java如何生成文件，写文件，关闭文件，能否给出完整代码

Question

写文件
-----------------------------------------------------------------------    
try {
      DataOutputStream out2 =
        new DataOutputStream(
          new BufferedOutputStream(
            new FileOutputStream("Data.txt")));
      out2.writeDouble(3.14159);
      out2.writeChars("That was pi\n");
      out2.writeBytes("That was pi\n");
      out2.close();
      DataInputStream in5 =
        new DataInputStream(
          new BufferedInputStream(
            new FileInputStream("Data.txt")));
      BufferedReader in5br =
        new BufferedReader(
          new InputStreamReader(in5));
      // Must use DataInputStream for data:
      System.out.println(in5.readDouble());
      // Can now use the "proper" readLine():
      System.out.println(in5br.readLine());
      // But the line comes out funny.
      // The one created with writeBytes is OK:
      System.out.println(in5br.readLine());
    } catch(EOFException e) {
      System.err.println("End of stream");
    }

Answer 1

读文件
----------------------------------------------------------    
BufferedReader in =
      new BufferedReader(
        new FileReader("IOStreamDemo.java"));
    String s, s2 = new String();
    while((s = in.readLine())!= null)
      s2 += s + "\n";
    in.close();

Answer 2

try {
            System.out.println("===========开始记录日志信息============");
            String newLine = null;
            String filePath = this.sysInfo.logDir + "log/logActionIDLog.log";
            //建立输入流
            File logFile = new File(filePath);
            boolean exits = logFile.createNewFile();
            System.out.println("=========文件已经存在==========" + !exits);
            FileWriter fWriter = new FileWriter(logFile, true);
            PrintWriter out = new PrintWriter(fWriter, true); ;
            if (exits) {
                newLine =
                    "first";
                //写记录，并关闭流
                out.println(newLine);
                //out.close();
                //fWriter.close();
            }
            //组成记录
            newLine = "test"            //写记录，并关闭流
            out.println(newLine);
            out.close();
            fWriter.close();
        }
        catch (FileNotFoundException e) {
            e.printStackTrace();
        }
        catch (IOException ie) {
            ie.printStackTrace();
        }
        System.out.println("========结束记录日志信息=========");