一篇读懂（java中写文件）java files.write，Java读/写文件工具类，java fileinput，

package zmx.util;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 ReadFileUtil {/*** 以字节为单位读取文件，常用于读二进制文件，如图片、声音、影像等文件。*/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);}System.out.println();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[256];int byteread = 0;in = new FileInputStream(fileName);ReadFileUtil.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);}System.out.println();} catch (Exception e1) {e1.printStackTrace();} finally {if (in != null) {try {in.close();} catch (IOException e1) {}}}}/*** 以字符为单位读取文件，常用于读文本，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) {// 对于windows下，\r\n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);}}System.out.println();reader.close();} catch (Exception e) {e.printStackTrace();}try {System.out.println("以字符为单位读取文件内容，一次读多个字符：");// 一次读多个字符char[] tempchars = new char[32];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]);}}}}System.out.println();} catch (Exception e1) {e1.printStackTrace();} finally {if (reader != null) {try {reader.close();} catch (IOException e1) {}}}}/*** 以行为单位读取文件，常用于读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++;}System.out.println();reader.close();} catch (IOException e) {e.printStackTrace();} finally {if (reader != null) {try {reader.close();} catch (IOException e1) {}}}}/*** 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 > 6) ? 6 : 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);}System.out.println();} catch (IOException e) {e.printStackTrace();} finally {if (randomFile != null) {try {randomFile.close();} catch (IOException e1) {}}}}/*** 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 = "D:\\projects\\testWeb\\src\\zmx\\util\\test.txt";ReadFileUtil.readFileByBytes(fileName);ReadFileUtil.readFileByChars(fileName);ReadFileUtil.readFileByLines(fileName);ReadFileUtil.readFileByRandomAccess(fileName);}}

package zmx.util;import java.io.FileWriter;import java.io.IOException;import java.io.RandomAccessFile;public class AppendToFileUtil {/*** A方法追加文件：使用RandomAccessFile*/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();}}/*** B方法追加文件：使用FileWriter*/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 = "D:\\projects\\testWeb\\src\\zmx\\util\\test.txt";String content = "new append!";//按方法A追加文件AppendToFileUtil.appendMethodA(fileName, content);AppendToFileUtil.appendMethodA(fileName, "append end. \n");//显示文件内容ReadFileUtil.readFileByLines(fileName);//按方法B追加文件AppendToFileUtil.appendMethodB(fileName, content);AppendToFileUtil.appendMethodB(fileName, "append end. \n");//显示文件内容ReadFileUtil.readFileByLines(fileName);}}