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
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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);
}
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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
BufferedReader br = new BufferedReader(new InputStreamReader(new FileInputStream("ming.txt")));
String data = null;
while((data =
br.readLine())!=null)
{
System.out.println(data);
}
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
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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);
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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
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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
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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
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);
}
}