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
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// 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)
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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 = ; // 行分割符 private String lineSeparator; // 构造函数，传入“Writer对象”，默认缓冲区大小是k 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 <= "); 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。
示例代码
关于BufferedWriter中API的详细用法，参考示例代码(BufferedWriterTest.java)：
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import java.io.BufferedWriter; import java.io.File; import java.io.OutputStream; import java.io.FileWriter; import java.io.IOException; import java.io.FileNotFoundException; import java.lang.SecurityException; import java.util.Scanner; /** * BufferedWriter 测试程序 * * */ public class BufferedWriterTest { private static final int LEN = 5; // 对应英文字母“abcdefghijklmnopqrstuvwxyz” //private static final char[] ArrayLetters = "abcdefghijklmnopqrstuvwxyz"; 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 main(String[] args) { testBufferedWriter() ; } /** * BufferedWriter的API测试函数 */ private static void testBufferedWriter() { // 创建“文件输出流”对应的BufferedWriter // 它对应缓冲区的大小是16，即缓冲区的数据>=16时，会自动将缓冲区的内容写入到输出流。 try { File file = new File("bufferwriter.txt"); BufferedWriter out = new BufferedWriter( new FileWriter(file)); // 将ArrayLetters数组的前10个字符写入到输出流中 out.write(ArrayLetters, 0, 10); // 将“换行符\n”写入到输出流中 out.write('\n'); out.flush(); //readUserInput() ; out.close(); } catch (FileNotFoundException e) { e.printStackTrace(); } catch (SecurityException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } } /** * 读取用户输入 */ 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); } } |
运行结果：
生成文件“bufferwriter.txt”，文件的内容是“abcdefghij”。
以上所述是小编给大家介绍的Java 中的 BufferedWriter知识，希望对大家有所帮助，如果大家有任何疑问请给我留言，小编会及时回复大家的。在此也非常感谢大家对服务器之家网站的支持！
