Java IO system(輸入輸出系統）

Java1.0中所有與輸入有關的類都繼承自InputStream，此類包含用於讀取單個字節或字節數組的read（）方法。所有與輸出有關的類都繼承自OutputStream，這個類包含用於寫入單個字節或字節數組的write（）方法。

1. InputStream類型

字節數組：ByteArrayInputStream， 內存緩衝區作爲InputStream使用

String對象：StringBufferInputStream， 將一個String轉化成InputStream的一個String，採用一個StringBuffer作爲數據源

文件：FileInputStream，從文件中讀取信息，將File或者FileDescriptor作爲數據源

管道：PipedInputStream，爲相關的PipedOutputStream提供數據源

連接：SequenceInputStream，將多個InputStream對象轉化成單個InputStream使用

過濾器：FilterInputStream，過濾InputStream的數據源

2. OutputStream類型

衍生自這個類的類決定我們的輸入去往何處

字節數組：ByteArrayOutputStream，內存中的緩衝區

文件：FileOutputStream，輸出到文件

管道：PipedOutputStream，自動成爲相關PipedInputStream的輸出

過濾器：FilterOutputStream，過濾OutputStream的輸出

3. FilterInputStream

FilterInputStream用於完成兩類事情：讀取不同的基本類型數據及String對象（DataInputStream），修改InputStream內部行爲如是否進行緩衝

DataInputStream：與DataOutputStream聯合使用，讀取一個流中的基本數據類型

BufferedInputStream：預先讀入緩衝，加快讀取速度

LineNumberInputStream：跟蹤輸入流中的行號

PushbackInputStream：有一個字節的後推緩衝，可後推讀入的上一個字符

4. FilterOutputStream

DataOutputStream：與DataInputStream配合使用，將基本數據類型寫入OutputStream，使得任何機器上的DataInputStream都能正常讀取

PrintStream：用於產生格式化輸出

BufferedOutputStream：要求先寫入緩衝區

5. RandomAccessFile

RandomAccessFile用於包含了已知長度記錄的文件，我們可用seek（）從一條記錄移動至另一條，讀取或修改記錄。RandomAccessFile不屬於InputStream OutputStream系統，而是直接繼承自Object。

6. IO流的典型應用

package com.test;

import java.io.*;

public class IOTest {
	public static void main(String[] args) {
		try {
			//Buffered input file
			DataInputStream in = new DataInputStream(
					new FileInputStream(args[0]));
			String s, s2 = new String();
			while ((s = in.readLine()) != null) {
				s2 += s + "/n";
			}
			in.close();
			
			//Input from memory
			StringBufferInputStream in2 = new StringBufferInputStream(s2);
			
			int c;
			while ((c = in2.read()) != -1) {
				System.out.print((char)c);
			}
			
			//Formatted memory input
			try {
				DataInputStream in3 = new DataInputStream(
						new StringBufferInputStream(s2));
				while (true) {
					System.out.print((char)in3.readByte());
				}
			} catch (EOFException e) {
				System.out.println("End of stream");
			}
			
			//Line numbering & file output
			try {
				LineNumberInputStream li = new LineNumberInputStream(
						new StringBufferInputStream(s2));
				DataInputStream in4 = new DataInputStream(li);
				
				PrintStream out1 = new PrintStream(
						new BufferedOutputStream(
								new FileOutputStream("IODemo.out")));
				while ((s = in4.readLine()) != null) {
					out1.println("Line " + li.getLineNumber() + s);
				}
				out1.close();
			} catch (EOFException e) {
				System.out.println("End of Stream");
			}
			
			//Storing and recovering data
			try {
				DataOutputStream out2 = new DataOutputStream(
						new BufferedOutputStream(
								new FileOutputStream("Data.txt")));
				out2.writeBytes("Here's the value of pi: \n");
				out2.writeDouble(3.141592);
				out2.close();
				DataInputStream in5 = new DataInputStream(
						new BufferedInputStream(
								new FileInputStream("Data.txt")));
				System.out.println(in5.readLine());
				System.out.println(in5.readDouble());
			} catch (EOFException e) {
				System.out.println("End of stream");
			}
			
			//Reading/writing radom access file
			RandomAccessFile rf = new RandomAccessFile("rtest.dat", "rw");
			for (int i = 0; i < 10; i++) {
				rf.writeDouble(i*1.414);
			}
			rf.close();
			
			rf = new RandomAccessFile("rtest.dat", "rw");
			rf.seek(5*8);
			rf.writeDouble(47.0001);;
			rf.close();
			
			rf = new RandomAccessFile("rtest.dat", "r");
			for (int i = 0; i < 10; i ++) {
				System.out.println("Value " + i + ": " + rf.readDouble());
			}
			rf.close();
			
		} catch (FileNotFoundException e) {
			System.out.println("File not found:" + args[0]);
		} catch (IOException e) {
			System.out.println("IO Exception");
		}
	}
}

Java1.1 IO System

Java1.1保留了原來的InputStream和OutputStream系統，但是引入了新的Reader和Writer類實現了另一中IO設計方案。這兩種系統可通過橋類轉換，InputStreamReader將InputStream轉換成Reader，OutputStreamWriter將OutputStream轉換成Writer。新IO系統中添加了與之前對應的類，如下：

Java1.0	Java1.1
InputStream	Reader converter：InputStreamReader
OutputStream	Writer converter：OutputStreamWriter
FileInputStream	FileReader
FileOutputStream	FileWriter
StringBufferInputStream	StringReader
沒有對應類	StringWriter
ByteArrayInputStream	CharArrayReader
ByteArrayOutputStream	CharArrayWriter
PipedyInputStream	PipedReader
PipedyOutputStream	PipedWriter

過濾器：

Java1.0	Java1.1
FilterInputStream	FilterReader
FilterOutputStream	FilterWriter
BufferedInputStream	BufferedReader 含有readline（）
BufferedOutputStream	BufferedWriter
DataInputStream	DataInputStream 用到readline()時需要BufferedReader
PrintStream	PrintWriter
LineNumberInputStream	LineNumberReader
StreamTokenizer	StreamTokenizer
PushBackInputStream	PushBackReader

爲改變的類：

DataOutputStream

File

RandomAccessFile

SequenceInputStream