java--File的读取和写入实例

实例来源think in java

根据需要读取文件返回不同类型的信息进行选择使用。

实例1

使用BufferReader读取。

package io;// 使用Reader方式进行读取 import java.io.*;public class BufferedInputFile {// Throw exceptions to console:public static String read(String filename) throws IOException {// 使用BufferedReader进行缓冲，来提高文件的读取数据BufferedReader in = new BufferedReader(new FileReader(filename));String s;StringBuilder sb = new StringBuilder();while ((s = in.readLine()) != null)sb.append(s + "\n");in.close();return sb.toString();}public static void main(String[] args) throws IOException {System.out.print(read("C:\\Users\\zm\\workspace\\Thinking in java\\src\\io\\BufferedInputFile.java"));}}

实例2

使用StringReader类读取，in.read()以int形式返回下一个字节。

package io;// 从内存中读取import java.io.*;public class MemoryInput {public static void main(String[] args) throws IOException {StringReader in = new StringReader(BufferedInputFile.read("C:\\Users\\zm\\workspace\\Thinking in java\\src\\io\\MemoryInput.java"));int c;while ((c = in.read()) != -1)System.out.print((char) c);}}

实例3

使用DataInputStream类读取，in.readByte()返回的byte类型。

package io;//相对TestEOF.java 此方法不能检测字节是否结束//面向字节的IO类import java.io.*;public class FormattedMemoryInput {public static void main(String[] args) throws IOException {try {DataInputStream in = new DataInputStream(new ByteArrayInputStream(BufferedInputFile.read("C:\\Users\\zm\\workspace\\Thinking in java\\src\\io\\FormattedMemoryInput.java").getBytes()));while (true)System.out.print((char) in.readByte());} catch (EOFException e) {System.err.println("End of stream");}}}

另一种用法，差异在第9行，使用in.available() != 0，判断检测字节是否结束。

FormattedMemoryInput例子在运行时 不能检测流中是否还有字节，所以在控制台最后会抛出一个异常：End of stream

下面用法可以避免此问题。

package io;import java.io.*;public class TestEOF {public static void main(String[] args) throws IOException {DataInputStream in = new DataInputStream(new BufferedInputStream(new FileInputStream("C:\\Users\\zm\\workspace\\Thinking in java\\src\\io\\TestEOF.java")));while (in.available() != 0)System.out.print((char) in.readByte());}}

实例1

基本的文件写入

package io;// 基本的文件输出import java.io.*;public class BasicFileOutput {static String file = "C:\\Users\\zm\\workspace\\Thinking in java\\src\\io\\BasicFileOutput.out";public static void main(String[] args) throws IOException {BufferedReader in = new BufferedReader(new StringReader(BufferedInputFile.read("C:\\Users\\zm\\workspace\\Thinking in java\\src\\io\\BasicFileOutput.java")));PrintWriter out = new PrintWriter(new BufferedWriter(new FileWriter(file)));int lineCount = 1;String s;while ((s = in.readLine()) != null)out.println(lineCount++ + ": " + s);out.close();// Show the stored file:System.out.println(BufferedInputFile.read(file));}}

快捷用法，PrintWriter提供了进行缓存操作构造函数，省去了我们自己进行包装。

package io;// 输出方式的快捷用法，PrintWriter提供了进行缓存操作构造函数import java.io.*;public class FileOutputShortcut {static String file = "C:\\Users\\zm\\workspace\\Thinking in java\\src\\io\\FileOutputShortcut.out";public static void main(String[] args) throws IOException {BufferedReader in = new BufferedReader(new StringReader(BufferedInputFile.read("C:\\Users\\zm\\workspace\\Thinking in java\\src\\io\\FileOutputShortcut.java")));// Here's the shortcut:PrintWriter out = new PrintWriter(file);int lineCount = 1;String s;while ((s = in.readLine()) != null)out.println(lineCount++ + ": " + s);out.close();// Show the stored file:System.out.println(BufferedInputFile.read(file));}}

读取和写入工具类

//: net/mindview/util/TextFile.java// Static functions for reading and writing text files as// a single string, and treating a file as an ArrayList.package net.mindview.util;import java.io.*;import java.util.*;public class TextFile extends ArrayList<String> {private static String gpfile = "C:\\Users\\zm\\workspace\\Thinking in java\\src\\net\\mindview\\util\\";// Read a file as a single string:public static String read(String fileName) {StringBuilder sb = new StringBuilder();try {BufferedReader in = new BufferedReader(new FileReader(new File(fileName).getAbsoluteFile()));try {String s;while ((s = in.readLine()) != null) {sb.append(s);sb.append("\n");}} finally {in.close();}} catch (IOException e) {throw new RuntimeException(e);}return sb.toString();}// Write a single file in one method call:public static void write(String fileName, String text) {try {PrintWriter out = new PrintWriter(new File(fileName).getAbsoluteFile());try {out.print(text);} finally {out.close();}} catch (IOException e) {throw new RuntimeException(e);}}// Read a file, split by any regular expression:public TextFile(String fileName, String splitter) {super(Arrays.asList(read(fileName).split(splitter)));// Regular expression split() often leaves an empty// String at the first position:if (get(0).equals(""))remove(0);}// Normally read by lines:public TextFile(String fileName) {this(fileName, "\n");}public void write(String fileName) {try {PrintWriter out = new PrintWriter(new File(fileName).getAbsoluteFile());try {for (String item : this)out.println(item);} finally {out.close();}} catch (IOException e) {throw new RuntimeException(e);}}// Simple test:public static void main(String[] args) {String file = read(gpfile + "TextFile.java");write("d:\\test.txt", file);TextFile text = new TextFile("d:\\test.txt");text.write("d:\\test2.txt");// Break into unique sorted list of words:TreeSet<String> words = new TreeSet<String>(new TextFile(gpfile + "TextFile.java", "\\W+"));// Display the capitalized words:System.out.println(words.headSet("a"));}}