java使用ByteBuffer记录文件大小并进行多文件合并和拆分

1.背景

2.代码工程

实验目的

 对文件进行二进制流合并和拆分

合并代码

1. ByteBuffer.allocate(4): 创建一个大小为 4 字节的 ByteBuffer，因为 Java 中的整数（int）是 4 个字节。
2. putInt(publicCertsContent.length): 将 publicCertsContent 的字节数组长度（即证书文件的字节长度）存入 ByteBuffer。这样就把证书内容的长度存储为一个 4 字节的整数。
3. array(): 将 ByteBuffer 转换为字节数组。这个数组包含了公钥证书内容长度的 4 字节表示形式。

• 有符号整数（int 类型）：
  • 范围是：-2,147,483,648 到 2,147,483,647
  • 其中 1 位用于符号（正负），31 位用于数值。
• 无符号整数（unsigned int，Java 中没有直接支持，但可以通过转换处理）：
  • 范围是：0 到 4,294,967,295

package com.et;


import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.nio.ByteBuffer;


public class FileMerger {

    public static void main(String[] args) {
        String privateKeys = "D:/IdeaProjects/Java-demo/file/src/main/resources/privateKeys.keystore";
        String publicCerts = "D:/IdeaProjects/Java-demo/file/src/main/resources/publicCerts.keystore";
        merger(privateKeys,publicCerts);

    }
    public static String merger(String privateKeys, String publicCerts) {
        String directoryPath = FileUtils.extractDirectoryPath(privateKeys);
        String mergedFile =directoryPath+"merge.keystore";

        try {
            byte[] privateKeysContent =   FileUtils.readBinaryFile(privateKeys);
            byte[] publicCertsContent =   FileUtils.readBinaryFile(publicCerts);


            // create outputStream
            ByteArrayOutputStream outputStream = new ByteArrayOutputStream();

            // write keystore length（4 byte）
            outputStream.write(ByteBuffer.allocate(4).putInt(privateKeysContent.length).array());

            // write keystore content
            outputStream.write(privateKeysContent);

            // witer license content（4 byte int ）
            outputStream.write(ByteBuffer.allocate(4).putInt(publicCertsContent.length).array());

            // write license content
            outputStream.write(publicCertsContent);

            // write merge content to file
            FileUtils.writeBinaryFile(mergedFile, outputStream.toByteArray());
          
            System.out.println("merge success " + mergedFile);
        } catch (IOException e) {
            e.printStackTrace();
        }
        return mergedFile;
    }



}

拆分代码

outputStream.write(ByteBuffer.allocate(4).putInt(content.length).array());

ByteBuffer buffer = ByteBuffer.wrap(fileContent); // 假设 fileContent 是读取的字节数组
int size = buffer.getInt(); // 读取前 4 个字节，获取文件大小

package com.et;


import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;


public class FileSplitter {

    public static void main(String[] args) {
        String mergedFile = "D:/IdeaProjects/Java-demo/file/src/main/resources/merge.keystore";
        split(mergedFile);

    }
    private static void debugContent(byte[] content, String fileName) {
        System.out.printf("File: %s%n", fileName);
        System.out.printf("Length: %d%n", content.length);
        System.out.print("Content: ");
        for (byte b : content) {
            System.out.printf("%02X ", b);
        }
        System.out.println();
    }
    static String[] split(String mergedFile) {
        String directoryPath = FileUtils.extractDirectoryPath(mergedFile);
        String privateKeysFile = directoryPath + ".privateKeys.keystore";
        String publicCertsFile = directoryPath + ".publicCerts.keystore";
        String[] filePaths = new String[]{privateKeysFile, publicCertsFile};

        try {
            // read merge content
            byte[] mergedContent = FileUtils.readBinaryFile(mergedFile);

            // use ByteBuffer parse
            ByteBuffer buffer = ByteBuffer.wrap(mergedContent);

            // read privateKeys content length
            int privateKeysLength = buffer.getInt();

            // read privateKeys content
            byte[] privateKeysContent = new byte[privateKeysLength];
            buffer.get(privateKeysContent);

            // read publicCerts content length
            int publicCertsLength = buffer.getInt();

            // read publicCerts content
            byte[] publicCertsContent = new byte[publicCertsLength];
            buffer.get(publicCertsContent);

            // write privateKeys and publicCerts content to file
            FileUtils.writeBinaryFile(privateKeysFile, privateKeysContent);
            FileUtils.writeBinaryFile(publicCertsFile, publicCertsContent);

            System.out.println("merge file split " + privateKeysFile + " and " + publicCertsFile);

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

        return filePaths;
    }






    private static byte[] extractContent(byte[] mergedContent, byte[] beginMarker, byte[] endMarker) {
        int beginIndex = indexOf(mergedContent, beginMarker);
        int endIndex = indexOf(mergedContent, endMarker, beginIndex);

        if (beginIndex != -1 && endIndex != -1) {
            // Move past the start marker
            beginIndex += beginMarker.length;

            // Adjust endIndex to exclude the end marker
            int adjustedEndIndex = endIndex;

            // Extract content
            return Arrays.copyOfRange(mergedContent, beginIndex, adjustedEndIndex);
        } else {
            return new byte[0]; // Return empty array if markers are not found
        }
    }


    private static byte[] removeEmptyLines(byte[] content) {
        // Convert byte array to list of lines
        List<byte[]> lines = splitIntoLines(content);

        // Filter out empty lines
        lines = lines.stream()
                .filter(line -> line.length > 0)
                .collect(Collectors.toList());

        // Reassemble content
        return mergeLines(lines);
    }

    private static List<byte[]> splitIntoLines(byte[] content) {
        List<byte[]> lines = new ArrayList<>();
        int start = 0;

        for (int i = 0; i < content.length; i++) {
            if (content[i] == '\n') { // Line break
                lines.add(Arrays.copyOfRange(content, start, i));
                start = i + 1;
            }
        }

        if (start < content.length) {
            lines.add(Arrays.copyOfRange(content, start, content.length));
        }

        return lines;
    }

    private static byte[] mergeLines(List<byte[]> lines) {
        ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
        for (byte[] line : lines) {
            try {
                outputStream.write(line);
                outputStream.write('\n'); // Re-add line break
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return outputStream.toByteArray();
    }

    private static int indexOf(byte[] array, byte[] target) {
        return indexOf(array, target, 0);
    }

    private static int indexOf(byte[] array, byte[] target, int start) {
        for (int i = start; i <= array.length - target.length; i++) {
            if (Arrays.equals(Arrays.copyOfRange(array, i, i + target.length), target)) {
                return i;
            }
        }
        return -1; // Return -1 if target not found
    }






}

工具类

package com.et;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;

public class FileUtils {

    static byte[] readBinaryFile(String filePath) throws IOException {
        File file = new File(filePath);
        try (FileInputStream fis = new FileInputStream(file)) {
            byte[] fileBytes = new byte[(int) file.length()];
            fis.read(fileBytes);
            return fileBytes;
        }
    }
    public static String extractDirectoryPath(String filePath) {
        File file = new File(filePath);
        return file.getParent()+File.separator; // 获取文件所在的目录
    }
     static void writeBinaryFile(String filePath, byte[] content) throws IOException {
        try (FileOutputStream fos = new FileOutputStream(filePath)) {
            fos.write(content);
        }
    }
}

以上只是一些关键代码，所有代码请参见下面代码仓库

代码仓库

• https://github.com/Harries/Java-demo(file)

3.测试

package com.et;

public class Main {
    public static void main(String[] args) {
        System.out.println("Hello world!");
        String privateKeys = "D:/IdeaProjects/Java-demo/file/src/main/resources/privateKeys.keystore";
        String publicCerts = "D:/IdeaProjects/Java-demo/file/src/main/resources/publicCerts.keystore";
        FileMerger.merger(privateKeys,publicCerts);
        String mergedFile = "D:/IdeaProjects/Java-demo/file/src/main/resources/merge.keystore";
        FileSplitter.split(mergedFile);
    }
}

merge success D:\IdeaProjects\Java-demo\file\src\main\resources\merge.keystore
merge file split D:\IdeaProjects\Java-demo\file\src\main\resources\.privateKeys.keystore and D:\IdeaProjects\Java-demo\file\src\main\resources\.publicCerts.keystore

4.引用

•  http://www.liuhaihua.cn/archives/711411.html