, characteristics, false);
}
 

/**
 * Returns a stream whose elements are the URLs of all the resources with
 * the given name. A resource is some data (images, audio, text, etc) that
 * can be accessed by class code in a way that is independent of the
 * location of the code.
 *
 * <p> The name of a resource is a {@code /}-separated path name that
 * identifies the resource.
 *
 * <p> The resources will be located when the returned stream is evaluated.
 * If the evaluation results in an {@code IOException} then the I/O
 * exception is wrapped in an {@link UncheckedIOException} that is then
 * thrown.
 *
 * <p> Resources in named modules are subject to the encapsulation rules
 * specified by {@link Module#getResourceAsStream Module.getResourceAsStream}.
 * Additionally, and except for the special case where the resource has a
 * name ending with "{@code .class}", this method will only find resources in
 * packages of named modules when the package is {@link Module#isOpen(String)
 * opened} unconditionally (even if the caller of this method is in the
 * same module as the resource). </p>
 *
 * @implSpec The default implementation invokes {@link #getResources(String)
 * getResources} to find all the resources with the given name and returns
 * a stream with the elements in the enumeration as the source.
 *
 * @apiNote When overriding this method it is recommended that an
 * implementation ensures that any delegation is consistent with the {@link
 * #getResource(java.lang.String) getResource(String)} method. This should
 * ensure that the first element returned by the stream is the same
 * resource that the {@code getResource(String)} method would return.
 *
 * @param  name
 *         The resource name
 *
 * @return  A stream of resource {@link java.net.URL URL} objects. If no
 *          resources could  be found, the stream will be empty. Resources
 *          for which a {@code URL} cannot be constructed, are in a package
 *          that is not opened unconditionally, or access to the resource
 *          is denied by the security manager, will not be in the stream.
 *
 * @throws  NullPointerException If {@code name} is {@code null}
 *
 * @since  9
 */
public Stream<URL> resources(String name) {
    Objects.requireNonNull(name);
    int characteristics = Spliterator.NONNULL | Spliterator.IMMUTABLE;
    Supplier<Spliterator<URL>> si = () -> {
        try {
            return Spliterators.spliteratorUnknownSize(
                getResources(name).asIterator(), characteristics);
        } catch (IOException e) {
            throw new UncheckedIOException(e);
        }
    };
    return StreamSupport.stream(si, characteristics, false);
}