1、按字節讀取文件內容
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public class ReadFromFile {public static void readFileByBytes(String fileName) {File file = new File(fileName);InputStream in = null;try {System.out.println("以字節為單位讀取文件內容，一次讀一個字節：");// 一次讀一個字節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("以字節為單位讀取文件內容，一次讀多個字節：");// 一次讀多個字節byte[] tempbytes = new byte[100];int byteread = 0;in = new FileInputStream(fileName);ReadFromFile.showAvailableBytes(in);// 讀入多個字節到字節數組中，byteread為一次讀入的字節數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、按字符讀取文件內容
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public static void readFileByChars(String fileName) {File file = new File(fileName);Reader reader = null;try {System.out.println("以字符為單位讀取文件內容，一次讀一個字節：");// 一次讀一個字符reader = new InputStreamReader(new FileInputStream(file));int tempchar;while ((tempchar = reader.read()) != -1) {// 對于windows下，\r\n這兩個字符在一起時，表示一個換行。// 但如果這兩個字符分開顯示時，會換兩次行。// 因此，屏蔽掉\r，或者屏蔽\n。否則，將會多出很多空行。if (((char) tempchar) != '\r') {System.out.print((char) tempchar);}}reader.close();} catch (Exception e) {e.printStackTrace();}try {System.out.println("以字符為單位讀取文件內容，一次讀多個字節：");// 一次讀多個字符char[] tempchars = new char[30];int charread = 0;reader = new InputStreamReader(new FileInputStream(fileName));// 讀入多個字符到字符數組中，charread為一次讀取字符數while ((charread = reader.read(tempchars)) != -1) {// 同樣屏蔽掉\r不顯示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、按行讀取文件內容
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public static void readFileByLines(String fileName) {File file = new File(fileName);BufferedReader reader = null;try {System.out.println("以行為單位讀取文件內容，一次讀一整行：");reader = new BufferedReader(new FileReader(file));String tempString = null;int line = 1;// 一次讀入一行，直到讀入null為文件結束while ((tempString = reader.readLine()) != null) {// 顯示行號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、隨機讀取文件內容
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public static void readFileByRandomAccess(String fileName) {RandomAccessFile randomFile = null;try {System.out.println("隨機讀取一段文件內容：");// 打開一個隨機訪問文件流，按只讀方式randomFile = new RandomAccessFile(fileName, "r");// 文件長度，字節數long fileLength = randomFile.length();// 讀文件的起始位置int beginIndex = (fileLength > 4) ? 4 : 0;// 將讀文件的開始位置移到beginIndex位置。randomFile.seek(beginIndex);byte[] bytes = new byte[10];int byteread = 0;// 一次讀10個字節，如果文件內容不足10個字節，則讀剩下的字節。// 將一次讀取的字節數賦給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) {}}}}private static void showAvailableBytes(InputStream in) {try {System.out.println("當前字節輸入流中的字節數為:" + 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);}} |
5、將內容追加到文件尾部
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public class AppendToFile {public static void appendMethodA(String fileName, String content) {try {// 打開一個隨機訪問文件流，按讀寫方式RandomAccessFile randomFile = new RandomAccessFile(fileName, "rw");// 文件長度，字節數long fileLength = randomFile.length();//將寫文件指針移到文件尾。randomFile.seek(fileLength);randomFile.writeBytes(content);randomFile.close();} catch (IOException e) {e.printStackTrace();}}public static void appendMethodB(String fileName, String content) {try {//打開一個寫文件器，構造函數中的第二個參數true表示以追加形式寫文件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");//顯示文件內容ReadFromFile.readFileByLines(fileName);//按方法B追加文件AppendToFile.appendMethodB(fileName, content);AppendToFile.appendMethodB(fileName, "append end. \n");//顯示文件內容ReadFromFile.readFileByLines(fileName);}} |
