JAvaでは様々な方法でファイルを読みます
7046 ワード
JAvaでは、複数の方法でファイルを1、複数の方法でファイルの内容を読みます.1、ファイルの内容をバイトで読み取る2、ファイルの内容を文字で読み取る3、ファイルの内容を行で読み取る4、ファイルの内容をランダムに読み取る
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 {
/**
* , , 、 、 。
* @param fileName
*/
public static void readFileByBytes(String fileName){
File file = new File(fileName);
InputStream in = null;
try {
System.out.println(" , :");
//
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(" , :");
//
byte[] tempbytes = new byte[100];
int byteread = 0;
in = new FileInputStream(fileName);
ReadFromFile.showAvailableBytes(in);
// ,byteread
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) {
}
}
}
}
/**
* , ,
* @param fileName
*/
public static void readFileByChars(String fileName){
File file = new File(fileName);
Reader reader = null;
try {
System.out.println(" , :");
//
reader = new InputStreamReader(new FileInputStream(file));
int tempchar;
while ((tempchar = reader.read()) != -1){
// windows ,rn , 。
// , 。
// , r, n。 , 。
if (((char)tempchar) != 'r'){
System.out.print((char)tempchar);
}
}
reader.close();
} catch (Exception e) {
e.printStackTrace();
}
try {
System.out.println(" , :");
//
char[] tempchars = new char[30];
int charread = 0;
reader = new InputStreamReader(new FileInputStream(fileName));
// ,charread
while ((charread = reader.read(tempchars))!=-1){
// r
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) {
}
}
}
}
/**
* ,
* @param fileName
*/
public static void readFileByLines(String fileName){
File file = new File(fileName);
BufferedReader reader = null;
try {
System.out.println(" , :");
reader = new BufferedReader(new FileReader(file));
String tempString = null;
int line = 1;
// , null
while ((tempString = reader.readLine()) != null){
//
System.out.println("line " + line + ": " + tempString);
line++;
}
reader.close();
} catch (IOException e) {
e.printStackTrace();
} finally {
if (reader != null){
try {
reader.close();
} catch (IOException e1) {
}
}
}
}
/**
*
* @param fileName
*/
public static void readFileByRandomAccess(String fileName){
RandomAccessFile randomFile = null;
try {
System.out.println(" :");
// ,
randomFile = new RandomAccessFile(fileName, "r");
// ,
long fileLength = randomFile.length();
//
int beginIndex = (fileLength > 4) ? 4 : 0;
// beginIndex 。
randomFile.seek(beginIndex);
byte[] bytes = new byte[10];
int byteread = 0;
// 10 , 10 , 。
// 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) {
}
}
}
}
/**
*
* @param in
*/
private static void showAvailableBytes(InputStream in){
try {
System.out.println(" :" + 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);
}
}
、
import java.io.FileWriter;
import java.io.IOException;
import java.io.RandomAccessFile;
/**
*
*/
public class AppendToFile {
/**
* A : RandomAccessFile
* @param fileName
* @param content
*/
public static void appendMethodA(String fileName,
String content){
try {
// ,
RandomAccessFile randomFile = new RandomAccessFile(fileName, "rw");
// ,
long fileLength = randomFile.length();
// 。
randomFile.seek(fileLength);
randomFile.writeBytes(content);
randomFile.close();
} catch (IOException e){
e.printStackTrace();
}
}
/**
* B : FileWriter
* @param fileName
* @param content
*/
public static void appendMethodB(String fileName, String content){
try {
// , true
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!";
// A
AppendToFile.appendMethodA(fileName, content);
AppendToFile.appendMethodA(fileName, "append end. n");
//
ReadFromFile.readFileByLines(fileName);
// B
AppendToFile.appendMethodB(fileName, content);
AppendToFile.appendMethodB(fileName, "append end. n");
//
ReadFromFile.readFileByLines(fileName);
}
}