How to verify jar entity certificate?

Question

If I ask for Certificates[] method JarEntity.getCertificates() returns null.
How to get JarEntity certificates?
JarInputStream jar = null;
try {
     jar = new JarInputStream(new FileInputStream("e:/out/p1.jar"));
     JarEntry je = null;
     while ((je = jar.getNextJarEntry()) != null) {
          System.out.println("--------------------");
          System.out.println(je);
          byte[] b = new byte[3000];
          int l = jar.read(b);
          System.out.println("len: " + l);
          Certificate[] certs = je.getCertificates();
          System.out.println("certs: " + certs);
} catch (Exception e) {
     e.printStackTrace();
} finally {
     if (jar != null) {
          try {
               jar.close();
          } catch (Exception e) {
               // ignore
}result
META-INF/GMNA.SF
len: 203
certs: null
META-INF/GMNA.DSA
len: 664
certs: null
org/x4444/p1/Superp1.class
len: 471
certs: null
Why certs for org/x4444/p1/Superp1.class == null?
the jar was signed :
E:\out>c:\j2sdk1.4.2_13\bin\jarsigner.exe p1.jar gmna
and verified
E:\out>c:\j2sdk1.4.2_13\bin\jarsigner.exe -verify -verbose p1.jar
104 Tue Jul 17 15:41:32 MSD 2007 META-INF/MANIFEST.MF
203 Tue Jul 17 15:41:32 MSD 2007 META-INF/GMNA.SF
1033 Tue Jul 17 15:41:32 MSD 2007 META-INF/GMNA.DSA
smk 471 Tue Jul 17 15:14:56 MSD 2007 org/x4444/p1/Superp1.class
s = signature was verified
m = entry is listed in manifest
k = at least one certificate was found in keystore
i = at least one certificate was found in identity scope
jar verified.

Answer 1

Here is my piece of code to make it
          JarFile jarFile = new JarFile(jarAdress);               
          JarEntry userEntry=jarFile.getJarEntry("userData.xml");
//          *************************** reading from the entry input stream until the end of the stream has been reached. :)***************
          InputStream jarEntryInputStream = jarFile.getInputStream(userEntry);
          int i=0;
          while (jarEntryInputStream.read()!=-1){   
               i=i+1; //System.out.println("lecture du byte "+i);
          jarEntryInputStream.close();
          //Read jar certificat
          Certificate[] certificates = userEntry.getCertificates();
          Certificate jarCertificate = certificates[0]; //read first certificate of array if only one     
          InputStream jarEntryInputStream = jarFile.getInputStream(userEntry);
          int i=0;
          while (jarEntryInputStream.read()!=-1){   
               i=i+1; //System.out.println("lecture du byte "+i);
          jarEntryInputStream.close();
          //Read jar certificat
          Certificate[] certificates = userEntry.getCertificates();
          Certificate jarCertificate = certificates[0];