[转载]读取文件方法大全
[list]
[*]1、按字节读取文件内容
[*]2、按字符读取文件内容
[*]3、按行读取文件内容
[*]4、随机读取文件内容
[/list]
[code="java"]
public class ReadFromFile {
??? /**
???? * 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);
??????????? }
??????????? 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) {
??????????????? }
??????????? }
??????? }
??? }
??? /**
???? * 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，\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);
??????????????? }
??????????? }
??????????? 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) {
??????????????? }
??????????? }
??????? }
??? }
??? /**
???? * 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++;
??????????? }
??????????? 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 > 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) {
??????????????? }
??????????? }
??????? }
??? }
??? /**
???? * 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 = "C:/temp/newTemp.txt";
??????? ReadFromFile.readFileByBytes(fileName);
??????? ReadFromFile.readFileByChars(fileName);
??????? ReadFromFile.readFileByLines(fileName);
??????? ReadFromFile.readFileByRandomAccess(fileName);
??? }
}
// 将内容追加到文件尾部
public class AppendToFile {
??? /**
???? * 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 = "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);
??? }
}[/code]
转载自[url]http://www.cnblogs.com/lovebread/archive/2009/11/23/1609122.html[/url]
[code="java"]
/**
???? * 以行为单位读取文件，常用于读面向行的格式化文件
???? */?
??? public static List<String> readFileByLines(String fileName) {?
??? ?List<String> rules = new ArrayList<String>();
??????? 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?
??????????? String rule = "";
??????????? while ((tempString = reader.readLine()) != null) {?
??????????????? // 显示行号?
??????????????? // System.out.println("line " + line + ": " + tempString);
???????????????
??????????????? rule += tempString + "\n";
??????????????? if("end".equals(tempString.trim())){
??????????????? ?rules.add(rule);
??????????????? ?rule = "";
??????????????? }
??????????????? line++;?
??????????? }?
??????????? reader.close();?
??????? } catch (IOException e) {?
??????????? e.printStackTrace();?
??????? } finally {?
??????????? if (reader != null) {?
??????????????? try {?
??????????????????? reader.close();?
??????????????? } catch (IOException e1) {?
??????????????? }?
??????????? }?
??????? }?
??????? return rules;
??? }?
public static boolean appendContent(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();
??????????? return false;
??????? }?
??????? return true;
??? }
[/code]
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