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;
}
}