Question

I have a Java program which searches for a folder with the date of yesterday and compresses it to a 7zip file and deletes it at the end. Now I have noticed that the generated 7zip archive files by my program are way too big. When I use a program like 7-Zip File Manager to compress my files it generates an archive which is 5 kb big while my program generates an archive which is 737 kb big for the same files (which have a 873 kb size). Now I am afraid that my program does not compress it to a 7zip file but do a usual zip file. Is there a way to change something in my code so that it generates a smaller 7zip file like 7-Zip File Manager would do it?

package SevenZip;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.concurrent.TimeUnit;

import org.apache.commons.compress.archivers.sevenz.SevenZArchiveEntry;
import org.apache.commons.compress.archivers.sevenz.SevenZOutputFile;

public class SevenZipUtils {

    public static void main(String[] args) throws InterruptedException, IOException {

        String sourceFolder = "C:/Users/Ferid/Documents/Dates/";
        String outputZipFile = "/Users/Ferid/Documents/Dates";
        int sleepTime = 0;
        compress(sleepTime, outputZipFile, sourceFolder);
    }

    public static boolean deleteDirectory(File directory, int sleepTime) throws InterruptedException {
        if (directory.exists()) {
            File[] files = directory.listFiles();
            if (null != files) {
                for (int i = 0; i < files.length; i++) {
                    if (files[i].isDirectory()) {
                        deleteDirectory(files[i], sleepTime);
                        System.out.println("Folder deleted: " + files[i]);
                    } else {
                        files[i].delete();
                        System.out.println("File deleted: " + files[i]);
                    }
                }
            }
        }
        TimeUnit.SECONDS.sleep(sleepTime);
        return (directory.delete());
    }

    public static void compress(int sleepTime, String outputZipFile, String sourceFolder)
            throws IOException, InterruptedException {

        // finds folder of yesterdays date
        final Calendar cal = Calendar.getInstance();
        cal.add(Calendar.DATE, -1); // date of yesterday
        String timeStamp = new SimpleDateFormat("yyyyMMdd").format(cal.getTime()); // format the date
        System.out.println("Yesterday was " + timeStamp);

        if (sourceFolder.endsWith("/")) { // add yesterday folder to sourcefolder path
            sourceFolder = sourceFolder + timeStamp;
        } else {
            sourceFolder = sourceFolder + "/" + timeStamp;
        }

        if (outputZipFile.endsWith("/")) { // add yesterday folder name to outputZipFile path
            outputZipFile = outputZipFile + " " + timeStamp + ".7z";
        } else {
            outputZipFile = outputZipFile + "/" + timeStamp + ".7z";
        }

        File file = new File(sourceFolder);

        if (file.exists()) {
            try (SevenZOutputFile out = new SevenZOutputFile(new File(outputZipFile))) {
                addToArchiveCompression(out, file, ".");
                System.out.println("Files sucessfully compressed");

                deleteDirectory(new File(sourceFolder), sleepTime);
            }
        } else {
            System.out.println("Folder does not exist");
        }
    }

    private static void addToArchiveCompression(SevenZOutputFile out, File file, String dir) throws IOException {
        String name = dir + File.separator + file.getName();
        if (file.isFile()) {
            SevenZArchiveEntry entry = out.createArchiveEntry(file, name);
            out.putArchiveEntry(entry);

            FileInputStream in = new FileInputStream(file);
            byte[] b = new byte[1024];
            int count = 0;
            while ((count = in.read(b)) > 0) {
                out.write(b, 0, count);
            }
            out.closeArchiveEntry();
            in.close();
            System.out.println("File added: " + file.getName());
        } else if (file.isDirectory()) {
            File[] children = file.listFiles();
            if (children != null) {
                for (File child : children) {
                    addToArchiveCompression(out, child, name);
                }
            }
            System.out.println("Directory added: " + file.getName());
        } else {
            System.out.println(file.getName() + " is not supported");
        }
    }
}

I am using the Apache Commons Compress library

EDIT: Here is a link where I have some of the Apache Commons Compress code from.

Answer 1

Common Compress在容器文件中为每个存档条目启动一个新块。注意此处的块计数器：

不是您想要的答案，但是文档说它不支持“实体压缩”-将多个文件写入一个块。参见文档here中的第5段。

快速浏览一下，发现了其他一些支持LZMA压缩的Java库，但是在7-Zip的父容器文件格式中，我找不到能做到这一点的库。也许其他人知道替代方案...

听起来像是普通的zip文件格式（例如，通过ZipOutputStream）是不是一种选择？

Answer 2

~~我没有足够的代表发表评论，所以~~这是我的想法：

我看不到您在哪里设置压缩率，因此SevenZOutputFile可能没有使用（或非常低）压缩。正如@CristiFati所说，压缩的差异很奇怪，尤其是对于文本文件
正如@ df778899所指出的那样，不支持实体压缩，这是实现最佳压缩率的方式，因此您将无法像7z命令行那样出色

也就是说，如果确实不能使用zip，那么您最后的选择就是使用call the proper command line directly within your program。

如果不是必须使用纯7z，则另一种选择是使用类似“ tgz”的格式来模拟实体压缩：首先将所有文件压缩为非压缩文件（例如tar格式或不压缩的zip文件），然后然后使用标准Java Deflate算法以zip模式压缩单个文件。当然，只有在使用该格式的其他进程识别出该格式后，这种方法才可行。

Answer 3

改为使用7-Zip file archiver，它将832 KB文件轻松压缩为26.0 KB：

获取其Jar和SDK。
选择LZMA压缩.java相关文件。
在项目属性中添加Run自变量：e "D:\\2017ASP.pdf" "D:\\2017ASP.7z"，e代表encode，"input path" "output path"。
运行项目[LzmaAlone.java]。

结果

案例1（.pdf文件）：从33,969 KB到24,645 KB。

案例2（.docx文件）：从832 KB到26.0 KB。

Java 7zip compression is too big

3 个答案: