Reader是Java IO体系里字符处理读取流的基本类,代码如下

/* * %W% %E% * * Copyright (c) 2006, Oracle and/or its affiliates. All rights reserved. * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms. */package java.io;/** * Abstract class for reading character streams.  The only methods that a * subclass must implement are read(char[], int, int) and close().  Most * subclasses, however, will override some of the methods defined here in order * to provide higher efficiency, additional functionality, or both. * * * @see BufferedReader * @see   LineNumberReader * @see CharArrayReader * @see InputStreamReader * @see   FileReader * @see FilterReader * @see   PushbackReader * @see PipedReader * @see StringReader * @see Writer * * @version     %I%, %E% * @author    Mark Reinhold * @since    JDK1.1 */public abstract class Reader implements Readable, Closeable {    /**     * 锁,在构造方法时赋值,默认使用this,也可以指定别的obj     */    protected Object lock;    /**     * Creates a new character-stream reader whose critical sections will     * synchronize on the reader itself.     */    protected Reader() {        this.lock = this;    }    /**     * Creates a new character-stream reader whose critical sections will     * synchronize on the given object.     *     * @param lock  The Object to synchronize on.     */    protected Reader(Object lock) {        if (lock == null) {            throw new NullPointerException();        }        this.lock = lock;    }    /**     * Attempts to read characters into the specified character buffer.     * The buffer is used as a repository of characters as-is: the only     * changes made are the results of a put operation. No flipping or     * rewinding of the buffer is performed.     *     * @param target the buffer to read characters into     * @return The number of characters added to the buffer, or      *         -1 if this source of characters is at its end     * @throws IOException if an I/O error occurs     * @throws NullPointerException if target is null     * @throws ReadOnlyBufferException if target is a read only buffer     * @since 1.5     */    public int read(java.nio.CharBuffer target) throws IOException {        int len = target.remaining();        char[] cbuf = new char[len];        int n = read(cbuf, 0, len);        if (n > 0)            target.put(cbuf, 0, n);        return n;    }    /**     * 读取一个字符,实现方式是先读取一个字符到一个char数组中,最后返回数组的第一个元素     */    public int read() throws IOException {        char cb[] = new char[1];        if (read(cb, 0, 1) == -1)            return -1;        else            return cb[0];    }    /**     * 读取char[]数组长度的字符到数组中     */    public int read(char cbuf[]) throws IOException {        return read(cbuf, 0, cbuf.length);    }    /**     * 交给子类实现的读取方法     */    abstract public int read(char cbuf[], int off, int len) throws IOException;    /** Maximum skip-buffer size */    private static final int maxSkipBufferSize = 8192;    /** 用来支持skip方法的数组 */    private char skipBuffer[] = null;    /**     * 跳过指定数目的字符,实现方式是将指定字符读取出来并丢弃     * 另外,这个方法是个串行方法     */    public long skip(long n) throws IOException {        if (n < 0L)            throw new IllegalArgumentException("skip value is negative");        int nn = (int) Math.min(n, maxSkipBufferSize);        synchronized (lock) {            if ((skipBuffer == null) || (skipBuffer.length < nn))                skipBuffer = new char[nn];            long r = n;            while (r > 0) {                int nc = read(skipBuffer, 0, (int)Math.min(r, nn));                if (nc == -1)                    break;                r -= nc;            }            return n - r;        }    }    /**     * 用来表示Reader中后面还有没有可读取的字符     * 在本类中始终返回false,在子类中有自己的实现     */    public boolean ready() throws IOException {        return false;    }    /**     * Tells whether this stream supports the mark() operation. The default     * implementation always returns false. Subclasses should override this     * method.     *     * @return true if and only if this stream supports the mark operation.     */    public boolean markSupported() {        return false;    }    /**     * 在指定位置做一个标记,用处类似于ByteBuffer中的mark     */    public void mark(int readAheadLimit) throws IOException {        throw new IOException("mark() not supported");    }    /**     * 将position设置为mark     */    public void reset() throws IOException {        throw new IOException("reset() not supported");    }    /**     * Closes the stream and releases any system resources associated with     * it.  Once the stream has been closed, further read(), ready(),     * mark(), reset(), or skip() invocations will throw an IOException.     * Closing a previously closed stream has no effect.     *     * @exception  IOException  If an I/O error occurs     */    abstract public void close() throws IOException;}

 

MultiReader

/* * Copyright (C) 2008 The Guava Authors * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */package com.google.common.io;import com.google.common.base.Preconditions;import java.io.IOException;import java.io.Reader;import java.util.Iterator;/** * 使用多个Reader合成一个MultiReader,其中Reader被Supplier包装起来 */class MultiReader extends Reader {    private final Iterator
     > it;    /** 当前Reader */    private Reader current;    MultiReader(Iterator
     > readers)            throws IOException {        this.it = readers;        advance();    }    /**     * 关闭当前Reader并跳到下一个reader     */    private void advance() throws IOException {        close();        if (it.hasNext()) {            current = it.next().getInput();        }    }    /**     * 读取当前Reader的内容到cbuf[]中,如果当前reader已经读完,则切换到下一个reader来读取     */    @Override public int read(char cbuf[], int off, int len) throws IOException {        if (current == null) {            return -1;        }        int result = current.read(cbuf, off, len);        if (result == -1) {            advance();            return read(cbuf, off, len);        }        return result;    }    /**     * 跳过指定个数目的字符,如果当前reader已经读完,则跳到下一个reader并重新读取     */    @Override public long skip(long n) throws IOException {        Preconditions.checkArgument(n >= 0, "n is negative");        if (n > 0) {            while (current != null) {                long result = current.skip(n);                if (result > 0) {                    return result;                }                advance();            }        }        return 0;    }    @Override public boolean ready() throws IOException {        return (current != null) && current.ready();    }    /**     * 关闭当前reader     */    @Override public void close() throws IOException {        if (current != null) {            try {                current.close();            } finally {                current = null;            }        }    }}