Java-IO之CharArrayReader

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CharArrayReader是字符数组输入流，CharArrayReader用于读取字符数组，继承于Reader操作的数据是以字符为单位。

（1）CharArrayReader实际上是通过字符数组去保存数据。

（2）在构造函数中有buf，我们通过buf来创建对象。

（3）read（）函数是读取下一个字符

CharArrayReader主要的函数：

CharArrayReader(char[] buf)CharArrayReader(char[] buf, int offset, int length)void      close()void      mark(int readLimit)boolean   markSupported()int       read()int       read(char[] buffer, int offset, int len)boolean   ready()void      reset()long      skip(long charCount)

示例代码：

public class CharArrayReaderTest {    private static final int LEN = 5;    // 对应英文字母“abcdefghijklmnopqrstuvwxyz”    private static final char[] ArrayLetters = new char[] {'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t',    'u','v','w','x','y','z'};    public static void main(String[] args) {        tesCharArrayReader() ;    }    /**     * CharArrayReader的API测试函数    */    private static void tesCharArrayReader() {        try {            // 创建CharArrayReader字符流，内容是ArrayLetters数组            CharArrayReader car = new CharArrayReader(ArrayLetters);            // 从字符数组流中读取5个字符            for (int i=0; i<LEN; i++) {                // 若能继续读取下一个字符，则读取下一个字符                if (car.ready() == true) {                    // 读取“字符流的下一个字符”                    char tmp = (char)car.read();                    System.out.printf("%d : %c\n", i, tmp);                }            }            // 若“该字符流”不支持标记功能，则直接退出            if (!car.markSupported()) {                System.out.println("make not supported!");                return ;            }            // 标记“字符流中下一个被读取的位置”。即--标记“f”，因为因为前面已经读取了5个字符，所以下一个被读取的位置是第6个字符”            // (01), CharArrayReader类的mark(0)函数中的“参数0”是没有实际意义的。            // (02), mark()与reset()是配套的，reset()会将“字符流中下一个被读取的位置”重置为“mark()中所保存的位置”            car.mark(0);            // 跳过5个字符。跳过5个字符后，字符流中下一个被读取的值应该是“k”。            car.skip(5);            // 从字符流中读取5个数据。即读取“klmno”            char[] buf = new char[LEN];            car.read(buf, 0, LEN);            System.out.printf("buf=%s\n", String.valueOf(buf));            // 重置“字符流”：即，将“字符流中下一个被读取的位置”重置到“mark()所标记的位置”，即f。            car.reset();            // 从“重置后的字符流”中读取5个字符到buf中。即读取“fghij”            car.read(buf, 0, LEN);            System.out.printf("buf=%s\n", String.valueOf(buf));        } catch (IOException e) {            e.printStackTrace();        }    }}

运行结果：

0 : a

1 : b

2 : c

3 : d

4 : e

buf=klmno

buf=fghij

基于JDK1.8的CharArrayReader源码分析：

public class CharArrayReader extends Reader {    /** The character buffer. */    //字符床缓冲数组    protected char buf[];    /** The current buffer position. */    //当前位置    protected int pos;    /** The position of mark in buffer. */    //标记位置    protected int markedPos = 0;    /**     *  The index of the end of this buffer.  There is not valid     *  data at or beyond this index.     */    //缓冲区使用的索引，超出这个索引无效    protected int count;    /**     * Creates a CharArrayReader from the specified array of chars.     * @param buf       Input buffer (not copied)     */    public CharArrayReader(char buf[]) {        this.buf = buf;        this.pos = 0;        this.count = buf.length;    }    /**     * Creates a CharArrayReader from the specified array of chars.     *     * <p> The resulting reader will start reading at the given     * <tt>offset</tt>.  The total number of <tt>char</tt> values that can be     * read from this reader will be either <tt>length</tt> or     * <tt>buf.length-offset</tt>, whichever is smaller.     *     * @throws IllegalArgumentException     *         If <tt>offset</tt> is negative or greater than     *         <tt>buf.length</tt>, or if <tt>length</tt> is negative, or if     *         the sum of these two values is negative.     *     * @param buf       Input buffer (not copied)     * @param offset    Offset of the first char to read     * @param length    Number of chars to read     */    public CharArrayReader(char buf[], int offset, int length) {        if ((offset < 0) || (offset > buf.length) || (length < 0) ||((offset + length) < 0)) {                    throw new IllegalArgumentException();        }        this.buf = buf;        this.pos = offset;        this.count = Math.min(offset + length, buf.length);        this.markedPos = offset;    }    /** Checks to make sure that the stream has not been closed */    private void ensureOpen() throws IOException {        if (buf == null)            throw new IOException("Stream closed");    }        //读单个字符    public int read() throws IOException {        synchronized (lock) {            ensureOpen();            if (pos >= count)                return -1;            else                return buf[pos++];        }    }    //读取数据并保存到b中，off其实位置，len是长度    public int read(char b[], int off, int len) throws IOException {        synchronized (lock) {            ensureOpen();            if ((off < 0) || (off > b.length) || (len < 0) ||((off + len) > b.length) || ((off + len) < 0)) {                    throw new IndexOutOfBoundsException();            } else if (len == 0) {                return 0;            }            if (pos >= count) {                return -1;            }            if (pos + len > count) {                len = count - pos;            }            if (len <= 0) {                return 0;            }            System.arraycopy(buf, pos, b, off, len);            pos += len;            return len;        }    }    //跳过n个字符    public long skip(long n) throws IOException {        synchronized (lock) {            ensureOpen();            if (pos + n > count) {                n = count - pos;            }            if (n < 0) {                return 0;            }            pos += n;            return n;        }    }    //是否可读    public boolean ready() throws IOException {        synchronized (lock) {            ensureOpen();            return (count - pos) > 0;        }    }    //是否支持标记    public boolean markSupported() {        return true;    }    //标记位置    public void mark(int readAheadLimit) throws IOException {        synchronized (lock) {            ensureOpen();            markedPos = pos;        }    }    //重置，位置为最近一次标记的位置    public void reset() throws IOException {        synchronized (lock) {            ensureOpen();            pos = markedPos;        }    }    //关闭资源，这边就是让字符数组为空    public void close() {        buf = null;    }}

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