java读写文件大全(字节流读取得方法)
2015-12-11 18:37
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原文地址:http://blog.sina.com.cn/s/blog_6a4af8630101et2t.html
使用Java操作文本文件的方法详解 摘要: 最初java是不支持对文本文件的处理的,为了弥补这个缺憾而引入了Reader和Writer两个类 最初java是不支持对文本文件的处理的,为了弥补这个缺憾而引入了Reader和Writer两个类,这两个类都是抽象类,Writer中 write(char[] ch,int off,int length),flush()和close()方法为抽象方法,Reader中read(char[] ch,int off,int length)和close()方法是抽象方法。子类应该分别实现他们。 当我们读写文本文件的时候,采用Reader是非常方便的,比如FileReader,InputStreamReader和BufferedReader。其中最重要的类是InputStreamReader, 它是字节转换为字符的桥梁。你可以在构造器重指定编码的方式,如果不指定的话将采用底层操作系统的默认编码方式,例如GBK等。当使用FileReader读取文件 的时候。 Java代码 复制代码 收藏代码 view plaincopy to clipboardprint? FileReader fr = new FileReader("ming.txt"); int ch = 0; while((ch = fr.read())!=-1 ) { System.out.print((char)ch); } FileReader fr = new FileReader("ming.txt"); int ch = 0; while((ch = fr.read())!=-1 ) { System.out.print((char)ch); } 其中read()方法返回的是读取得下个字符。当然你也可以使用read(char[] ch,int off,int length)这和处理二进制文件的时候类似,不多说了。如果使用 InputStreamReader来读取文件的时候 while((ch = isr.read())!=-1) { System.out.print((char)ch); } 这和FileReader并没有什么区别,事实上在FileReader中的方法都是从InputStreamReader中继承过来的。read()方法是比较好费时间的,如果为了提高效率 我们可以使用BufferedReader对Reader进行包装,这样可以提高读取得速度,我们可以一行一行的读取文本,使用readLine()方法。 Java代码 复制代码 收藏代码 BufferedReader br = new BufferedReader(new InputStreamReader(new FileInputStream("ming.txt"))); String data = null; while((data = br.readLine())!=null) { System.out.println(data); } 当你明白了如何用Reader来读取文本文件的时候那么用Writer写文件同样非常简单。有一点需要注意,当你写文件的时候,为了提高效率,写入的数据会先 放入缓冲区,然后写入文件。因此有时候你需要主动调用flush()方法。与上面对应的写文件的方法为: Java代码 复制代码 收藏代码 view plaincopy to clipboardprint? ·········10········20········30········40········50········60········70········80········90········100·······110·······120·······130·······140·······150 FileWriter fw = new FileWriter("hello.txt"); String s = "hello world"; fw.write(s,0,s.length()); fw.flush(); OutputStreamWriter osw = new OutputStreamWriter(new FileOutputStream("hello2.txt")); osw.write(s,0,s.length()); osw.flush(); PrintWriter pw = new PrintWriter(new OutputStreamWriter(new FileOutputStream("hello3.txt")),true); pw.println(s); FileWriter fw = new FileWriter("hello.txt"); String s = "hello world"; fw.write(s,0,s.length()); fw.flush(); OutputStreamWriter osw = new OutputStreamWriter(new FileOutputStream("hello2.txt")); osw.write(s,0,s.length()); osw.flush(); PrintWriter pw = new PrintWriter(new OutputStreamWriter(new FileOutputStream("hello3.txt")),true); pw.println(s); 不要忘记用完后关闭流!下面是个小例子,帮助新手理解。其实有的时候java的IO系统是需要我们多记记的,不然哪天就生疏了。 Java代码 复制代码 收藏代码 view plaincopy to clipboardprint? ·········10········20········30········40········50········60········70········80········90········100·······110·······120·······130·······140·······150 import java.io.*; public class TestFile2 { public static void main(String[] args) throws IOException { FileReader fr = new FileReader("ming.txt"); char[] buffer = new char[1024]; int ch = 0; while((ch = fr.read())!=-1 ) { System.out.print((char)ch); } InputStreamReader isr = new InputStreamReader(new FileInputStream("ming.txt")); while((ch = isr.read())!=-1) { System.out.print((char)ch); } BufferedReader br = new BufferedReader(new InputStreamReader(new FileInputStream("ming.txt"))); String data = null; while((data = br.readLine())!=null) { System.out.println(data); } FileWriter fw = new FileWriter("hello.txt"); String s = "hello world"; fw.write(s,0,s.length()); fw.flush(); OutputStreamWriter osw = new OutputStreamWriter(new FileOutputStream("hello2.txt")); osw.write(s,0,s.length()); osw.flush(); PrintWriter pw = new PrintWriter(new OutputStreamWriter(new FileOutputStream("hello3.txt")),true); pw.println(s); fr.close(); isr.close(); br.close(); fw.close(); osw.close(); pw.close(); } } import java.io.*; public class TestFile2 { public static void main(String[] args) throws IOException { FileReader fr = new FileReader("ming.txt"); char[] buffer = new char[1024]; int ch = 0; while((ch = fr.read())!=-1 ) { System.out.print((char)ch); } InputStreamReader isr = new InputStreamReader(new FileInputStream("ming.txt")); while((ch = isr.read())!=-1) { System.out.print((char)ch); } BufferedReader br = new BufferedReader(new InputStreamReader(new FileInputStream("ming.txt"))); String data = null; while((data = br.readLine())!=null) { System.out.println(data); } FileWriter fw = new FileWriter("hello.txt"); String s = "hello world"; fw.write(s,0,s.length()); fw.flush(); OutputStreamWriter osw = new OutputStreamWriter(new FileOutputStream("hello2.txt")); osw.write(s,0,s.length()); osw.flush(); PrintWriter pw = new PrintWriter(new OutputStreamWriter(new FileOutputStream("hello3.txt")),true); pw.println(s); fr.close(); isr.close(); br.close(); fw.close(); osw.close(); pw.close(); } } java中多种方式读文件 一、多种方式读文件内容。 1、按字节读取文件内容 2、按字符读取文件内容 3、按行读取文件内容 4、随机读取文件内容 view plaincopy to clipboardprint? ·········10········20········30········40········50········60········70········80········90········100·······110·······120·······130·······140·······150 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 ReadFromFile { public static void readFileByBytes(String fileName){ File file = new File(fileName); InputStream in = null; try { System.out.println("以字节为单位读取文件内容,一次读一个字节:"); // 一次读一个字节 in = new FileInputStream(file); int tempbyte; while((tempbyte=in.read()) != -1){ System.out.write(tempbyte); } in.close(); } catch (IOException e) { e.printStackTrace(); return; } try { System.out.println("以字节为单位读取文件内容,一次读多个字节:"); //一次读多个字节 byte[] tempbytes = new byte[100]; int byteread = 0; in = new FileInputStream(fileName); ReadFromFile.showAvailableBytes(in); //读入多个字节到字节数组中,byteread为一次读入的字节数 while ((byteread = in.read(tempbytes)) != -1){ System.out.write(tempbytes, 0, byteread); } } catch (Exception e1) { e1.printStackTrace(); } finally { if (in != null){ try { in.close(); } catch (IOException e1) { } } } } public static void readFileByChars(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,一次读一个字节:"); // 一次读一个字符 reader = new InputStreamReader(new FileInputStream(file)); int tempchar; while ((tempchar = reader.read()) != -1){ //对于windows下,rn这两个字符在一起时,表示一个换行。 //但如果这两个字符分开显示时,会换两次行。 //因此,屏蔽掉r,或者屏蔽n。否则,将会多出很多空行。 if (((char)tempchar) != 'r'){ System.out.print((char)tempchar); } } 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:"); //一次读多个字符 char[] tempchars = new char[30]; int charread = 0; reader = new InputStreamReader(new FileInputStream(fileName)); //读入多个字符到字符数组中,charread为一次读取字符数 while ((charread = reader.read(tempchars))!=-1){ //同样屏蔽掉r不显示 if ((charread == tempchars.length)&&(tempchars[tempchars.length-1] != 'r')){ System.out.print(tempchars); }else{ for (int i=0; i<charread; i++){ if(tempchars[i] == 'r'){ continue; }else{ System.out.print(tempchars[i]); } } } } } catch (Exception e1) { e1.printStackTrace(); }finally { if (reader != null){ try { reader.close(); } catch (IOException e1) { } } } } public static void readFileByLines(String fileName){ File file = new File(fileName); BufferedReader reader = null; try { System.out.println("以行为单位读取文件内容,一次读一整行:"); reader = new BufferedReader(new FileReader(file)); String tempString = null; int line = 1; //一次读入一行,直到读入null为文件结束 while ((tempString = reader.readLine()) != null){ //显示行号 System.out.println("line " + line + ": " + tempString); line++; } reader.close(); } catch (IOException e) { e.printStackTrace(); } finally { if (reader != null){ try { reader.close(); } catch (IOException e1) { } } } } public static void readFileByRandomAccess(String fileName){ RandomAccessFile randomFile = null; try { System.out.println("随机读取一段文件内容:"); // 打开一个随机访问文件流,按只读方式 randomFile = new RandomAccessFile(fileName, "r"); // 文件长度,字节数 long fileLength = randomFile.length(); // 读文件的起始位置 int beginIndex = (fileLength > 4) ? 4 : 0; //将读文件的开始位置移到beginIndex位置。 randomFile.seek(beginIndex); byte[] bytes = new byte[10]; int byteread = 0; //一次读10个字节,如果文件内容不足10个字节,则读剩下的字节。 //将一次读取的字节数赋给byteread 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 e1) { } } } } 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 = "C:/temp/newTemp.txt"; ReadFromFile.readFileByBytes(fileName); ReadFromFile.readFileByChars(fileName); ReadFromFile.readFileByLines(fileName); ReadFromFile.readFileByRandomAccess(fileName); } } 二、将内容追加到文件尾部 import java.io.FileWriter; import java.io.IOException; import java.io.RandomAccessFile; public class AppendToFile { public static void appendMethodA(String fileName, String content){ try { // 打开一个随机访问文件流,按读写方式 RandomAccessFile randomFile = new RandomAccessFile(fileName, "rw"); // 文件长度,字节数 long fileLength = randomFile.length(); //将写文件指针移到文件尾。 randomFile.seek(fileLength); randomFile.writeBytes(content); randomFile.close(); } catch (IOException e){ e.printStackTrace(); } } public static void appendMethodB(String fileName, String content){ try { //打开一个写文件器,构造函数中的第二个参数true表示以追加形式写文件 FileWriter writer = new FileWriter(fileName, true); writer.write(content); writer.close(); } catch (IOException e) { e.printStackTrace(); } } public static void main(String[] args) { String fileName = "C:/temp/newTemp.txt"; String content = "new append!"; //按方法A追加文件 AppendToFile.appendMethodA(fileName, content); AppendToFile.appendMethodA(fileName, "append end. n"); //显示文件内容 ReadFromFile.readFileByLines(fileName); //按方法B追加文件 AppendToFile.appendMethodB(fileName, content); AppendToFile.appendMethodB(fileName, "append end. n"); //显示文件内容 ReadFromFile.readFileByLines(fileName); } }
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