BufferedWriter 源码分析

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转自：http://www.fengfly.com/plus/view-214074-1.html
BufferedWriter 是缓冲字符输出流。它继承于Writer。
BufferedWriter 的作用是为其他字符输出流添加一些缓冲功能。
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;              }          }      }  }
示例见原文
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