編寫一個已存在的文件

如何編寫一個存在於FileOutputStream的文件？當我運行該程序兩次，第二次oos和fos是空編寫一個已存在的文件

public class ReadFile { 
    static FileOutputStream fos = null; 
    static ObjectOutputStream oos = null; 
    public static void main(String[] args) throws IOException, ClassNotFoundException { 

     File f = new File("file.tmp"); 
     if (f.exists()) { 
      //How to retreive an old oos to can write on old file ? 
      oos.writeObject("12345"); 
      oos.writeObject("Today"); 
     } 
     else 
     { 
      fos = new FileOutputStream("file.tmp"); 
      oos = new ObjectOutputStream(fos); 
     } 
     oos.close(); 
    } 
}

來源

2012-11-05 Mehdi

ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream(f,true));

如果要追加到文件

來源

2012-11-05 13:01:48 thedayofcondor

ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream(f, true));

在代碼中，你有ObjectOutputStream oos = null;，所以oos是null。你需要初始化它。就像這樣：

public class ReadFile { 
    static FileOutputStream fos = null; 
    static ObjectOutputStream oos = null; 
    public static void main(String[] args) throws IOException, ClassNotFoundException { 

     File f = new File("file.tmp"); 
     oos = new ObjectOutputStream(new FileOutputStream(f, true)); 
     if (f.exists()) { 
      //How to retreive an old oos to can write on old file ? 
      oos.writeObject("12345"); 
      oos.writeObject("Today"); 
     } 
     else 
     { 
      fos = new FileOutputStream(f, true); 
      oos = new ObjectOutputStream(fos); 
     } 
     oos.close(); 
    } 
}

來源

2012-11-05 13:00:44 Doorknob

如果你不想overrite文件，真正的參數添加到文件或文件的OutputStream構造

new FileOutputStream(new File("Filename.txt"), true); 

Parameters: 
name - the system-dependent file name 
append - if true, then bytes will be written to the end of the file rather than the beginning

來源

2012-11-05 13:01:05 Mob

如果您打算編寫純文本，請嘗試使用FileWriter而不是FileOutputStream。

PrintWriter out = new PrintWriter(new BufferedWriter(new FileWriter("outfilename", true))); 
    out.println("the text");

第二個參數（true）會告訴附加到文件。

來源

2012-11-05 13:01:59

只是設置爲true

FileOutputStream d = new FileOutputStream(file, append);

第二個參數創建新 FileOutputStream

來源

2012-11-05 13:02:43

編寫一個已存在的文件

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