Java 文件读写全攻略+断点续传示例

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 

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);
    }
}

5、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);
    }
}

转载至:http://www.cnblogs.com/lovebread/archive/2009/11/23/1609122.html

 

其中,RandomAccessFile可实现断点续传,RandomAccessFile中的关键方法:seek(int index);即,将内容追加到index之后

贴一段出来吧,因为项目原因不能全贴,但这点够了(okhttp+线程池)

/**
     * 已有下载,断点续传
     */
    private void startDown2(final long progess) {
        mApplication.executorService.execute(new Runnable() {
            @Override
            public void run() {

                final Request request2 = new Request.Builder()
                        .url(url)
                        .build();
                final Call call2 = new OkHttpClient().newCall(request2);

                call2.enqueue(new Callback() {
                    @Override
                    public void onFailure(Request request, IOException e) {

                    }

                    @Override
                    public void onResponse(Response response) throws IOException {
                        sumCount = response.body().contentLength();
                    }
                });


                final Request request = new Request.Builder()
                        .url(url)
                        .addHeader("RANGE", "bytes=" + progess + "-" + sumCount)
                        .build();
                final Call call = new OkHttpClient().newCall(request);
                call.enqueue(new Callback() {
                    @Override
                    public void onFailure(final Request request, final IOException e) {
                        Log.i(TAG, "onFailure: 获取文件失败:" + request.hashCode() + "  " + request.headers());
                    }

                    @Override
                    public void onResponse(Response response) {
                        InputStream is = null;
                        RandomAccessFile raf = null;
                        BufferedInputStream bis = null;
                        byte[] buf = new byte[1024];
                        int len = 0;
                        try {
                            is = response.body().byteStream();
                            File file = new File(DOC_PATH, fileName);
                            raf = new RandomAccessFile(file, "rwd");
                            bis = new BufferedInputStream(is);
                            raf.seek(progess);
                            while ((len = bis.read(buf, 0, 1024)) != -1) {
                                raf.write(buf, 0, len);
                                gress += len;
                                if (linster != null)
                                    linster.DownProgress(fileName, DOC_PATH, progess + gress, sumCount, group, child);
                                if (isPuase) {
                                    gress = 0;
                                    if (linster != null) {
                                        linster.OnPause(fileName, group, child);
                                    }
                                    Log.i(TAG, "onResponse: 1断点收到暂停指令!文件:" + fileName);
                                    break;
                                }
                            }
                            //如果下载文件成功,第一个参数为文件的绝对路径
                        } catch (IOException e) {
                            Log.i(TAG, "onResponse: 断点续传下载出错:" + e);
                        } finally {
                            try {
                                if (is != null) is.close();
                                if (bis != null) bis.close();
                                if (raf != null) raf.close();
                                if (!isPuase) {
                                    Log.i(TAG, "onResponse: 断点续传下载成功");
                                    isOver = true;
                                    handler.post(new Runnable() {
                                        @Override
                                        public void run() {
                                            if (linster != null)
                                                linster.DownSuccess(fileName, DOC_PATH, group, child);
                                        }
                                    });
                                }
                            } catch (IOException e) {
                                Log.i(TAG, "onResponse: 断点续传下载失败");
                            }
                        }
                    }
                });
            }
        });
    }

 

posted @ 2017-08-31 11:47  猴子1  阅读(606)  评论(0编辑  收藏  举报