如何使用ZipOutputStream创建压缩的Zip存档，以便ZipEntry的方法getSize（）返回正确的大小？ [英] How to create compressed Zip archive using ZipOutputStream so that method getSize() of ZipEntry returns correct size?
问题描述
考虑将单个文件 test_file.pdf 放入zip存档 test.zip 的代码示例，然后阅读此存档：
Consider the code example that put a single file test_file.pdf into zip archive test.zip and then read this archive:
import java.io.*;
import java.util.zip.ZipEntry;
import java.util.zip.ZipInputStream;
import java.util.zip.ZipOutputStream;
public class Main {
public static void main(String[] args) {
File infile = new File("test_file.pdf");
try (
FileInputStream fis = new FileInputStream(infile);
ZipOutputStream zos = new ZipOutputStream(new FileOutputStream("test.zip"));
) {
int bytesRead;
byte[] buffer = new byte[1024];
ZipEntry entry = new ZipEntry("data");
entry.setSize(infile.length());
zos.putNextEntry(entry);
while ((bytesRead = fis.read(buffer)) >= 0)
{
zos.write(buffer, 0, bytesRead);
}
zos.closeEntry();
} catch (IOException e) {
e.printStackTrace();
}
try (
ZipInputStream zis = new ZipInputStream(new BufferedInputStream(
new FileInputStream(new File("test.zip"))));
) {
ZipEntry entry = zis.getNextEntry();
System.out.println("Entry size: " + entry.getSize());
zis.closeEntry();
} catch (IOException e) {
e.printStackTrace();
}
}
}
输出：
条目大小：-1
但是如果创建未压缩的zip存档（方法
But if create uncompressed zip archive (method ZipEntry.STORED), getSize() returns correct size:
import java.io.*;
import java.util.zip.CRC32;
import java.util.zip.ZipEntry;
import java.util.zip.ZipInputStream;
import java.util.zip.ZipOutputStream;
public class Main {
public static void main(String[] args) {
File infile = new File("test_file.pdf");
try (
FileInputStream fis = new FileInputStream(infile);
ZipOutputStream zos = new ZipOutputStream(new FileOutputStream("test.zip"));
) {
int bytesRead;
byte[] buffer = new byte[1024];
CRC32 crc = new CRC32();
try (
BufferedInputStream bis = new BufferedInputStream(new FileInputStream(infile));
) {
crc.reset();
while ((bytesRead = bis.read(buffer)) != -1) {
crc.update(buffer, 0, bytesRead);
}
}
ZipEntry entry = new ZipEntry("data");
entry.setMethod(ZipEntry.STORED);
entry.setCompressedSize(infile.length());
entry.setSize(infile.length());
entry.setCrc(crc.getValue());
zos.putNextEntry(entry);
while ((bytesRead = fis.read(buffer)) >= 0)
{
zos.write(buffer, 0, bytesRead);
}
zos.closeEntry();
} catch (IOException e) {
e.printStackTrace();
}
try (
ZipInputStream zis = new ZipInputStream(new BufferedInputStream(
new FileInputStream(new File("test.zip"))));
) {
ZipEntry entry = zis.getNextEntry();
System.out.println("Entry size: " + entry.getSize());
zis.closeEntry();
} catch (IOException e) {
e.printStackTrace();
}
}
}
输出（例如但正确）：
条目大小：9223192
Output (for example but correct):
Entry size: 9223192
压缩的zip存档正确 entry.getSize（）存在（例如Ark程序的zip存档）。
Compressed zip archives with correct entry.getSize() exists (e.g. zip archives by Ark program).
所以问题：如何创建压缩（ ZipEntry.DEFLATED 或另一个if exists）zip存档只使用标准库返回正确的条目大小？
So question: how to create compressed (ZipEntry.DEFLATED or another if exists) zip archive that returns correct size of the entry using only the standard libraries?
我试过此建议但它也不起作用：
I tried this recommendation but it also does not work:
import java.io.*;
import java.util.zip.ZipEntry;
import java.util.zip.ZipInputStream;
import java.util.zip.ZipOutputStream;
public class Main {
public static void main(String[] args) {
File infile = new File("test_file.pdf");
try (
FileInputStream fis = new FileInputStream(infile);
ZipOutputStream zos = new ZipOutputStream(new FileOutputStream("test.zip"));
) {
int bytesRead;
byte[] buffer = new byte[1024];
ZipEntry entry = new ZipEntry("data");
entry.setSize(infile.length());
zos.putNextEntry(entry);
while ((bytesRead = fis.read(buffer)) >= 0)
{
zos.write(buffer, 0, bytesRead);
}
zos.closeEntry();
} catch (IOException e) {
e.printStackTrace();
}
try (
ZipInputStream zis = new ZipInputStream(new BufferedInputStream(
new FileInputStream(new File("test.zip"))));
) {
ZipEntry entry = zis.getNextEntry();
byte[] buffer = new byte[1];
zis.read(buffer);
System.out.println("Entry size: " + entry.getSize());
zis.closeEntry();
} catch (IOException e) {
e.printStackTrace();
}
}
}
输出：
条目大小：-1
推荐答案
你只能这样如果您还设置了CRC和压缩大小，则设置未压缩的大小。由于这些信息之前存储在实际数据之前的标题中，并且 ZipOutputStream 无法回退任意 OutputStream s，在写入和存储它们之后无法计算这些值（但它会计算它们以验证提供的值）。
You can only set the uncompressed size if you also set the CRC and compressed size as well. Since these information are stored before in a header before the actual data and ZipOutputStream can’t rewind arbitrary OutputStreams, it can’t calculate these values while writing and store them afterwards (but it will calculate them for verifying the provided values).
这是一个计算值的解决方案在写作之前通过。它利用了一个事实，如果它由文件支持，你可以回滚一个流。
Here is a solution for calculating the values in one pass before the writing. It utilizes the fact that you can rewind a stream if it is backed by a file.
public static void main(String[] args) throws IOException {
File infile = new File("test_file.pdf");
File outfile = new File("test.zip");
try (FileInputStream fis = new FileInputStream(infile);
FileOutputStream fos = new FileOutputStream(outfile);
ZipOutputStream zos = new ZipOutputStream(fos) ) {
byte[] buffer = new byte[1024];
ZipEntry entry = new ZipEntry("data");
precalc(entry, fis.getChannel());
zos.putNextEntry(entry);
for(int bytesRead; (bytesRead = fis.read(buffer)) >= 0; )
zos.write(buffer, 0, bytesRead);
zos.closeEntry();
}
try(FileInputStream fin = new FileInputStream(outfile);
ZipInputStream zis = new ZipInputStream(fin) ) {
ZipEntry entry = zis.getNextEntry();
System.out.println("Entry size: " + entry.getSize());
System.out.println("Compressed size: " + entry.getCompressedSize());
System.out.println("CRC: " + entry.getCrc());
zis.closeEntry();
}
}
private static void precalc(ZipEntry entry, FileChannel fch) throws IOException {
long uncompressed = fch.size();
int method = entry.getMethod();
CRC32 crc = new CRC32();
Deflater def;
byte[] drain;
if(method != ZipEntry.STORED) {
def = new Deflater(Deflater.DEFAULT_COMPRESSION, true);
drain = new byte[1024];
}
else {
def = null;
drain = null;
}
ByteBuffer buf = ByteBuffer.allocate((int)Math.min(uncompressed, 4096));
for(int bytesRead; (bytesRead = fch.read(buf)) != -1; buf.clear()) {
crc.update(buf.array(), buf.arrayOffset(), bytesRead);
if(def!=null) {
def.setInput(buf.array(), buf.arrayOffset(), bytesRead);
while(!def.needsInput()) def.deflate(drain, 0, drain.length);
}
}
entry.setSize(uncompressed);
if(def!=null) {
def.finish();
while(!def.finished()) def.deflate(drain, 0, drain.length);
entry.setCompressedSize(def.getBytesWritten());
}
entry.setCrc(crc.getValue());
fch.position(0);
}
它处理未压缩和压缩的条目，但不幸的是，只有默认值压缩级别为 ZipOutputStream 没有查询当前级别的方法。因此，如果您更改压缩级别，则必须保持prealc代码同步。或者，您可以将逻辑移动到 ZipOutputStream 的子类中，并使用相同的 Deflater 因此它将自动具有相同的配置。
It handles both, uncompressed and compressed entries, but unfortunately, only with the default compression level as ZipOutputStream has no method for querying the current level. So if you change the compression level you have to keep the precalc code in sync. Alternatively, you could move the logic into a subclass of ZipOutputStream and use the same Deflater so it will automatically have the same configuration.
使用任意源输入流的解决方案需要缓冲整个条目数据。
A solution working with arbitrary source input streams would require buffering of the entire entry data.
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