android按行读取文件内容的几个方法

布满荆棘的人生 2021-10-19 08:58 476阅读 0赞

**一、简单版**

1 import java.io.FileInputStream;
     2 void readFileOnLine(){
     3     String strFileName = "Filename.txt";
     4     FileInputStream fis = openFileInput(strFileName);
     5     StringBuffer sBuffer = new StringBuffer();
     6     DataInputStream dataIO = new DataInputStream(fis);
     7     String strLine = null;
     8     while((strLine =  dataIO.readLine()) != null) {
     9         sBuffer.append(strLine + “\n");
    10     }
    11     dataIO.close();
    12     fis.close();
    13 }

**二、简洁版**

public static String ReadTxtFile(String strFilePath)
        {
                String path = strFilePath;
                String content = "";     //文件内容字符串
                File file = new File(path);    //打开文件
                
                if (file.isDirectory())    //如果path是传递过来的参数，可以做一个非目录的判断
                {
                    Log.d("TestFile", "The File doesn't not exist.");
                }
                else
                {
                    try {
                        InputStream instream = new FileInputStream(file); 
                        if (instream != null) 
                        {
                            InputStreamReader inputreader = new InputStreamReader(instream);
                            BufferedReader buffreader = new BufferedReader(inputreader);
                            String line;
                            //分行读取
                            while (( line = buffreader.readLine()) != null) {
                                content += line + "\n";
                            }                
                            instream.close();
                        }
                    }
                    catch (java.io.FileNotFoundException e) 
                    {
                        Log.d("TestFile", "The File doesn't not exist.");
                    } 
                    catch (IOException e) 
                    {
                         Log.d("TestFile", e.getMessage());
                    }
                }
                return content;
        }

**三、用于长时间使用的apk，并且有规律性的数据**

1，逐行读取文件内容

1 //首先定义一个数据类型，用于保存读取文件的内容 
     2 class WeightRecord {
     3         String timestamp;
     4         float weight;
     5         public WeightRecord(String timestamp, float weight) {
     6             this.timestamp = timestamp;
     7             this.weight = weight;
     8             
     9         }
    10     }
    11     
    12 //开始读取
    13  private WeightRecord[] readLog() throws Exception {
    14         ArrayList<WeightRecord> result = new ArrayList<WeightRecord>();
    15         File root = Environment.getExternalStorageDirectory();
    16         if (root == null)
    17             throw new Exception("external storage dir not found");
    18         //首先找到文件
    19         File weightLogFile = new File(root,WeightService.LOGFILEPATH);
    20         if (!weightLogFile.exists())
    21             throw new Exception("logfile '"+weightLogFile+"' not found");
    22         if (!weightLogFile.canRead())
    23             throw new Exception("logfile '"+weightLogFile+"' not readable");
    24         long modtime = weightLogFile.lastModified();
    25         if (modtime == lastRecordFileModtime)
    26             return lastLog;
    27         // file exists, is readable, and is recently modified -- reread it.
    28         lastRecordFileModtime = modtime;
    29         // 然后将文件转化成字节流读取
    30         FileReader reader = new FileReader(weightLogFile);
    31         BufferedReader in = new BufferedReader(reader);
    32         long currentTime = -1;
    33         //逐行读取
    34         String line = in.readLine();
    35         while (line != null) {
    36             WeightRecord rec = parseLine(line);
    37             if (rec == null)
    38                 Log.e(TAG, "could not parse line: '"+line+"'");
    39             else if (Long.parseLong(rec.timestamp) < currentTime)
    40                 Log.e(TAG, "ignoring '"+line+"' since it's older than prev log line");
    41             else {
    42                 Log.i(TAG,"line="+rec);
    43                 result.add(rec);
    44                 currentTime = Long.parseLong(rec.timestamp);
    45             }
    46             line = in.readLine();
    47         }
    48         in.close();
    49         lastLog = (WeightRecord[]) result.toArray(new WeightRecord[result.size()]);
    50         return lastLog;
    51     }
    52     //解析每一行
    53     private WeightRecord parseLine(String line) {
    54         if (line == null)
    55             return null;
    56         String[] split = line.split("[;]");
    57         if (split.length < 2)
    58             return null;
    59         if (split[0].equals("Date"))
    60             return null;
    61         try {
    62             String timestamp =(split[0]);
    63             float weight =  Float.parseFloat(split[1]) ;
    64             return new WeightRecord(timestamp,weight);
    65         }
    66         catch (Exception e) {
    67             Log.e(TAG,"Invalid format in line '"+line+"'");
    68             return null;
    69         }
    70     }

2，保存为文件

1 public boolean logWeight(Intent batteryChangeIntent) {
     2             Log.i(TAG, "logBattery");
     3             if (batteryChangeIntent == null)
     4                 return false;
     5             try {
     6                 FileWriter out = null;
     7                 if (mWeightLogFile != null) {
     8                     try {
     9                         out = new FileWriter(mWeightLogFile, true);
    10                     }
    11                     catch (Exception e) {}
    12                 }
    13                 if (out == null) {
    14                     File root = Environment.getExternalStorageDirectory();
    15                     if (root == null)
    16                         throw new Exception("external storage dir not found");
    17                     mWeightLogFile = new File(root,WeightService.LOGFILEPATH);
    18                     boolean fileExists = mWeightLogFile.exists();
    19                     if (!fileExists) {
    20                         if(!mWeightLogFile.getParentFile().mkdirs()){
    21                             Toast.makeText(this, "create file failed", Toast.LENGTH_SHORT).show();
    22                         }
    23                         mWeightLogFile.createNewFile();
    24                     }
    25                     if (!mWeightLogFile.exists()) {
    26                         Log.i(TAG, "out = null");
    27                         throw new Exception("creation of file '"+mWeightLogFile.toString()+"' failed");
    28                     }
    29                     if (!mWeightLogFile.canWrite()) 
    30                         throw new Exception("file '"+mWeightLogFile.toString()+"' is not writable");
    31                     out = new FileWriter(mWeightLogFile, true);
    32                     if (!fileExists) {
    33                         String header = createHeadLine();
    34                         out.write(header);
    35                         out.write('\n');
    36                     }
    37                 }
    38                 Log.i(TAG, "out != null");
    39                 String extras = createBatteryInfoLine(batteryChangeIntent);
    40                 out.write(extras);
    41                 out.write('\n');
    42                 out.flush();
    43                 out.close();
    44                 return true;
    45             } catch (Exception e) {
    46                 Log.e(TAG,e.getMessage(),e);
    47                 return false;
    48             }
    49         }

转载于:https://www.cnblogs.com/maoIT/p/4190082.html