java中的读文件

package com.demo.ReadFromFile;
/**
* @version
* 多种方式读文件的内容
* 按字节读取文件内容,按字符读取文件的内容,按行读取文件的内容,随即读取文件的内容
*/

import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.RandomAccessFile;
import java.io.Reader;

import com.sun.org.apache.xpath.internal.operations.String;

public class ReadFromFile {
/**
* 以字节为单位读取文件的内容,常用于二进制文件,如声音,图象,影象等文件
* @param filename 文件名
*/
public static void readFileByBytes(java.lang.String filename){
File file=new File(filename);
InputStream in=null;
System.out.println("以字节为单位读取文件的内容,一次读一个字节: ");
//一次读一个字节
try {
in=new FileInputStream(file);
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
int tempbyte;
try {
//不断的读取,直到文件结束
while((tempbyte=in.read())!=-1){
System.out.write(tempbyte);
}
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
try {
in.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
return;
}
System.out.println("以字节为单位读取文件内容,一次读多个字节: ");
//一次读取多个字节
byte[] tempbytes=new byte[100];
int byteread=0;
try {
in=new FileInputStream(filename);
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
ReadFromFile.showAvailabelBytes(in);
try {
while((byteread=in.read(tempbytes))!=-1){
//读取多个字节到数组中,byteead为一次读取的字节数
System.out.write(tempbytes,0,byteread);
}
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
public static void readFileByteChars(java.lang.String filename){
/**
* 以字符为单位读取文件,常用与读文本,数字等类型的文件
*/
File file=new File(filename);
Reader reader=null;
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
try {
reader=new InputStreamReader(new FileInputStream(file));
} catch (FileNotFoundException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
int tempchar;
try {
while((tempchar=reader.read())!=-1){
//在Window下,\r\n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,会换行两次行
//因此,屏蔽掉\r,或者\n;否则,将会多出来很多空行
if(((char)tempchar)!='\r'){
System.out.println((char)tempchar);
}
}
reader.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
System.out.println("以字符为单位读取文件内容,一次读多个字符: ");
char[] tempchars=new char[30];
int charread=0;
try {
reader=new InputStreamReader(new FileInputStream(filename));
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
try {
//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){
if((charread==tempchars.length)&&(tempchars[tempchars.length-1]!='\r')){
System.out.println(tempchars);
}else{
for(int i=0;i<charread;i++){
if(tempchars[i]=='\r'){
continue;
}else{
System.out.print(tempchars[i]);
}
}
}
}
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}finally{
if(reader!=null){
try{
reader.close();
}catch(IOException e){
}
}
}
}
public static void readFileByLines(java.lang.String filename){
File file=new File(filename);
BufferedReader reader=null;
System.out.println("以行为单位读取文件的内容,一次读一整行: ");
try {
reader=new BufferedReader(new FileReader(file));
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
java.lang.String tempString=null;
int line=1;
try {
while((tempString=reader.readLine())!=null){
System.out.println("line "+line+": "+tempString);
line++;
}
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
try {
reader.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}finally{
if(reader!=null){
try {
reader.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}
public static void readFileByRandomAccess(java.lang.String filename){
RandomAccessFile randomFile=null;
System.out.println("随即读取一段文件内容: ");
try {
randomFile=new RandomAccessFile(filename,"r");
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
long fileLength = 0;
try {
fileLength = randomFile.length();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
int beginIndex=(fileLength>4)?4:0;
try {
randomFile.seek(beginIndex);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
byte[] bytes=new byte[10];
int byteread=0;
try {
while((byteread=randomFile.read(bytes))!=-1){
System.out.write(bytes,0,byteread);
}
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}finally{
if(randomFile!=null){
try {
randomFile.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}
private static void showAvailabelBytes(InputStream in){
try {
System.out.println("当前字节输入流中的字节数为: "+in.available());
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
public static void main(java.lang.String args[]){
java.lang.String filename="D:/javap/javanetSource/ReadFromFile/ReadFromFile.txt";
ReadFromFile.readFileByBytes(filename);
ReadFromFile.readFileByteChars(filename);
ReadFromFile.readFileByLines(filename);
ReadFromFile.readFileByRandomAccess(filename);
}

}