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
//首先定义一个数据类型，用于保存读取文件的内容
class WeightRecord {
String timestamp;
float weight;
public WeightRecord(String timestamp, float weight) {
this.timestamp = timestamp;
this.weight = weight; }
} //开始读取
private WeightRecord[] readLog() throws Exception {
ArrayList<WeightRecord> result = new ArrayList<WeightRecord>();
File root = Environment.getExternalStorageDirectory();
if (root == null)
throw new Exception("external storage dir not found");
//首先找到文件
File weightLogFile = new File(root,WeightService.LOGFILEPATH);
if (!weightLogFile.exists())
throw new Exception("logfile '"+weightLogFile+"' not found");
if (!weightLogFile.canRead())
throw new Exception("logfile '"+weightLogFile+"' not readable");
long modtime = weightLogFile.lastModified();
if (modtime == lastRecordFileModtime)
return lastLog;
// file exists, is readable, and is recently modified -- reread it.
lastRecordFileModtime = modtime;
// 然后将文件转化成字节流读取
FileReader reader = new FileReader(weightLogFile);
BufferedReader in = new BufferedReader(reader);
long currentTime = -1;
//逐行读取
String line = in.readLine();
while (line != null) {
WeightRecord rec = parseLine(line);
if (rec == null)
Log.e(TAG, "could not parse line: '"+line+"'");
else if (Long.parseLong(rec.timestamp) < currentTime)
Log.e(TAG, "ignoring '"+line+"' since it's older than prev log line");
else {
Log.i(TAG,"line="+rec);
result.add(rec);
currentTime = Long.parseLong(rec.timestamp);
}
line = in.readLine();
}
in.close();
lastLog = (WeightRecord[]) result.toArray(new WeightRecord[result.size()]);
return lastLog;
}
//解析每一行
private WeightRecord parseLine(String line) {
if (line == null)
return null;
String[] split = line.split("[;]");
if (split.length < 2)
return null;
if (split[0].equals("Date"))
return null;
try {
String timestamp =(split[0]);
float weight = Float.parseFloat(split[1]) ;
return new WeightRecord(timestamp,weight);
}
catch (Exception e) {
Log.e(TAG,"Invalid format in line '"+line+"'");
return null;
}
}
2，保存为文件
public boolean logWeight(Intent batteryChangeIntent) {
Log.i(TAG, "logBattery");
if (batteryChangeIntent == null)
return false;
try {
FileWriter out = null;
if (mWeightLogFile != null) {
try {
out = new FileWriter(mWeightLogFile, true);
}
catch (Exception e) {}
}
if (out == null) {
File root = Environment.getExternalStorageDirectory();
if (root == null)
throw new Exception("external storage dir not found");
mWeightLogFile = new File(root,WeightService.LOGFILEPATH);
boolean fileExists = mWeightLogFile.exists();
if (!fileExists) {
if(!mWeightLogFile.getParentFile().mkdirs()){
Toast.makeText(this, "create file failed", Toast.LENGTH_SHORT).show();
}
mWeightLogFile.createNewFile();
}
if (!mWeightLogFile.exists()) {
Log.i(TAG, "out = null");
throw new Exception("creation of file '"+mWeightLogFile.toString()+"' failed");
}
if (!mWeightLogFile.canWrite())
throw new Exception("file '"+mWeightLogFile.toString()+"' is not writable");
out = new FileWriter(mWeightLogFile, true);
if (!fileExists) {
String header = createHeadLine();
out.write(header);
out.write('\n');
}
}
Log.i(TAG, "out != null");
String extras = createBatteryInfoLine(batteryChangeIntent);
out.write(extras);
out.write('\n');
out.flush();
out.close();
return true;
} catch (Exception e) {
Log.e(TAG,e.getMessage(),e);
return false;
}
}