android randomaccess 在应用中如何运用

RandomAccessFile 是 Android 中提供的一个类，它允许你在文件的任意位置读取或写入数据。这个类在处理大文件时非常有用，因为它不需要一次性将整个文件加载到内存中。你可以在应用中使用 RandomAccessFile 来实现以下功能：

1. 读取文件的一部分：

import java.io.File;
    
import java.io.IOException;
    
import java.io.RandomAccessFile;


public class MainActivity extends AppCompatActivity {


    @Override
    protected void onCreate(Bundle savedInstanceState) {
    
        super.onCreate(savedInstanceState);
    
        setContentView(R.layout.activity_main);
    

        File file = new File("path/to/your/file.txt");

        try {
    
            RandomAccessFile randomAccessFile = new RandomAccessFile(file, "r");
    
            long fileSize = randomAccessFile.length();
    
            int bufferSize = 1024;
    
            byte[] buffer = new byte[bufferSize];
    
            int bytesRead;
    

            // 从文件的指定位置开始读取
            long position = 50;
    
            randomAccessFile.seek(position);


            while ((bytesRead = randomAccessFile.read(buffer)) != -1) {
    
                // 处理读取到的数据
                String data = new String(buffer, 0, bytesRead);
    
                System.out.println(data);

            }
    

            randomAccessFile.close();

        }
 catch (IOException e) {
    
            e.printStackTrace();

        }

    }

}
    

1. 写入文件的一部分：

import java.io.File;
    
import java.io.IOException;
    
import java.io.RandomAccessFile;


public class MainActivity extends AppCompatActivity {


    @Override
    protected void onCreate(Bundle savedInstanceState) {
    
        super.onCreate(savedInstanceState);
    
        setContentView(R.layout.activity_main);
    

        File file = new File("path/to/your/file.txt");

        try {
    
            RandomAccessFile randomAccessFile = new RandomAccessFile(file, "rw");
    
            long fileSize = randomAccessFile.length();
    
            int bufferSize = 1024;
    
            byte[] buffer = new byte[bufferSize];
    
            int bytesRead;
    

            // 从文件的指定位置开始写入
            long position = 50;
    
            randomAccessFile.seek(position);
    

            String dataToWrite = "This is a new line of text.";
    
            byte[] dataBytes = dataToWrite.getBytes();
    

            randomAccessFile.write(dataBytes);
    
            randomAccessFile.close();

        }
 catch (IOException e) {
    
            e.printStackTrace();

        }

    }

}
    

1. 更新文件的一部分：

import java.io.File;
    
import java.io.IOException;
    
import java.io.RandomAccessFile;


public class MainActivity extends AppCompatActivity {


    @Override
    protected void onCreate(Bundle savedInstanceState) {
    
        super.onCreate(savedInstanceState);
    
        setContentView(R.layout.activity_main);
    

        File file = new File("path/to/your/file.txt");

        try {
    
            RandomAccessFile randomAccessFile = new RandomAccessFile(file, "rw");
    
            long fileSize = randomAccessFile.length();
    
            int bufferSize = 1024;
    
            byte[] buffer = new byte[bufferSize];
    
            int bytesRead;
    

            // 从文件的指定位置开始更新
            long position = 50;
    
            randomAccessFile.seek(position);
    

            String dataToWrite = "This is an updated line of text.";
    
            byte[] dataBytes = dataToWrite.getBytes();
    

            // 将原数据读取到缓冲区
            randomAccessFile.read(buffer);
    

            // 将缓冲区的数据写入到指定位置
            System.arraycopy(dataBytes, 0, buffer, 0, dataBytes.length);
    
            randomAccessFile.write(buffer, 0, dataBytes.length);
    

            randomAccessFile.close();

        }
 catch (IOException e) {
    
            e.printStackTrace();

        }

    }

}
    

1. 删除文件的一部分：

import java.io.File;
    
import java.io.IOException;
    
import java.io.RandomAccessFile;


public class MainActivity extends AppCompatActivity {


    @Override
    protected void onCreate(Bundle savedInstanceState) {
    
        super.onCreate(savedInstanceState);
    
        setContentView(R.layout.activity_main);
    

        File file = new File("path/to/your/file.txt");

        try {
    
            RandomAccessFile randomAccessFile = new RandomAccessFile(file, "rw");
    
            long fileSize = randomAccessFile.length();
    
            int bufferSize = 1024;
    
            byte[] buffer = new byte[bufferSize];
    
            int bytesRead;
    

            // 从文件的指定位置开始删除
            long position = 50;
    
            randomAccessFile.seek(position);
    

            // 将后面的数据写入到当前位置，从而实现删除操作
            String remainingData = readRemainingData(randomAccessFile, position + 10);
    
            randomAccessFile.write(remainingData.getBytes());
    

            randomAccessFile.close();

        }
 catch (IOException e) {
    
            e.printStackTrace();

        }

    }


    private String readRemainingData(RandomAccessFile randomAccessFile, long position) throws IOException {
    
        StringBuilder remainingData = new StringBuilder();
    
        long fileSize = randomAccessFile.length();
    
        int bufferSize = 1024;
    
        byte[] buffer = new byte[bufferSize];
    
        int bytesRead;
    

        randomAccessFile.seek(position);
    

        while (position <
 fileSize) {
    
            bytesRead = randomAccessFile.read(buffer);

            if (bytesRead == -1) {
    
                break;

            }
    
            remainingData.append(new String(buffer, 0, bytesRead));
    
            position += bytesRead;

        }
    

        return remainingData.toString();

    }

}
    

这些示例展示了如何在 Android 应用中使用 RandomAccessFile 来读取、写入、更新和删除文件的一部分。你可以根据自己的需求调整代码以满足你的应用场景。

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