将对象附加到二进制文件

Question

你有以下方法:

public static void writeToBinary(Object obj, String filename) 
{
 ObjectOutputStream oos = null;
 try {
  oos = new ObjectOutputStream(new FileOutputStream(filename));
  oos.writeObject(obj);
 } catch (Exception e) {
  e.printStackTrace();
 }  finally{
  try{
   if (oos != null) oos.close ();
  }catch (Exception e){
   e.printStackTrace();
  }
 }
}

如您所见,该方法将对象写入二进制文件.

但是现在您想要重写相同的方法以允许将对象附加到同一文件.
好的,你看一下java文档,你会发现你必须在FileOutputStream中添加一个值为true的参数:

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

你编译但是,哎呀!似乎它继续覆盖文件.

好吧,问题就开始了.在google中搜索后,您会发现必须使用SAME ObjectOutputStream将对象附加到同一文件中.你希望有一个函数,每次调用它时,它都会追加一个对象.即:

writeToBinary("a", filename);
writeToBinary("b", filename);

但正如我之前所说,你必须使用相同的ObjectOutputStream.

解决方案1:

ObjectOutputStream out = getOutputStream (filename);
writeToBinary("a", out);
writeToBinary("b", out);
writeToBinary("c", out);
out.close ();

这非常难看,因为我想隐藏流的使用.

还有其他解决方案吗？

编辑:该方法是静态的.它位于实用程序类中,其中所有方法都是静态的.

编辑2:解决了!附加到ObjectOutputStream.请参阅我的问题的已接受答案.谢谢.

Answer 1

解决了.

import java.io.EOFException;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.OutputStream;

public class Test{
    private static String filename = "test";

    public static void main(String[] args) {
        writeToBinary (filename, "a", true);
        writeToBinary (filename, "b", true);
        writeToBinary (filename, "c", true);
        readFromBinaryFile (filename);
    }

    public static void writeToBinary (String filename, Object obj, boolean append){
        File file = new File (filename);
        ObjectOutputStream out = null;

        try{
            if (!file.exists () || !append) out = new ObjectOutputStream (new FileOutputStream (filename));
            else out = new AppendableObjectOutputStream (new FileOutputStream (filename, append));
            out.writeObject(obj);
            out.flush ();
        }catch (Exception e){
            e.printStackTrace ();
        }finally{
            try{
                if (out != null) out.close ();
            }catch (Exception e){
                e.printStackTrace ();
            }
        }
    }

    public static void readFromBinaryFile (String filename){
        File file = new File (filename);

        if (file.exists ()){
            ObjectInputStream ois = null;
            try{
                ois = new ObjectInputStream (new FileInputStream (filename));
                while (true){
                    String s = (String)ois.readObject ();
                    System.out.println (s);
                }
            }catch (EOFException e){

            }catch (Exception e){
                e.printStackTrace ();
            }finally{
                try{
                    if (ois != null) ois.close();
                }catch (IOException e){
                    e.printStackTrace ();
                }
            }
        }
    }

    private static class AppendableObjectOutputStream extends ObjectOutputStream {
          public AppendableObjectOutputStream(OutputStream out) throws IOException {
            super(out);
          }

          @Override
          protected void writeStreamHeader() throws IOException {}
    }
}