Java编程思想：I/O的典型使用方式

import java.io.*;
public class Test {
public static void main(String[] args) {
// BufferedInputFile.test();
// MemoryInput.test();
// FormattedMemoryInput.test();
// TestEOF.test1();
// TestEOF.test2();
// BasicFileOutput.test();
// FileOutputShotcut.test();
// StoringAndRecoveringData.test();
UsingRandomAccessFile.test();
}
}
/*
打开一个文件用于字符输入，为提高速度，需要用到缓冲
*/
class BufferedInputFile {
public static String read(String file) {
String result = null;
try {
BufferedReader reader = new BufferedReader(new FileReader(file));
StringBuilder sb = new StringBuilder();
String str;
while ((str=reader.readLine()) != null) {sb.append(str+"\n");
}
reader.close();
result=sb.toString();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
return result;
}
public static void test() {
System.out.println(read("./src/Test.java"));
}
}
/*
BufferedInputFile.read()读入的String结果被用来创造一个StringReader
然后调用read()每次读取一个字符，并将它送到控制台
*/
class MemoryInput {
public static void test() {
StringReader sr = new StringReader(BufferedInputFile.read("./src/Test.java"));
int c;
try {
while ((c = sr.read()) != -1) {System.out.println((char) c);
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
/*
要读取格式化数据，可以使用DataInputStream，它是一个面向字节的I/O类（不是面向
字符的）。因此我们必须使用InputStream类而不是Reader类
*/
class FormattedMemoryInput {
public static void test() {
try{
DataInputStream in = new DataInputStream( new ByteArrayInputStream( BufferedInputFile.read("./src/Test.java").getBytes() )
);
while (true) {System.out.println((char)in.readByte());
}
} catch (IOException e) {
System.out.println("End of stream");
e.printStackTrace();
}
}
}
/*
利用avaliable()来查看还有多少可供读取的字符，用于检测输入是否结束
*/
class TestEOF {
//需要为ByteArrayInputStream提供字节数组作为构造参数
public static void test1() {
try{
DataInputStream in = new DataInputStream( new ByteArrayInputStream( BufferedInputFile.read("./src/Test.java").getBytes() )
);
while (in.available()!=0) {System.out.println((char)in.readByte());
}
} catch (IOException e) {
e.printStackTrace();
}
}
//这儿DataInputStream和BufferedInputStream都是装饰器
public static void test2() {
try {
DataInputStream in = new DataInputStream( new BufferedInputStream( new FileInputStream("./src/Test.java") )
);
} catch (FileNotFoundException e) {
e.printStackTrace();
}
}
}
/*
为了提供格式化机制，FileWriter被装饰成了PrintWriter
*/
class BasicFileOutput {
private static String file = "./src/file3";
public static void test() {
try {
//创建文件输入流
BufferedReader in = new BufferedReader( new StringReader( BufferedInputFile.read("./src/Test.java")));
//创建文件输出流
PrintWriter out = new PrintWriter( new BufferedWriter( new FileWriter(file)));
//从输入流写到输出流
int lineCount=1;
String str;
while ((str = in.readLine()) != null) {out.println(lineCount++ + " : "+str);
}
out.close();
System.out.println(BufferedInputFile.read(file));
} catch (IOException e) {
e.printStackTrace();
}
}
}
/*
PrintWriter的辅助构造器，可以减少装饰工作
*/
class FileOutputShotcut {
private static String file = "./src/file4";
public static void test() {
try {
//创建文件输入流
BufferedReader in = new BufferedReader( new StringReader( BufferedInputFile.read("./src/Test.java")));
//创建文件输出流
PrintWriter out = new PrintWriter(file);
//从输入流写到输出流
int lineCount=1;
String str;
while ((str = in.readLine()) != null) {out.println(lineCount++ + " : "+str);
}
out.close();
System.out.println(BufferedInputFile.read(file));
} catch (IOException e) {
e.printStackTrace();
}
}
}
/*
DataOutputStream输出可供另一个流恢复的数据
*/
class StoringAndRecoveringData {
public static void test() {
try{
//建立输出流，输出数据
DataOutputStream out = new DataOutputStream( new BufferedOutputStream( new FileOutputStream("./src/file4")));
//建立输入流，恢复数据
DataInputStream in = new DataInputStream( new BufferedInputStream( new FileInputStream("./src/file4")));
out.writeDouble(3.1415926);
out.writeUTF("That was pi");
out.writeDouble(1.41413);
out.writeUTF("Square root of 2");
out.close();
System.out.println(in.readDouble());
System.out.println(in.readUTF());
System.out.println(in.readDouble());
System.out.println(in.readUTF());
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
}
/*
RandomAcccessFile拥有读取基本烈性和UTF-8字符串的各种具体的方法，同时seek()
方法可以在文件中到处移动
*/
class UsingRandomAccessFile {
private static String file = "./src/file5";
private static void display(){
try{
RandomAccessFile rf = new RandomAccessFile(file,"r");
for (int i = 0; i <7; i++) {System.out.println("VALUE "+i+": "+rf.readDouble());
}
System.out.println(rf.readUTF());
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
private static void write() {
try{
RandomAccessFile rf = new RandomAccessFile(file,"rw");
for (int i = 0; i <7; i++) {rf.writeDouble(i*1.414);
}
rf.writeUTF("The end of the file");
rf.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
public static void test() {
write();
display();
try{
RandomAccessFile rf = new RandomAccessFile(file,"rw");
rf.seek(5*8);
rf.writeDouble(47.01);
rf.close();
display();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
}

&＃160;