java源码-BufferedWriter

开篇

BufferedWriter和BufferedReader是对称的，一并分析下源码。

源码分析

构造函数

• BufferedWriter的构造函数通过缓冲区char cb[]数组保存待持久化字符
• 缓存区默认大小为8192
• BufferedWriter跟BufferedReader一样采用装饰者模式进行设计，通过内部Writer out对象保存被装饰的Writer对象。
• BufferedWriter的写操作通过被装饰的out对象进行数据写入。

public class BufferedWriter extends Writer { private Writer out; private char cb[]; private int nChars, nextChar; private static int defaultCharBufferSize = 8192; private String lineSeparator; public BufferedWriter(Writer out) { this(out, defaultCharBufferSize); } 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")); } 

write过程

• write过程先把数据写到缓冲区cb数组当中
• 当缓冲区cb数组当中的字符超出最大缓存区大小，那么就执行flush保存数据

 public void write(int c) throws IOException { synchronized (lock) { ensureOpen(); // 超出缓存区大小就执行flush操作 if (nextChar >= nChars) flushBuffer(); cb[nextChar++] = (char) c; } } void flushBuffer() throws IOException { synchronized (lock) { ensureOpen(); if (nextChar == 0) return; // 将数据通过out对象进行持久化 out.write(cb, 0, nextChar); // 重置缓冲区的起始位置 nextChar = 0; } } } 

类依赖图

• BufferedWriter的类依赖图如下图，所有的io writer都是继承自Writer作为基类。