ファイル入出力 http://www.atmarkit.co.jp/ait/articles/1112/20/news131_3.html

fileIO.java

//リソースを確保した順と逆順に確実にfinallyでリソースを解放する
try {
  String path = "";
  BufferdReader br = null;
  try {
    File file = new File(path);
    String encode = "UTF-8";
    // br = new BufferdReader(new FileReader(file));
    br = new BufferdReader(new InputStreamReader(new FileInputStream(file), encode));
  
    String outPath = file.getAbsolutePath() + ".out";
    BuffertWriter bw = null;
    try {
      //bw = new BufferdWriter(outpath);
      bw = new BufferdWriter(new OutputStreamWriter(new FileOutputStream(outpath),encode));
    
      String line;
      while ((line = br.readLine() != null) {
        bw.write(line);
        bw.newLine();
      }
      bw.flush();
    } finally {
      if (bw != null) {
        bw.close();
      }
    }
  } finally {
    if (br != null) {
      br.close();
    }
  }
} catch (Exception e) {
  e.printStackTrace();
}

fileIO_B.java

//変数へ全部のデータを一時的に保存してから、書き込みをする
try {
  String path = "";
  BufferdReader br = null;
  List lines = new LinkedList();
  String outPath;
  try {
    File file = new File(path);
    br = new BufferdReader(new FileReader(file));
  
    outPath = file.getAbsolutePath() + ".out";
    String line;
    while ((line = br.readLine() != null) {
      lines.add(line);
    }
  } finally {
    if (br != null) {
      br.close();
    }
  }

  BuffertWriter bw = null;
  try {
    bw = new BufferdWriter(outpath)
    for (String outLine : lines) {
      bw.write(outLine);
      bw.newLine();
    }
    bw.flush();
  } finally {
    if (bw != null) {
      bw.close();
    }
  }
} catch (Exception e) {
  e.printStackTrace();
}

fileIO_PrintWriter.java

//リソースを確保した順と逆順に確実にfinallyでリソースを解放する
//PrintWriterはIOExceptionを発生しない
//PrintWriterは自動flushできるが、明示的にflushを呼び出したほうが効率がよい。
try {
  String path = "";
  BufferdReader br = null;
  try {
    File file = new File(path);
    String encode = "UTF-8";
    br = new BufferdReader(new InputStreamReader(new FileInputStream(file), encode));
  
    String outPath = file.getAbsolutePath() + ".out";
    PrintWriter pw = null;
    pw = newPrintWriter(new BufferdWriter(new OutputStreamWriter(new FileOutputStream(outpath), encode)));
    
    String line;
    while ((line = br.readLine() != null) {
      pw.println(line);
    }
    pw.flush();
    pw.close();
  } finally {
    if (br != null) {
      br.close();
    }
  }
} catch (Exception e) {
  e.printStackTrace();
}

fileIO_simple.java

// 例外処理省略版
try {
  String path = "";
  File file = new File(path);
  BufferdReader br = new BufferdReader(new FileReader(file));
  // BufferdReader br = new BufferdReader(new InputStreamReader(new FileInputStream(file), encode));

  String outPath = file.getAbsolutePath() + ".out";
  BuffertWriter bw = new BufferdWriter(outpath)
  //BuffertWriter bw = new BufferdWriter(new OutputStreamWriter(new FileOutputStream(outpath),encode));
  
  String line;
  while ((line = br.readLine() != null) {
    bw.write(line);
    bw.newLine();
  }
  bw.flush();
  bw.close();
  br.close();
} catch (Exception e) {
  e.printStackTrace();
}