java io系列24之 BufferedWriter(字符缓冲输出流)

package java.io; public class BufferedWriter extends Writer { // 输出流对象
private Writer out; // 保存“缓冲输出流”数据的字符数组
private char cb[]; // nChars 是cb缓冲区中字符的总的个数
// nextChar 是下一个要读取的字符在cb缓冲区中的位置
private int nChars, nextChar; // 默认字符缓冲区大小
private static int defaultCharBufferSize = 8192; // 行分割符
private String lineSeparator; // 构造函数，传入“Writer对象”，默认缓冲区大小是8k
public BufferedWriter(Writer out) {
this(out, defaultCharBufferSize);
} // 构造函数，传入“Writer对象”，指定缓冲区大小是sz
public BufferedWriter(Writer out, int sz) {
super(out);
if (sz <= 0)
throw new IllegalArgumentException("Buffer size <= 0");
this.out = out;
cb = new char[sz];
nChars = sz;
nextChar = 0; lineSeparator = java.security.AccessController.doPrivileged(
new sun.security.action.GetPropertyAction("line.separator"));
} // 确保“BufferedWriter”是打开状态
private void ensureOpen() throws IOException {
if (out == null)
throw new IOException("Stream closed");
} // 对缓冲区执行flush()操作，将缓冲区的数据写入到Writer中
void flushBuffer() throws IOException {
synchronized (lock) {
ensureOpen();
if (nextChar == 0)
return;
out.write(cb, 0, nextChar);
nextChar = 0;
}
} // 将c写入到缓冲区中。先将c转换为char，然后将其写入到缓冲区。
public void write(int c) throws IOException {
synchronized (lock) {
ensureOpen();
// 若缓冲区满了，则清空缓冲，将缓冲数据写入到输出流中。
if (nextChar >= nChars)
flushBuffer();
cb[nextChar++] = (char) c;
}
} // 返回a，b中较小的数
private int min(int a, int b) {
if (a < b) return a;
return b;
} // 将字符数组cbuf写入到缓冲中，从cbuf的off位置开始写入，写入长度是len。
public void write(char cbuf[], int off, int len) throws IOException {
synchronized (lock) {
ensureOpen();
if ((off < 0) || (off > cbuf.length) || (len < 0) ||
((off + len) > cbuf.length) || ((off + len) < 0)) {
throw new IndexOutOfBoundsException();
} else if (len == 0) {
return;
} if (len >= nChars) {
/* If the request length exceeds the size of the output buffer,
flush the buffer and then write the data directly. In this
way buffered streams will cascade harmlessly. */
flushBuffer();
out.write(cbuf, off, len);
return;
} int b = off, t = off + len;
while (b < t) {
int d = min(nChars - nextChar, t - b);
System.arraycopy(cbuf, b, cb, nextChar, d);
b += d;
nextChar += d;
if (nextChar >= nChars)
flushBuffer();
}
}
} // 将字符串s写入到缓冲中，从s的off位置开始写入，写入长度是len。
public void write(String s, int off, int len) throws IOException {
synchronized (lock) {
ensureOpen(); int b = off, t = off + len;
while (b < t) {
int d = min(nChars - nextChar, t - b);
s.getChars(b, b + d, cb, nextChar);
b += d;
nextChar += d;
if (nextChar >= nChars)
flushBuffer();
}
}
} // 将换行符写入到缓冲中
public void newLine() throws IOException {
write(lineSeparator);
} // 清空缓冲区数据
public void flush() throws IOException {
synchronized (lock) {
flushBuffer();
out.flush();
}
} public void close() throws IOException {
synchronized (lock) {
if (out == null) {
return;
}
try {
flushBuffer();
} finally {
out.close();
out = null;
cb = null;
}
}
}
}