If you are using libraries that are already compiled and packaged into JARs, and signed by the author, you do not have to worry about signing them. But say, you've used someone else's source code (open source hopefully) and have compiled it on your own machine, you must remove the existing signature and re-sign that package. If you are using Java applets, they must be signed now, unless you enjoy a mountain of pain.
Now, this also applies to the packaged libraries within your packaged jar. If they have already been signed, leave them alone. But if you must sign them, make sure you remove any existing certificates from the JAR file before you do so, the same way as your main applet.
Additional information that may help:
Your MANIFEST.mf file in all JARs must contain entries for the the properties, as shown in the example below:
Application-Library-Allowable-Codebase: *
Permissions: all-permissions
Caller-Allowable-Codebase: *
Codebase: *
Application-Name: POSInterface
TIP
If you're deploying a bunch of applets to a web application, I like to automate this whole process of modifying the manifest and code-signing with a batch file and text file containing the above properties that need to be in the manifest.mf file, named addToManifest.txt. Here is an example of how it's done:
@ECHO off
ECHO Changing manifest files for all...
jar ufm Applet_RFID.jar addToManifest.txt
jar ufm FingerPrintReader.jar addToManifest.txt
jar ufm jzebra.jar addToManifest.txt
jar ufm POSInterface.jar addToManifest.txt
jar ufm lib\access-bridge-32.jar addToManifest.txt
jar ufm lib\addToManifest.txt addToManifest.txt
jar ufm lib\dnsns.jar addToManifest.txt
jar ufm lib\dpuareu.jar addToManifest.txt
jar ufm lib\epsonupos.admin.jar addToManifest.txt
jar ufm lib\epsonupos.core.v1.13.0001.jar addToManifest.txt
jar ufm lib\epsonupos.H2000.jar addToManifest.txt
jar ufm lib\epsonupos.H6000IV.jar addToManifest.txt
jar ufm lib\epsonupos.jar addToManifest.txt
jar ufm lib\epsonupos.T20.jar addToManifest.txt
jar ufm lib\epsonupos.T81.jar addToManifest.txt
jar ufm lib\epsonupos.T81II.jar addToManifest.txt
jar ufm lib\epsonupos.T82.jar addToManifest.txt
jar ufm lib\epsonupos.T88V.jar addToManifest.txt
jar ufm lib\epsonupos.trace.jar addToManifest.txt
jar ufm lib\HWHydraSO.jar addToManifest.txt
jar ufm lib\jaccess.jar addToManifest.txt
jar ufm lib\jcl_editor.jar addToManifest.txt
jar ufm lib\jpos113-controls.jar addToManifest.txt
jar ufm lib\jpos113.jar addToManifest.txt
jar ufm lib\jssc_qz.jar addToManifest.txt
jar ufm lib\localedata.jar addToManifest.txt
jar ufm lib\plugin.jar addToManifest.txt
jar ufm lib\pos.jar addToManifest.txt
jar ufm lib\pos.v3.0001.jar addToManifest.txt
jar ufm lib\stario.jar addToManifest.txt
jar ufm lib\starjavapos.jar addToManifest.txt
jar ufm lib\sunec.jar addToManifest.txt
jar ufm lib\sunjce_provider.jar addToManifest.txt
jar ufm lib\sunmscapi.jar addToManifest.txt
jar ufm lib\sunpkcs11.jar addToManifest.txt
jar ufm lib\Symbol.RFID.API3.jar addToManifest.txt
jar ufm lib\uposcommon.core.v1.13.0001.jar addToManifest.txt
jar ufm lib\uposcommon.jar addToManifest.txt
jar ufm lib\xercesImpl.jar addToManifest.txt
jar ufm lib\xml-apis.jar addToManifest.txt
jar ufm lib\zipfs.jar addToManifest.txt
ECHO All JAR manifest have been altered.
PAUSE
ECHO Signing all Applets...
jarsigner Applet_RFID.jar -keystore "C:\Certificate\YourCertificate.key" <keystoreName> -storepass <SecretKey>
jarsigner FingerPrintReader.jar -keystore "C:\Certificate\YourCertificate.key" <keystoreName> -storepass <SecretKey>
jarsigner jzebra.jar -keystore "C:\Certificate\YourCertificate.key" <keystoreName> -storepass <SecretKey>
jarsigner POSInterface.jar -keystore "C:\Certificate\YourCertificate.key" <keystoreName> -storepass <SecretKey>
jarsigner lib\access-bridge-32.jar -keystore "C:\Certificate\YourCertificate.key" <keystoreName> -storepass <SecretKey>
jarsigner lib\-keystore "C:\Certificate\YourCertificate.key" <keystoreName> -storepass <SecretKey>
jarsigner lib\dnsns.jar -keystore "C:\Certificate\YourCertificate.key" <keystoreName> -storepass <SecretKey>
jarsigner lib\dpuareu.jar -keystore "C:\Certificate\YourCertificate.key" <keystoreName> -storepass <SecretKey>
jarsigner lib\epsonupos.admin.jar -keystore "C:\Certificate\YourCertificate.key" <keystoreName> -storepass <SecretKey>
jarsigner lib\epsonupos.core.v1.13.0001.jar -keystore "C:\Certificate\YourCertificate.key" <keystoreName> -storepass <SecretKey>
jarsigner lib\epsonupos.H2000.jar -keystore "C:\Certificate\YourCertificate.key" <keystoreName> -storepass <SecretKey>
jarsigner lib\epsonupos.H6000IV.jar -keystore "C:\Certificate\YourCertificate.key" <keystoreName> -storepass <SecretKey>
jarsigner lib\epsonupos.jar -keystore "C:\Certificate\YourCertificate.key" <keystoreName> -storepass <SecretKey>
jarsigner lib\epsonupos.T20.jar -keystore "C:\Certificate\YourCertificate.key" <keystoreName> -storepass <SecretKey>
jarsigner lib\epsonupos.T81.jar -keystore "C:\Certificate\YourCertificate.key" <keystoreName> -storepass <SecretKey>
jarsigner lib\epsonupos.T81II.jar -keystore "C:\Certificate\YourCertificate.key" <keystoreName> -storepass <SecretKey>
jarsigner lib\epsonupos.T82.jar -keystore "C:\Certificate\YourCertificate.key" <keystoreName> -storepass <SecretKey>
jarsigner lib\epsonupos.T88V.jar -keystore "C:\Certificate\YourCertificate.key" <keystoreName> -storepass <SecretKey>
jarsigner lib\epsonupos.trace.jar -keystore "C:\Certificate\YourCertificate.key" <keystoreName> -storepass <SecretKey>
jarsigner lib\HWHydraSO.jar -keystore "C:\Certificate\YourCertificate.key" <keystoreName> -storepass <SecretKey>
jarsigner lib\jaccess.jar -keystore "C:\Certificate\YourCertificate.key" <keystoreName> -storepass <SecretKey>
jarsigner lib\jcl_editor.jar -keystore "C:\Certificate\YourCertificate.key" <keystoreName> -storepass <SecretKey>
jarsigner lib\jpos113-controls.jar -keystore "C:\Certificate\YourCertificate.key" <keystoreName> -storepass <SecretKey>
jarsigner lib\jpos113.jar -keystore "C:\Certificate\YourCertificate.key" <keystoreName> -storepass <SecretKey>
jarsigner lib\jssc_qz.jar -keystore "C:\Certificate\YourCertificate.key" <keystoreName> -storepass <SecretKey>
jarsigner lib\localedata.jar -keystore "C:\Certificate\YourCertificate.key" <keystoreName> -storepass <SecretKey>
jarsigner lib\plugin.jar -keystore "C:\Certificate\YourCertificate.key" <keystoreName> -storepass <SecretKey>
jarsigner lib\pos.jar -keystore "C:\Certificate\YourCertificate.key" <keystoreName> -storepass <SecretKey>
jarsigner lib\pos.v3.0001.jar -keystore "C:\Certificate\YourCertificate.key" <keystoreName> -storepass <SecretKey>
jarsigner lib\stario.jar -keystore "C:\Certificate\YourCertificate.key" <keystoreName> -storepass <SecretKey>
jarsigner lib\starjavapos.jar -keystore "C:\Certificate\YourCertificate.key" <keystoreName> -storepass <SecretKey>
jarsigner lib\sunec.jar -keystore "C:\Certificate\YourCertificate.key" <keystoreName> -storepass <SecretKey>
jarsigner lib\sunjce_provider.jar -keystore "C:\Certificate\YourCertificate.key" <keystoreName> -storepass <SecretKey>
jarsigner lib\sunmscapi.jar -keystore "C:\Certificate\YourCertificate.key" <keystoreName> -storepass <SecretKey>
jarsigner lib\sunpkcs11.jar -keystore "C:\Certificate\YourCertificate.key" <keystoreName> -storepass <SecretKey>
jarsigner lib\Symbol.RFID.API3.jar -keystore "C:\Certificate\YourCertificate.key" <keystoreName> -storepass <SecretKey>
jarsigner lib\uposcommon.core.v1.13.0001.jar -keystore "C:\Certificate\YourCertificate.key" <keystoreName> -storepass <SecretKey>
jarsigner lib\uposcommon.jar -keystore "C:\Certificate\YourCertificate.key" <keystoreName> -storepass <SecretKey>
jarsigner lib\xercesImpl.jar -keystore "C:\Certificate\YourCertificate.key" <keystoreName> -storepass <SecretKey>
jarsigner lib\xml-apis.jar -keystore "C:\Certificate\YourCertificate.key" <keystoreName> -storepass <SecretKey>
jarsigner lib\zipfs.jar -keystore "C:\Certificate\YourCertificate.key" <keystoreName> -storepass <SecretKey>
ECHO All JAR files have been signed.
PAUSE