1、按位元組讀取文件內容
public class ReadFromFile {public static void readFileByBytes(String fileName) {File file = new File(fileName);InputStream in = null;try {System.out.println("以位元組為單位讀取檔案內容，一次讀取一個字節：");// 一次讀一個位元組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("以位元組為單位讀取檔案內容，一次讀取多個位元組：");// 一次讀取多個位元組byte[] tempbytes = new byte[100];int byteread = 0;in = new FileInputStream(fileName);ReadFromFile.showAvailableBytes(in);// 讀入多個位元組到位元組數組中，byteread為一次讀入的位元組數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、按字元讀取文件內容
public static void readFileByChars(String fileName) {File file = new File(fileName);Reader reader = null;try {System.out.println("以字元為單位讀取檔案內容，一次讀取一個位元組："); // 一次讀取一個字元reader = new InputStreamReader(new FileInputStream(file));int tempchar;while ((tempchar = reader.read()) != -1) {// 對於windows下，/r/n這兩個字元在一起時，表示一個換行。 // 但如果這兩個字元分開顯示時，會換兩次行。 // 因此，屏蔽掉/r，或屏蔽/n。否則，將會多出許多空行。 if (((char) tempchar) != '/r') {System.out.print((char) tempchar);}}reader.close();} catch (Exception e) {e.printStackTrace();} try {System.out.println("以字元為單位讀取檔案內容，一次讀取多個位元組：");// 一次讀取多個字元char[] tempchars = new char[30];int charread = 0;reader = new InputStreamReader(new FileInputStream(fileName));// 讀入多個字元到字元陣列中，charread為一次讀取字元數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
public static void readFileByLines(String fileName) {File file = new File(fileName);BufferedReader reader = null;try {System.out.println("以行為單位讀取檔案內容，一次讀取一整行：");reader = new BufferedReader(new FileReader(file));String tempString = null;int line = 1;//一次讀入一行，直到讀入null為檔案結束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
public static void readFileByRandomAccess(String fileName) {RandomAccessFile randomFile = null;try {System.out.println("隨機讀取一段檔案內容：");// 開啟一個隨機存取檔案流，按唯讀方式。 (fileName, "r");// 檔案長度，位元組數長 fileLength = randomFile.length();// 讀取檔案的起始位置int beginIndex = (fileLength > 4) ? 4 : 0;// 將讀取檔案的開始位置移到beginIndex位置。 randomFile.seek(beginIndex);byte[] bytes = new byte[10];int byteread = 0;// 一次讀10個字節，如果檔案內容不足10個字節，則讀剩下的位元組。 // 將一次讀取的位元組數賦給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("目前位元組輸入流中的位元組數為:" + 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
public class AppendToFile {public static void appendMethodA(String fileName, String content) {try {// 開啟一個隨機存取檔案流，以讀取寫入方式RandomAccessFile randomFile = new RandomAccessFile(fileName, "rw");// 檔案長度，字節數長 fileLength = randomFile.length();//將寫入檔案指標移到檔案尾。 randomFile.seek(fileLength);randomFile.writeBytes(content);randomFile.close();} catch (IOException e) {e.printStackTrace();}}public static void appendMethodB(String fileName, String content) {try {/ /開啟一個寫入檔案器，建構函式中的第二個參數true表示以追加形式寫入檔案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追加檔案AppendToFile.appendMethodA(fileName, content);AppendToFile.appendMethodA(fileName, "append end. /n");//顯示檔案內容ReadFromFile.readFileByLines(fileName);//按方法B追加檔AppendToFile.appendMethodB(fileName, content);AppendToFile.appendMethodB(fileName, "append end. /n");//顯示檔案內容ReadFromFile.readFileByLines(fileName);}}