java学习笔记之BufferedReader与BufferedWriter

1. 使用缘由

为了提高字符流读写的效率，引入了缓冲机制，进行字符批量的读写，提高了单个字符读写的效率。BufferedReader用于加快读取字符的速度，BufferedWriter用于加快写入的速度

2. BufferedWriter

2.1 继承体系与方法

java.lang.Object
----java.io.Writer
------java.io.BufferedWriter

BufferedWriter(Writer out)
Creates a buffered character-output stream that uses a default-sized output buffer.
BufferedWriter(Writer out,  int sz）//sz可以指定缓冲区的大小
Creates a new buffered character-output stream that uses an output buffer of the given size

void close() Closes the stream, flushing it first.
void flush() Flushes the stream. //刷新缓存区
void newLine() Writes a line separator. //添加换行符
void write(char[] cbuf, int off, int len) Writes a portion of an array of characters. //写入指定的字符数组，off起始偏移量，len要写入的字符长度
void write(int c) Writes a single character.
void write(String s, int off, int len) Writes a portion of a String. //写入指定的字符串，off偏移量，len要 入的字符串长度

2.2实例代码

package ReaderWriter;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
/*
* @author pecu
*
*/
public class BufferedWriterReview {
public static void main(String[] args) {
//writeFile1();
writeFile2();

}

private static void writeFile2() {
BufferedWriter bw=null;
BufferedReader br=null;
try {
br = new BufferedReader(new FileReader("fw.txt"));
bw = new BufferedWriter(new FileWriter("bw2.txt"));
String buff=null;
while((buff=br.readLine())!=null){  //读取行，不包含换行符
//将读取的行内容写入文件，偏移量为0，写入长度为buff的长度
bw.write(buff, 0,buff.length());
bw.newLine(); // 添加换行
}
} catch (IOException e) {
e.printStackTrace();
}finally{
if(br!=null){
try {
br.close();
} catch (IOException e) {
e.printStackTrace();
}
}
if(bw!=null){
try {
bw.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}

}

private static void writeFile1() {
BufferedWriter bw=null;
BufferedReader br=null;
try {
br = new BufferedReader(new FileReader("fw.txt"));
bw = new BufferedWriter(new FileWriter("bw.txt"));
char buff[] = new char[1024];
int len;
while((len=br.read(buff))!=-1){
bw.write(buff, 0, len);
}
} catch (IOException e) {
e.printStackTrace();
}finally{
if(br!=null){
try {
br.close();
} catch (IOException e) {
e.printStackTrace();
}
}
if(bw!=null){
try {
bw.close()`

} catch (IOException e) {
e.printStackTrace();
}
}
}

}
}

3. BufferedReader

3.2 继承体系与方法

java.lang.Object
----java.io.Reader
----java.io.BufferedReader

1、BufferedReader(Reader in)
Creates a buffering character-input stream that uses a default-sized input buffer.
2、BufferedReader(Reader in, int sz)//sz可以指定缓冲区的大小
Creates a buffering character-input stream that uses an input buffer of the specified size.

void close() Closes the stream and releases any system resources associated with it.
int read() Reads a single character. //读取单个字符
int read(char[] cbuf, int off, int len) Reads characters into a portion of an array. //读取到cbuf，off开始存储的偏移量，len读取的长度
String readLine() Reads a line of text. //读取一行，不包含换行符
long skip(long n) Skips characters.//n为跳过的字符个数
boolean ready() Tells whether this stream is ready to be read.
void reset() Resets the stream to the most recent mark.

3.2 实例代码

package ReaderWriter;

import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
*
* @author pecu
*
*/
public class BufferedReaderReview {
public static void main(String[] args) {
readFile();
}

private static void readFile() {
FileReader fr=null;
BufferedReader br=null;
try {
fr=new FileReader("fw.txt");
br = new BufferedReader(fr);
String line=null;
while((line=br.readLine())!=null){//不包含 line-termination characters
System.out.println(line);
}
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}finally{
if(br!=null){
try {
br.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
}

4 自定义BufferedReader与BufferedWriter

/**
*
* @author pecu
*
*/
public class CustomBufferedReader extends Reader{
Reader r;
private char[] buff; // 字符缓冲区
private int lineNumber=0; // 行号
public CustomBufferedReader(Reader r) {
super();
this.r = r;
buff = new char[8192];
}

public int readInt() throws IOException{
return r.read();
}

public String readLine2() throws IOException {
int ch = 0;
StringBuffer sb = new StringBuffer();
synchronized (lock) {
while((ch=readInt()) != -1){
if(ch == '\r'){
continue;
}
if(ch == '\n'){
++lineNumber;
return sb.toString();
}
sb.append((char)ch);
}
}
if(sb.length()==0) return null;
++lineNumber;
return sb.toString();
}

public String readLine() throws IOException {
int ch = 0;
int count = 0;
synchronized (lock) {
while((ch=readInt()) != -1){  // 不到文件结尾
if(ch == '\r'){  // '\r'不存
continue;
}
if(ch == '\n' ){
++lineNumber;
return new String(buff,0,count);
}

buff[count++]= (char) ch;
}
}
if(count==0) return null;  //如果读取为空
++lineNumber;
return new String(buff,0,count);
}

public void close() throws IOException {
if (r!=null) {
r.close();
}
}

public int getLineNumber() {
return lineNumber;
}

@Override
public int read(char[] cbuf, int off, int len) throws IOException {
checkBounds(cbuf, off, len);
return r.read(cbuf, off, len);
}

/**
* 检查边界
*
* @param cbuf
* @param off
* @param len
*/
private void checkBounds(char[] cbuf, int off, int len) {
if (cbuf == null) {
throw new NullPointerException("cbuf is null");
}

if ((off < 0 || off > cbuf.length) || (len < 0 || len > cbuf.length)
|| (off + len) < 0 || (off + len) > cbuf.length) {
throw new ArrayIndexOutOfBoundsException();
}

if (0==len) {
return;
}
}
}

/**
* @author pecu
*/
public class CustomBufferedWriter extends Writer {
private static final String LINE_SEPARATOR = System
.getProperty("line.separator");
private Writer writer;
private static final int cacheSize = 8192; // 默认缓冲
private char buff[]; // 缓冲区
private int nChars, charIndex; //

public CustomBufferedWriter(Writer writer) {
this(writer, cacheSize);
}

public CustomBufferedWriter(Writer writer, int sz) {
super();
if (sz <= 0) {
throw new IllegalArgumentException("Buffered sz<=0");
}
this.writer = writer;
nChars = sz;
charIndex = 0;
buff = new char[sz];
}

public void newLine() throws IOException {
write(LINE_SEPARATOR);
// write(LINE_SEPARATOR,0,LINE_SEPARATOR.length());
}

public void write(int c) throws IOException {
if (charIndex >= nChars) {
flushBuffer();
}
buff[charIndex++] = (char) c;
}

public void write(String str) throws IOException{
write(str, 0, str.length());
}

@Override
public void write(String str, int off, int len) throws IOException {
securityCheck();
// 1
//      char[] charArray = str.toCharArray();
//      write(charArray, off, len);

// 2
while (len>0) {
int lenght=Math.min(nChars-charIndex, len);
str.getChars(off, off+lenght, buff, charIndex);
len-=lenght;
charIndex+=lenght;
if (charIndex>=nChars) {
flushBuffer();
}
}
}

@Override
public void write(char[] cbuf, int off, int len) throws IOException {
synchronized (lock) {
checkBounds(cbuf, off, len);
if (len>=nChars) {
flushBuffer();
writer.write(cbuf, 0, len);
return;
}

while (len>0) {
int length=Math.min(nChars-charIndex, len);
System.arraycopy(cbuf, off, buff, charIndex, length);
len-=length;
charIndex+=length;
if (charIndex>=nChars) {
flushBuffer();
}
}
}
}

/**
* 检查边界
*
* @param cbuf
* @param off
* @param len
*/
private void checkBounds(char[] cbuf, int off, int len) {
if (cbuf == null) {
throw new NullPointerException("cbuf is null");
}

if ((off < 0 || off > cbuf.length) || (len < 0 || len > cbuf.length)
|| (off + len) < 0 || (off + len) > cbuf.length) {
throw new ArrayIndexOutOfBoundsException();
}

if (0==len) {
return;
}
}

@Override
public void flush() throws IOException {
synchronized (lock) {
securityCheck();
flushBuffer();
writer.flush();
}
}

@Override
public void close() throws IOException {
synchronized (lock) {
securityCheck();
flush();
writer = null;
buff = null;
}
}

/**
* 刷新到字符流
*
* @throws IOException
*/
public void flushBuffer() throws IOException {
synchronized (lock) {
securityCheck();
if (charIndex == 0)
return;
writer.write(buff, 0, charIndex);
charIndex = 0;
}

}

/**
* 检查流是否关闭
*
* @throws IOException
*/
public void securityCheck() throws IOException {
if (writer == null) {
throw new IOException("stream closed");
}
}

}