BufferedWriter 介绍
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。BufferedWriter 函数列表
// 构造函数 BufferedWriter(Writer out) BufferedWriter(Writer out, int sz) void close() // 关闭此流，但要先刷新它。 void flush() // 刷新该流的缓冲。 void newLine() // 写入一个行分隔符。 void write(char[] cbuf, int off, int len) // 写入字符数组的某一部分。 void write(int c) // 写入单个字符。 void write(String s, int off, int len) // 写入字符串的某一部分。
BufferedWriter 源码分析(基于jdk1.7.40)
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; } } } } 说明： BufferedWriter的源码非常简单，这里就BufferedWriter的思想进行简单说明：BufferedWriter通过字符数组来缓冲数据，当缓冲区满或者用户调用flush()函数时，它就会将缓冲区的数据写入到输出流中。 示例
package org.credo.jdk.io.readerAndWriter;import java.io.BufferedWriter;import java.io.File;import java.io.FileWriter;import java.io.IOException;import java.util.Scanner;public class BufferedWriterTest{ public static void main(String[] args) { try { testBufferedWriter(); } catch (IOException e) { e.printStackTrace(); } } 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 testBufferedWriter() throws IOException { File file = new File("bufferedreader.txt"); BufferedWriter bufferedWriter=new BufferedWriter(new FileWriter(file)); bufferedWriter.write(ArrayLetters); bufferedWriter.write('\n'); bufferedWriter.close(); readUserInput(); } private static void readUserInput() { System.out.println("please input a text:"); Scanner reader=new Scanner(System.in); // 等待一个输入 String str = reader.next(); System.out.printf("the input is : %s\n", str); } }