| package book.io;
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;
/**
*多种方式读取文件
*按字节读取文件内容、按字符读取文件内容、按行读取文件内容、随机读取文件内容
*/
public class ReadFromFile {
//以字节为单位读取文件，常用于读取二进制文件，如图片、声音、视频等文件
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，一次读取一个字节：");
//一次读取一个字节
in = new FileInputStream(file);
int tempbyte;
//不断读取，知道文件结束
while((tempbyte=in.read()) != -1){
System.out.write(tempbyte);
}
in.close();
}catch (Exception 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);
//将多个字节读入到字节数组中，byteread为一次读入的字节数
while((byteread = in.read(tempbytes)) != -1){
System.out.write(tempbytes,0,byteread);
}
} catch (Exception e) {
e.printStackTrace();
}finally{
if(in != null){
try {
in.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
//以字符为单位读取文件，常用于读取文本、数字等类型的文件
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，一次读一个字符：");
//一次读一个字符
reader = new InputStreamReader(new FileInputStream(file));
int tempchar;
while((tempchar = reader.read()) != -1){
if(((char)tempchar)!='\r'){
System.out.println((char)tempchar);
}
}
} catch (Exception e) {
e.printStackTrace();
}
try {
System.out.println("以字符为单位读取文件内容，一次读多个字符：");
char[] tempchars = new char[30];
int charread = 0;
reader = new InputStreamReader(new FileInputStream(fileName));
//将多个字符读取到字符数组中，charread为一次读取的字符数
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.println(tempchars[i]);
}
}
}
}
} catch (Exception e) {
e.printStackTrace();
}
}
//以行为单位读取文件，常用于读取面向行的格式化文件
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;
//一次读一行，直到读到null，读取文件结束
while((tempString = reader.readLine()) != null){
System.out.println("line "+ line + ":" + tempString);
line++;
}
reader.close();
} catch (Exception e) {
e.printStackTrace();
}finally{
if(reader != null){
try {
reader.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
//随机读取文件
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");
long fileLength = randomFile.length();
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
while((byteread = randomFile.read(bytes)) != -1){
System.out.write(bytes, 0, byteread);
}
} catch (Exception e) {
e.printStackTrace();
}finally{
if(randomFile != null){
try {
randomFile.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
//显示输入流中还剩的字节数
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:/Users/Admin/Desktop/CAI/20160718/newTemp.txt";
ReadFromFile.readFileByBytes(fileName);
ReadFromFile.readFileByChars(fileName);
ReadFromFile.readFileByLines(fileName);
ReadFromFile.readFileByRandomAccess(fileName);
}
}
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