What is the lib\modules file in JRE 9 installation directory?

If you have JRE 9 installed, you will see the lib\modules file in the JDK 9 installation directory. It is the runtime JImage file of all Java language modules and some JDK tool modules.

You can list all modules and classes in lib\modules using the "jimage list" command:

C:>\fyicenter\jdk-9.0.4\bin\jimage list \fyicenter\jre-9.0.4\lib\modules

jimage: \fyicenter\jre-9.0.4\lib\modules

Module: java.activation
    META-INF/mailcap.default
    META-INF/mimetypes.default
    com/sun/activation/registries/LineTokenizer.class
    com/sun/activation/registries/LogSupport.class
    com/sun/activation/registries/MailcapFile.class
    com/sun/activation/registries/MailcapParseException.class
    com/sun/activation/registries/MailcapTokenizer.class
    com/sun/activation/registries/MimeTypeEntry.class
    com/sun/activation/registries/MimeTypeFile.class
    javax/activation/ActivationDataFlavor.class
    javax/activation/CommandInfo$Beans$1.class
    javax/activation/CommandInfo$Beans.class
    javax/activation/CommandInfo.class
    javax/activation/CommandMap.class
    javax/activation/CommandObject.class
    javax/activation/DataContentHandler.class
    javax/activation/DataContentHandlerFactory.class
    javax/activation/DataHandler$1.class
    javax/activation/DataHandler.class
    javax/activation/DataHandlerDataSource.class
    javax/activation/DataSource.class
    javax/activation/DataSourceDataContentHandler.class
    javax/activation/FileDataSource.class
    javax/activation/FileTypeMap.class
    javax/activation/MailcapCommandMap$1.class
    javax/activation/MailcapCommandMap.class
    javax/activation/MimeType.class
    javax/activation/MimeTypeParameterList.class
    javax/activation/MimeTypeParseException.class
    javax/activation/MimetypesFileTypeMap$1.class
    javax/activation/MimetypesFileTypeMap.class
    javax/activation/ObjectDataContentHandler.class
    javax/activation/SecuritySupport$1.class
    javax/activation/SecuritySupport$2.class
    javax/activation/SecuritySupport$3.class
    javax/activation/SecuritySupport$4.class
    javax/activation/SecuritySupport$5.class
    javax/activation/SecuritySupport.class
    javax/activation/URLDataSource.class
    javax/activation/UnsupportedDataTypeException.class
    module-info.class

Module: java.base
    META-INF/services/java.nio.file.spi.FileSystemProvider
    com/sun/crypto/provider/AESCipher$AES128_CBC_NoPadding.class
    com/sun/crypto/provider/AESCipher$AES128_CFB_NoPadding.class
    ...

⇒ JDK 9 Modules List

⇐ JDK 9 lib/src.zip - Source Code

⇑ Download and Use JDK 9

⇑⇑ FAQ for JDK (Java Development Kit)