如何使用Java读文件和写文件代码讲解

import java.io.BufferedReader; import java.io.File; import java.io.FileInputStream; import java.io.FileReader; import java.io.IOException; import java.io.InputStream; import java.io.InputStreamReader; import java.io.RandomAccessFile; import java.io.Reader; public class JavaIO { /** * 采用的是操作系统底层默认的编码方式，GBK等，非UTF8 * */ /** * 以字节为单位读取文件内容，常用于读取二进制文件，比如图片、影像、声音等文件 * */ public static void readFileByBytes(String filename) { File file=new File(filename); FileInputStream in=null; try { System.out.println("以字节为单位读取文件,一次读一个字节: "); in=new FileInputStream(file); int temp=0; while ((temp=in.read()) != -1) { System.out.println(temp); } in.close(); } catch (IOException e) { e.printStackTrace(); return ; } try { System.out.println("以字节为单位读取文件，一次读多个字节： "); byte[] temp=new byte[100]; int byteread=0; in=new FileInputStream(file); JavaIO.showAvailableBytes(in); while ((byteread=in.read(temp)) != -1) { System.out.write(temp,0,byteread); } } catch (Exception e1) { e1.printStackTrace(); } finally { if (in != null) { try { in.close(); } catch (IOException e1) { } } } } /** * 以字符为单位读取文件，常用于读文本，数字等类型的文件 * */ public static void readFileByChar(String filename) { File file=new File(filename); Reader reader=null; try { System.out.println("以字符为单位读取文件内容，一次一个字节："); //InputStreamReader类:是字节向字符转换的桥梁 reader=new InputStreamReader(new FileInputStream(file)); int temp; while ((temp=reader.read()) != -1) { if (((char)temp) != '\r') { System.out.println((char)temp); } } reader.close(); } catch (Exception e) { e.printStackTrace(); } try { System.out.println("以字符为单位读取文件内容，一次读多个字节： "); char[] temp=new char[30]; int charread=0; reader=new InputStreamReader(new FileInputStream(filename)); while ((charread=reader.read(temp)) != -1) { if ((charread == temp.length) && (temp[temp.length-1]!='\r')) { System.out.println(temp); } else { for (int i=0; i 4 ? 4 : 0); randomfile.seek(beginIndex); byte[] bytes=new byte[10]; int byteread=0; while ((byteread=randomfile.read(bytes)) != -1) { System.out.write(bytes,0,byteread); } } catch (IOException e) { e.printStackTrace(); } finally { if (randomfile != null) { try { randomfile.close(); } catch (IOException e) { } } } } private static void showAvailableBytes(InputStream in) { try { System.out.println("当前字节输入流中的字节数为：" + in.available()); } catch (IOException e) { e.printStackTrace(); } } public static void main(String[] args) { String filename="E:\\BaiYiShaoNian.txt"; JavaIO.readFileByBytes(filename); JavaIO.readFileByChar(filename); JavaIO.readFileByLine(filename); JavaIO.readFileByRandomAccess(filename); } }

import java.io.BufferedWriter; import java.io.File; import java.io.FileNotFoundException; import java.io.FileOutputStream; import java.io.FileWriter; import java.io.IOException; import java.io.OutputStreamWriter; public class JavaIO2 { public static void main(String[] args) throws IOException { String Path="E:\\天才白痴梦\\JAVA"; File file=new File("E:\\天才白痴梦\\JAVA","BaiYiShaoNian.txt"); if (!file.exists()) { try { file.createNewFile(); } catch (IOException e) { e.printStackTrace(); } } /** * Java写入文件的三种方法 * */ FileOutputStream fos=null; BufferedWriter bw=null; FileWriter fw=null; int value=1000; try { fos=new FileOutputStream(new File(Path+"fos.txt")); long begin=System.currentTimeMillis(); for (int i=1; i<=value; i++) { fos.write(5); } long end=System.currentTimeMillis(); System.out.println("TheCostTime of FileOutputStream is : " + (end-begin)); fos.close(); bw=new BufferedWriter(new OutputStreamWriter(new FileOutputStream(new File(Path+"br.txt")),"UTF8")); begin=System.currentTimeMillis(); for (int i=1; i<=value; i++) { bw.write(5); bw.newLine(); } bw.close(); end=System.currentTimeMillis(); System.out.println("TheCostTime of BufferedWriter is : " + (end-begin)); fw=new FileWriter(Path+"fw.txt"); begin=System.currentTimeMillis(); for (int i=1; i<=value; i++) { fw.write(5); } fw.close(); end=System.currentTimeMillis(); System.out.println("TheCostTime of FileWriter is : " + (end-begin)); } catch (Exception e) { // TODO Auto-generated catch block e.printStackTrace(); } finally { try { fos.close(); //FileOutputStream bw.close(); //BufferedWriter fw.close(); //FileWriter } catch (Exception e) { e.printStackTrace(); } } } }