是否可以随机访问存储在 Java 文件中的序列化数组中的特定索引值?

Question

我正在尝试访问序列化数组对象文件中的数组索引位置。我不想反序列化整个数组对象，然后访问数组。我已经能够在C++中使用seekg做到这一点，但在Java中并不成功。

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我尝试使用RandomAccessFile[请参阅以下代码]，但我无法访问数组中的特定位置并将其转换为实际值[请参阅代码注释-//随机访问读取(读取特定位置(]。 让我知道这个问题的解决方案。

法典-

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.RandomAccessFile;
import java.io.Serializable;
import java.util.Arrays;
class Bitmaps implements Serializable
{
int bitmapArray[] = new int[5];
@Override
public String toString() {
return "Bitmaps [bitmapArray=" + Arrays.toString(bitmapArray) + "]";
}
}
public class RandomAccess2 {
public static void main(String[] args) {
try {
Bitmaps bitmaps = new Bitmaps();
String filename = "blocksinfo.txt";
String workingDirectory = System.getProperty("user.dir");
String FILEPATH = workingDirectory + "\" + filename;  //C:\Usersashisworkspacehackerrank1srchackerrank1blocksinfo.txt';
//Initialize array with 100....104
int cnt=100;
for(int i=0;i<5;i++)
bitmaps.bitmapArray[i]=cnt++;

//Serialize array and store in a file
serializeObject(bitmaps, FILEPATH);
int objLength = sizeof(bitmaps);  //function to calculate size of serialized array
System.out.println("Length in bytes after serialization=>"+objLength);

//System.out.println(new String(readFromFile(FILEPATH, 0, ewahBitmap1.sizeInBytes())));
try {
//Random Access Reading (Read all contents)
byte[] byteArray = readFromFile(FILEPATH, 0, objLength);
ByteArrayInputStream in = new ByteArrayInputStream(byteArray);
ObjectInputStream is = new ObjectInputStream(in);
Bitmaps bitmaps2 = (Bitmaps) is.readObject();
System.out.println("Full Random Access Reading=>"+bitmaps2);

//Random Access Reading (Read specific position)
byte[] byteArray1 = readFromFile(FILEPATH, 98, 2);
ByteArrayInputStream in1 = new ByteArrayInputStream(byteArray1);
ObjectInputStream is1 = new ObjectInputStream(in1);
int val = (int) is1.readObject();
System.out.println("Partial Random Access Reading=>"+val);
} catch (ClassNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}

//writeToFile(FILEPATH, ewahBitmap1.toString(), 0);
} catch (IOException e) {
e.printStackTrace();
}
}
private static byte[] readFromFile(String filePath, int position, int size)
throws IOException {
RandomAccessFile file = new RandomAccessFile(filePath, "r");
file.seek(position);
byte[] bytes = new byte[size];
file.read(bytes);
file.close();
return bytes;
}
public static void serializeObject(Object bitmap, String fileName) throws IOException
{
FileOutputStream fos = new FileOutputStream(fileName);
ObjectOutputStream oos = new ObjectOutputStream(fos);
oos.writeObject(bitmap);
oos.close();
}
public static int sizeof(Object obj) throws IOException {
ByteArrayOutputStream byteOutputStream = new ByteArrayOutputStream();
ObjectOutputStream objectOutputStream = new ObjectOutputStream(byteOutputStream);
objectOutputStream.writeObject(obj);
objectOutputStream.flush();
objectOutputStream.close();
return byteOutputStream.toByteArray().length;
}
}

Answer 1

不，这是不可能的。它不是随机访问格式。您必须反序列化数组，然后在内存中对其进行索引。