JavaIO<18>字符缓冲输出流BufferedWriter
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);
}
}