d明白Java的IOpȝ
一Q?Input和Output
1. stream代表的是M有能力出数据的数据源，或是M有能力接收数据的接收源。在Java的IO中，所有的streamQ包括Input和Out streamQ都包括两种cdQ?br /> 1.1 以字节ؓ导向的stream
以字节ؓ导向的streamQ表CZ字节为单位从stream中读取或往stream中写入信息。以字节为导向的stream包括下面几种cdQ?br /> 1) input streamQ?br /> 1) ByteArrayInputStreamQ把内存中的一个缓冲区作ؓInputStream使用
2) StringBufferInputStreamQ把一个String对象作ؓInputStream
3) FileInputStreamQ把一个文件作为InputStreamQ实现对文g的读取操?br /> 4) PipedInputStreamQ实Cpipe的概念，主要在线E中使用
5) SequenceInputStreamQ把多个InputStream合ƈZ个InputStream
2) Out stream
1) ByteArrayOutputStreamQ把信息存入内存中的一个缓冲区?br /> 2) FileOutputStreamQ把信息存入文g?br /> 3) PipedOutputStreamQ实Cpipe的概念，主要在线E中使用
4) SequenceOutputStreamQ把多个OutStream合ƈZ个OutStream
1.2 以Unicode字符为导向的stream
以Unicode字符为导向的streamQ表CZUnicode字符为单位从stream中读取或往stream中写入信息。以Unicode字符为导向的stream包括下面几种cdQ?br /> 1) Input Stream
1) CharArrayReaderQ与ByteArrayInputStream对应
2) StringReaderQ与StringBufferInputStream对应
3) FileReaderQ与FileInputStream对应
4) PipedReaderQ与PipedInputStream对应
2) Out Stream
1) CharArrayWriteQ与ByteArrayOutputStream对应
2) StringWriteQ无与之对应的以字节为导向的stream
3) FileWriteQ与FileOutputStream对应
4) PipedWriteQ与PipedOutputStream对应
以字Wؓ导向的stream基本上对有与之相对应的以字节为导向的stream。两个对应类实现的功能相同，字是在操作时的导向不同。如CharArrayReaderQ和ByteArrayInputStream的作用都是把内存中的一个缓冲区作ؓInputStream使用Q所不同的是前者每ơ从内存中读取一个字节的信息Q而后者每ơ从内存中读取一个字W?br /> 1.3 两种不现导向的stream之间的{?br /> InputStreamReader和OutputStreamReaderQ把一个以字节为导向的stream转换成一个以字符为导向的stream?br /> 2. streamd属?br /> 2.1 “为streamd属?#8221;的作?br /> q用上面介绍的Java中操作IO的APIQ我们就可完成我们想完成的Q何操作了。但通过FilterInputStream和FilterOutStream的子c，我们可以为streamd属性。下面以一个例子来说明q种功能的作用?br /> 如果我们要往一个文件中写入数据Q我们可以这h作：
FileOutStream fs = new FileOutStream(“test.txt”);
然后可以通过产生的fs对象调用write()函数来往test.txt文g中写入数据了。但是，如果我们惛_?#8220;先把要写入文件的数据先缓存到内存中，再把~存中的数据写入文g?#8221;的功能时Q上面的API没有一个能满我们的需求了。但是通过FilterInputStream和FilterOutStream的子c，为FileOutStreamd我们所需要的功能?br /> 2.2 FilterInputStream的各U类?br /> 2.2.1 用于装以字节ؓ导向的InputStream
1) DataInputStreamQ从stream中读取基本类型（int、char{）数据?br /> 2) BufferedInputStreamQ用缓冲区
3) LineNumberInputStreamQ会记录input stream内的行数Q然后可以调用getLineNumber()和setLineNumber(int)
4) PushbackInputStreamQ很用刎ͼ一般用于编译器开?br /> 2.2.2 用于装以字Wؓ导向的InputStream
1) 没有与DataInputStream对应的类。除非在要用readLine()时改用BufferedReaderQ否则用DataInputStream
2) BufferedReaderQ与BufferedInputStream对应
3) LineNumberReaderQ与LineNumberInputStream对应
4) PushBackReaderQ与PushbackInputStream对应
2.3 FilterOutStream的各U类?br /> 2.2.3 用于装以字节ؓ导向的OutputStream
1) DataIOutStreamQ往stream中输出基本类型（int、char{）数据?br /> 2) BufferedOutStreamQ用缓冲区
3) PrintStreamQ生格式化输出
2.2.4 用于装以字Wؓ导向的OutputStream
1) BufferedWriteQ与对应
2) PrintWriteQ与对应
3. RandomAccessFile
1) 可通过RandomAccessFile对象完成Ҏ件的d操作
2) 在生一个对象时Q可指明要打开的文件的性质QrQ只读；wQ只写；rw可读?br /> 3) 可以直接跛_文g中指定的位置
4. I/O应用的一个例?br /> import java.io.*;
public class TestIO{
public static void main(String[] args)
throws IOException{
//1.以行为单位从一个文件读取数?br /> BufferedReader in =
new BufferedReader(
new FileReader("F:\\nepalon\\TestIO.java"));
String s, s2 = new String();
while((s = in.readLine()) != null)
s2 += s + "\n";
in.close();
//1b. 接收键盘的输?br /> BufferedReader stdin =
new BufferedReader(
new InputStreamReader(System.in));
System.out.println("Enter a line:");
System.out.println(stdin.readLine());
//2. 从一个String对象中读取数?br /> StringReader in2 = new StringReader(s2);
int c;
while((c = in2.read()) != -1)
System.out.println((char)c);
in2.close();
//3. 从内存取出格式化输入
try{
DataInputStream in3 =
new DataInputStream(
new ByteArrayInputStream(s2.getBytes()));
while(true)
System.out.println((char)in3.readByte());
}
catch(EOFException e){
System.out.println("End of stream");
}
//4. 输出到文?br /> try{
BufferedReader in4 =
new BufferedReader(
new StringReader(s2));
PrintWriter out1 =
new PrintWriter(
new BufferedWriter(
new FileWriter("F:\\nepalon\\ TestIO.out")));
int lineCount = 1;
while((s = in4.readLine()) != null)
out1.println(lineCount++ + "Q? + s);
out1.close();
in4.close();
}
catch(EOFException ex){
System.out.println("End of stream");
}
//5. 数据的存储和恢复
try{
DataOutputStream out2 =
new DataOutputStream(
new BufferedOutputStream(
new FileOutputStream("F:\\nepalon\\ Data.txt")));
out2.writeDouble(3.1415926);
out2.writeChars("\nThas was pi:writeChars\n");
out2.writeBytes("Thas was pi:writeByte\n");
out2.close();
DataInputStream in5 =
new DataInputStream(
new BufferedInputStream(
new FileInputStream("F:\\nepalon\\ Data.txt")));
BufferedReader in5br =
new BufferedReader(
new InputStreamReader(in5));
System.out.println(in5.readDouble());
System.out.println(in5br.readLine());
System.out.println(in5br.readLine());
}
catch(EOFException e){
System.out.println("End of stream");
}
//6. 通过RandomAccessFile操作文g
RandomAccessFile rf =
new RandomAccessFile("F:\\nepalon\\ rtest.dat", "rw");
for(int i=0; i<10; i++)
rf.writeDouble(i*1.414);
rf.close();
rf = new RandomAccessFile("F:\\nepalon\\ rtest.dat", "r");
for(int i=0; i<10; i++)
System.out.println("Value " + i + "Q? + rf.readDouble());
rf.close();
rf = new RandomAccessFile("F:\\nepalon\\ rtest.dat", "rw");
rf.seek(5*8);
rf.writeDouble(47.0001);
rf.close();
rf = new RandomAccessFile("F:\\nepalon\\ rtest.dat", "r");
for(int i=0; i<10; i++)
System.out.println("Value " + i + "Q? + rf.readDouble());
rf.close();
}
}
关于代码的解释（以区为单位）Q?br /> 1ZQ当d文gӞ先把文g内容d~存中，当调用in.readLine()Ӟ再从~存中以字符的方式读取数据（以下U?#8220;~存字节d方式”Q?br /> 1bZQ由于想以缓存字节读取方式从标准IOQ键盘）中读取数据，所以要先把标准IOQSystem.inQ{换成字符导向的streamQ再q行BufferedReader装?br /> 2ZQ要以字W的形式从一个String对象中读取数据，所以要产生一个StringReadercd的stream?br /> 4ZQ对String对象s2d数据Ӟ先把对象中的数据存入~存中，再从~冲中进行读取；对TestIO.out文gq行操作Ӟ先把格式化后的信息输出到~存中，再把~存中的信息输出到文件中?br /> 5ZQ对Data.txt文gq行输出Ӟ是先把基本类型的数据输出屋缓存中Q再把缓存中的数据输出到文g中；Ҏ件进行读取操作时Q先把文件中的数据读取到~存中，再从~存中以基本cd的Ş式进行读取。注意in5.readDouble()q一行。因为写入第一个writeDouble()Q所以ؓ了正显C。也要以基本cd的Ş式进行读取?br /> 6区是通过RandomAccessFilecd文gq行操作?br />
----
重要提示Q?br />
LineNumberInputStreamQStringBufferInputStream已经废除Q大家不要再用！
StringBufferInputStreamQThis class does not properly convert characters into bytesQ?br />
StringBufferInputStreamQDeprecated. This class incorrectly assumes that bytes adequately represent charactersQ?br />
----------------兛_IOQ就是关心你的JAVA前途之路！-----------------------
DataInputStream中已经没有readLine()整个ҎQ?br />
替换为： BufferedReader d=new BufferedReader(new InputStreamReader(in));
--------把字节流转换为字W流接入~存d字符中Q再q行处理Q?br />
q个Ҏ很大的优势！
----------------------
-----------------Why use character streams?------------------
The primary advantage of character streams is that they make it easy to write programs that are not dependent upon a specific character encoding, and are therefore easy to internationalize.
Java stores strings in Unicode, an international standard character encoding that is capable of representing most of the world's written languages. Typical user-readable text files, however, use encodings that are not necessarily related to Unicode, or even to ASCII, and there are many such encodings. Character streams hide the complexity of dealing with these encodings by providing two classes that serve as bridges between byte streams and character streams. The InputStreamReader class implements a character-input stream that reads bytes from a byte-input stream and converts them to characters according to a specified encoding. Similarly, the OutputStreamWriter class implements a character-output stream that converts characters into bytes according a specified encoding and writes them to a byte-output stream.
A second advantage of character streams is that they are potentially much more efficient than byte streams. The implementations of many of Java's original byte streams are oriented around byte-at-a-time read and write operations. The character-stream classes, in contrast, are oriented around buffer-at-a-time read and write operations. This difference, in combination with a more efficient locking scheme, allows the character stream classes to make up for the added overhead of encoding conversion in many cases.
----------标准讑֤System.ind数据------------------
-----------------------------------------------------
d字节QBufferedInputStream
d字符QBufferedReader + InputStreamReader
----------------------------------------------
import java.io.*;
public class systemin
{
public static void main(String args[])
{ try{ //{换！
BufferedReader is=new BufferedReader(new InputStreamReader(System.in))
String inputline=null;
while((inputline=is.readLine())!=null)
System.out.println(inputline);
is.close();
}
catch(IOException e)
{ System,out.println("IOXE: "+e);
}
}
}
--------------------------------------------------------------------------------
-----------------标准输出System.out是一个打印流PrintStream---------------------
import java.io.*;
public class PrintStandardOutput {
public static void main(String[] args) {
String myAnswer = "No, and that's final,";
System.out.println("Hello World of Java");
System.out.println("The answer is " + myAnswer + " at this time.");
PrintWriter pw = new PrintWriter(System.out);
pw.println("The answer is " + myAnswer + " at this time.");
int i = 42;
pw.println(i + '=' + " the answer.");
pw.println("Note: " + i + '=' + " the answer.");
pw.println(i + "=" + " the answer.");
pw.println(i + ('=' + " the answer."));
pw.close();
}
}
-----------------------------------------------------------------------------------
-----------------------要读?输出到—）一个文本文?----------------------------
BufferedReader is=new BufferedReader(new FileReader("xxxx.text"));d
BufferedOutputStream byteout=new BufferedOutputStream(new FileOutputStream("XX.dat"));
// 写出到文本！
-----------------------------------------------
---------------利用 BufferedReader--FileReaderd文本文gQ?----------
---------------在IO中始l要注意是字节流q是字符?---------------------
-----------------------------------------------------------------------
import java.io.*;
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
class filewindow extends JFrame implements ActionListener
{
JTextArea text;
BufferedReader in;
JButton button;
FileReader file;
filewindow()
{
super("文g字符?);
Container con=getContentPane();
text=new JTextArea(50,50);
text.setBackground(Color.blue);
try{
File f=new File("E:\\a.txt");
file=new FileReader(f);
in=new BufferedReader(file);
/**BufferedReaderQReader in)构造函敎ͼ
*文g自字W读取流FileReader接入BufferedReader
*中Q以便用BufferedReader的对象方法readLine()高效成行dQ?br />
*/
}
catch(FileNotFoundException e){}
catch(IOException e){}
button=new JButton("d");
button.addActionListener(this);
con.setLayout(new BorderLayout());
setSize(300,200);
setVisible(true);
con.add(text,"Center");
con.add(button,"South");
addWindowListener(new WindowAdapter()
{public void windowClosing(WindowEvent e)
{setVisible(false);System.exit(0);}});
}
public void actionPerformed(ActionEvent e)
{
String s;
if(e.getSource()==button)
try{
while((s=in.readLine())!=null)
text.append(s+'\n');
//在这里大家还可以用BufferString来暂时保存读取的字符数据Q?br />
}
catch(IOException e1){}
}
//---------main()----------
public static void main(String args[])
{
filewindow win=new filewindow();
win.pack();
}
}
-------------------RandomAccessFile随机d文g---------------
import java.io.*;
public class RandomRead
{
final static String FILENAME="E:\\a.txt";
protected String fileName;
protected RandomAccessFile seeker;
public static void main(String[] argv) throws IOException {
RandomRead r = new RandomRead(FILENAME);
System.out.println("Offset is " + r.readOffset());
System.out.println("Message is \"" + r.readMessage() + "\".");
}
/** Constructor: save filename, construct RandomAccessFile */
public RandomRead(String fname) throws IOException {
fileName = fname;
seeker = new RandomAccessFile(fname, "rw");
}
/** Read the Offset field, defined to be at location 0 in the file. */
public int readOffset() throws IOException {
seeker.seek(0);
seeker.writeChars(FILENAME); // move to very beginning
return seeker.readInt(); // and read the offset
}
/** Read the message at the given offset */
public String readMessage() throws IOException {
seeker.seek(120); // move to where
return seeker.readLine(); // and read the String
}
}
写得很辛?我本来不惛_说什么了,但本着Ҏ术负责的_q是说出?
对于I/O的理解属?U水q?如果java IO有十U的?
错误太多.
对于I/O层次不熟?br />
java IO主要包括
java.io包和java.nio?
java.io主要从四个接口g?
字节:
InputStream/OutputStream,其下为封?qo,特定对象处理的具体实现类.
字符:
Reader/Writer(原文中连Writer接口全都写成Write,以说明Ҏ不了解这了接?如果你经怋用Writer接口怎么会连Writer和Write都分不清,不是一处失?而是全部都是Write)
以上四个接口?底层全部是操作字节的d方式?
java.nio主要以块操作?Buffer)Z,通过可以讑֮的阻塞和非阴塞模?极大地提q了数据输出?br />
入的性能,而且Channel通过选选择器模式的控制,可以实现在同一输出输入通道上多用户q发q行数据传输?比如一个Socket端口可以同时被无限多(理论上不受限?个客Lq发讉K.是l典的I/O多\复用技?
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import
java.io.File;
import
java.io.FileInputStream;
import
java.io.FileNotFoundException;
import
java.io.IOException;
import
java.nio.ByteBuffer;
import
java.nio.channels.FileChannel;
public
class
ReadAString
{
/** */
/**
*
@param
args
*/
public
static
void
main(String[] args)
{
//
TODO 自动生成Ҏ存根
File aFile
=
new
File(
"
d:/test.txt
"
); FileInputStream inFile
=
null
;
try
{ inFile
=
new
FileInputStream(aFile); }
catch
(FileNotFoundException e)
{ e.printStackTrace(System.err); System.exit(
1
); }
FileChannel inChannel
=
inFile.getChannel(); ByteBuffer buf
=
ByteBuffer.allocate(
48
);
//
String buf = "";
try
{
while
(inChannel.read(buf)
!=
-
1
)
{ System.out.println(
"
String read:
"
+
((ByteBuffer)(buf.flip())).asCharBuffer().toString()); buf.clear(); }
System.out.println(
"
EOF readched.
"
); inFile.close(); }
catch
(IOException e)
{ e.printStackTrace(System.err); System.exit(
1
); }
System.exit(
0
); }
}
]]>