Java IO：CharArrayReader使用及源码分析

使用方法

　　CharArrayReader即字符数组输入流，用于从输入流读取字符，和ByteArrayInputStream的区别就是前者以字符为单位后者是字节。

方法介绍

　　CharArrayReader提供的API如下：

//构造方法
CharArrayReader(char[] buf)
CharArrayReader(char[] buf, int offset, int length)
//关闭输入流
void      close()
//mark
void      mark(int readLimit)
boolean   markSupported()
//读取下一个字符
int       read()
//读取多个字符
int       read(char[] b, int off, int len)
//是否可读
boolean   ready()
//返回mark的位置
void      reset()
//跳过n个字符
long      skip(long n)

使用示例

public void testCharArrayReader() {
try {
char [] letters = {'a','b','c','d','e','f','g','h','i','j','k','l','m','n'};
//创建输入流
CharArrayReader reader = new CharArrayReader(letters);
//读取第一个字符
System.out.printf("第一个字符为: %c\n", reader.read());
//mark
reader.mark(10);
//读取bcd到tmp
char [] tmp = new char[3];
reader.read(tmp, 0, 3);
System.out.println("读取三个字符到tmp: " + new String(tmp));
//读取reset后的第一个字符(b)
reader.reset();
System.out.printf("reset后第一个字符为: %c\n", reader.read());
} catch (Exception e) {
e.printStackTrace();
}
}

　　运行结果如下：

第一个字符为: a
读取三个字符到tmp: bcd
reset后第一个字符为: b

源码分析

构造方法

　　CharArrayReader的构造方法有两个，区别是初始化输入流的内容不同。

/**
* Creates a CharArrayReader from the specified array of chars.
* 以buf中所有字符初始化输入流
* @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.
* 以buf中部分字符为输入流
* @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();
}
//以buf中从offset开始length长度的字符初始化输入流
this.buf = buf;
this.pos = offset;
this.count = Math.min(offset + length, buf.length);
this.markedPos = offset;
}

read方法

　　read方法有读取下一个字符和读取多个字符两种重载方法，下面分析读取多个字符的源码。

/**
* Reads characters into a portion of an array.
* @param b  Destination buffer
* @param off  Offset at which to start storing characters
* @param len   Maximum number of characters to read
* @return  The actual number of characters read, or -1 if
*          the end of the stream has been reached
*
* @exception   IOException  If an I/O error occurs
*/
public int read(char b[], int off, int len) throws IOException {
synchronized (lock) {
ensureOpen(); //确保输入流正常
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) { //没有可读字符
return -1;
}
if (pos + len > count) { //可读字符不足len,只读剩下的字符
len = count - pos;
}
if (len <= 0) {
return 0;
}
System.arraycopy(buf, pos, b, off, len); //读取
pos += len;
return len;
}
}

参考：

[1] /article/4708118.html