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。
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FileReader fr = new FileReader("ming.txt");
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int ch = 0;
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while((ch = fr.read())!=-1 )
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{
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System.out.print((char)ch);
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}
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。
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：
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FileWriter fw = new FileWriter("hello.txt");
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String s = "hello world";
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fw.write(s,0,s.length());
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fw.flush();
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OutputStreamWriter osw = new OutputStreamWriter(new FileOutputStream("hello2.txt"));
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osw.write(s,0,s.length());
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osw.flush();
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PrintWriter pw = new PrintWriter(new OutputStreamWriter(new FileOutputStream("hello3.txt")),true);
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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。
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import java.io.*;
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public class TestFile2
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{
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public static void main(String[] args) throws IOException
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{
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FileReader fr = new FileReader("ming.txt");
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char[] buffer = new char[1024];
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int ch = 0;
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while((ch = fr.read())!=-1 )
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{
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System.out.print((char)ch);
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}
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InputStreamReader isr = new InputStreamReader(new FileInputStream("ming.txt"));
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while((ch = isr.read())!=-1)
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{
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System.out.print((char)ch);
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}
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BufferedReader br = new BufferedReader(new InputStreamReader(new FileInputStream("ming.txt")));
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String data = null;
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while((data = br.readLine())!=null)
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{
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System.out.println(data);
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}
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FileWriter fw = new FileWriter("hello.txt");
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String s = "hello world";
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fw.write(s,0,s.length());
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fw.flush();
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OutputStreamWriter osw = new OutputStreamWriter(new FileOutputStream("hello2.txt"));
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osw.write(s,0,s.length());
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osw.flush();
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PrintWriter pw = new PrintWriter(new OutputStreamWriter(new FileOutputStream("hello3.txt")),true);
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pw.println(s);
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fr.close();
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isr.close();
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br.close();
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fw.close();
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osw.close();
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pw.close();
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}
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}
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
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import java.io.BufferedReader;
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import java.io.File;
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import java.io.FileInputStream;
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import java.io.FileReader;
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import java.io.IOException;
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import java.io.InputStream;
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import java.io.InputStreamReader;
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import java.io.RandomAccessFile;
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import java.io.Reader;
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public class ReadFromFile {
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public static void readFileByBytes(String fileName){
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File file = new File(fileName);
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InputStream in = null;
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try {
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System.out.println("以字节为单位读取文件内容，一次读一个字节：");
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in = new FileInputStream(file);
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int tempbyte;
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while((tempbyte=in.read()) != -1){
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System.out.write(tempbyte);
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}
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in.close();
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} catch (IOException e) {
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e.printStackTrace();
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return;
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}
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try {
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System.out.println("以字节为单位读取文件内容，一次读多个字节：");
-
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byte[] tempbytes = new byte[100];
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int byteread = 0;
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in = new FileInputStream(fileName);
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ReadFromFile.showAvailableBytes(in);
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while ((byteread = in.read(tempbytes)) != -1){
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System.out.write(tempbytes, 0, byteread);
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}
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} catch (Exception e1) {
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e1.printStackTrace();
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} finally {
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if (in != null){
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try {
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in.close();
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} catch (IOException e1) {
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}
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}
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}
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}
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public static void readFileByChars(String fileName){
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File file = new File(fileName);
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Reader reader = null;
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try {
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System.out.println("以字符为单位读取文件内容，一次读一个字节：");
-
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reader = new InputStreamReader(new FileInputStream(file));
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int tempchar;
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while ((tempchar = reader.read()) != -1){
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-
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if (((char)tempchar) != 'r'){
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System.out.print((char)tempchar);
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}
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}
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reader.close();
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} catch (Exception e) {
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e.printStackTrace();
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}
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try {
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System.out.println("以字符为单位读取文件内容，一次读多个字节：");
-
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char[] tempchars = new char[30];
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int charread = 0;
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reader = new InputStreamReader(new FileInputStream(fileName));
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while ((charread = reader.read(tempchars))!=-1){
-
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if ((charread == tempchars.length)&&(tempchars[tempchars.length-1] != 'r')){
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System.out.print(tempchars);
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}else{
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for (int i=0; i<charread; i++){
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if(tempchars[i] == 'r'){
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continue;
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}else{
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System.out.print(tempchars[i]);
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}
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}
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}
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}
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} catch (Exception e1) {
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e1.printStackTrace();
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}finally {
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if (reader != null){
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try {
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reader.close();
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} catch (IOException e1) {
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}
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}
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}
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}
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public static void readFileByLines(String fileName){
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File file = new File(fileName);
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BufferedReader reader = null;
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try {
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System.out.println("以行为单位读取文件内容，一次读一整行：");
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reader = new BufferedReader(new FileReader(file));
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String tempString = null;
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int line = 1;
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while ((tempString = reader.readLine()) != null){
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System.out.println("line " + line + ": " + tempString);
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line++;
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}
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reader.close();
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} catch (IOException e) {
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e.printStackTrace();
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} finally {
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if (reader != null){
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try {
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reader.close();
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} catch (IOException e1) {
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}
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}
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}
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}
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public static void readFileByRandomAccess(String fileName){
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RandomAccessFile randomFile = null;
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try {
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System.out.println("随机读取一段文件内容：");
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randomFile = new RandomAccessFile(fileName, "r");
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long fileLength = randomFile.length();
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int beginIndex = (fileLength > 4) ? 4 : 0;
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randomFile.seek(beginIndex);
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byte[] bytes = new byte[10];
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int byteread = 0;
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-
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while ((byteread = randomFile.read(bytes)) != -1){
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System.out.write(bytes, 0, byteread);
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}
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} catch (IOException e){
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e.printStackTrace();
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} finally {
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if (randomFile != null){
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try {
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randomFile.close();
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} catch (IOException e1) {
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}
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}
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}
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}
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private static void showAvailableBytes(InputStream in){
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try {
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System.out.println("当前字节输入流中的字节数为:" + in.available());
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} catch (IOException e) {
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e.printStackTrace();
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}
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}
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public static void main(String[] args) {
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String fileName = "C:/temp/newTemp.txt";
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ReadFromFile.readFileByBytes(fileName);
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ReadFromFile.readFileByChars(fileName);
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ReadFromFile.readFileByLines(fileName);
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ReadFromFile.readFileByRandomAccess(fileName);
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}
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}
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二、将内容追加到文件尾部
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import java.io.FileWriter;
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import java.io.IOException;
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import java.io.RandomAccessFile;
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public class AppendToFile {
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-
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public static void appendMethodA(String fileName,
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String content){
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try {
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RandomAccessFile randomFile = new RandomAccessFile(fileName, "rw");
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long fileLength = randomFile.length();
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randomFile.seek(fileLength);
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randomFile.writeBytes(content);
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randomFile.close();
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} catch (IOException e){
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e.printStackTrace();
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}
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}
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public static void appendMethodB(String fileName, String content){
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try {
-
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FileWriter writer = new FileWriter(fileName, true);
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writer.write(content);
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writer.close();
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} catch (IOException e) {
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e.printStackTrace();
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}
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}
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public static void main(String[] args) {
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String fileName = "C:/temp/newTemp.txt";
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String content = "new append!";
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AppendToFile.appendMethodA(fileName, content);
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AppendToFile.appendMethodA(fileName, "append end. n");
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ReadFromFile.readFileByLines(fileName);
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AppendToFile.appendMethodB(fileName, content);
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AppendToFile.appendMethodB(fileName, "append end. n");
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ReadFromFile.readFileByLines(fileName);
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}
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}
