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？
考虑将单个文件test_file.pdf放入zip archive test.zip的代码示例，然后阅读此存档：
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： Entry size: -1
但是如果创建未压缩的zip存档（方法ZipEntry.STORED ），则getSize（）返回正确的大小：
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）： Entry size: 9223192
存在正确entry.getSize()压缩zip存档（例如Ark程序的zip存档）。
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？
我尝试了这个建议，但它也不起作用：
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： Entry size: -1
如果您还设置了CRC和压缩大小，则只能设置未压缩的大小。 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 ，因此在编写和存储它们之后无法计算这些值（但它会计算它们以validation提供的值）。
这是一个在写入之前计算一遍中的值的解决方案。 它利用了一个事实，即如果文件由文件支持，您可以回滚它。
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条目，但不幸的是，只有默认压缩级别，因为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。
使用任意源输入流的解决方案将需要缓冲整个条目数据。
又脏又快
public static void main(String[] args) throws IOException { FileInputStream fis = new FileInputStream( "source.txt" ); FileOutputStream fos = new FileOutputStream( "result.zip" ); ZipOutputStream zos = new ZipOutputStream( fos ); byte[] buf = new byte[fis.available()]; fis.read(buf); ZipEntry e = new ZipEntry( "source.txt" ); updateEntry(e, buf); zos.putNextEntry(e); zos.write(buf); zos.closeEntry(); zos.close(); } private static void updateEntry(ZipEntry entry, byte[] buffer) throws IOException { ByteArrayOutputStream bos = new ByteArrayOutputStream(); ZipOutputStream zos = new ZipOutputStream( bos ); zos.putNextEntry(entry); zos.write(buffer); zos.closeEntry(); zos.close(); bos.close(); }