java 读文件的几种方式

java中多种方式读文件

本文整合了引用到的一篇文章和自己总结的几个文件操作的点。

1、按字节读取文件内容

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) {}}}}

2、按字符读取文件内容

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<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) {}}}}

3、按行读取文件内容

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) {}}}}

4、随机读取文件内容

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bytereadwhile ((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) {}}}}

//附

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);}}

三、写入文件

Properties init = new Properties();Properties lazy = new Properties();File file = new File(a.properties);FileOutputStream os;try {os = new FileOutputStream(file);init.store(os, "priority loading... ");lazy.store(os, "other lazy loading... ");os.close();} catch (IOException e) {e.printStackTrace();}

四、从properties文件读取

private Properties load() {Properties init = new Properties();try {InputStream is = new FileInputStream(new File(Constants.RESOURCE_BASE+ "a/b.properties"));init.load(is);is.close();} catch (Exception e) {e.printStackTrace();}return init;}