Entry point

The entry point for accessing the Windows registry is method Registry.local(). It returns a reference to the local Windows registry. This reference contains public fields for each of the available root registry keys. From these, use the resolve method to get the registry key you need. Note that registry key names can contain forward slashes, so you need to use backslashes to separate keys. From there you can access the registry key's sub keys and values.

Registry values

Unlike several other libraries for working with the Windows registry, registry values are not returned as strings. Instead, class RegistryValue defines several sub classes, one for each of the known registry value types. For instance, StringValue is used for string values, DWordValue for DWORD (int) values, etc. This allows you to retrieve and set values using proper types, instead of having to convert everything to and from strings.

In addition to retrieving registry values as instances of RegistryValue or a sub class of RegistryValue, class RegistryKey provides some utility methods to retrieve registry values as string, DWORD (int) or QWORD (long), as these are considered the most used types.

Handles

Operations can be directly called on registry keys. However, for non-root keys this opens a connection to the Windows registry for every operation. If you need to perform several operations on a single registry key, you should consider calling one of its handle methods. The returned handle allows you to perform the same operations with the same method signatures using a single connection to the Windows registry.

Transactions

By default, any interaction with the Windows registry does not use transactions. Using class TransactionalState it's possible to run code within one of the following transactional states, based on Jakarta EE and Spring transactional states:

• TransactionalState mandatory will reuse an existing transaction if present, or throw an exception otherwise.
• TransactionalState.required will reuse an existing transaction if present, otherwise create a new one.
• TransactionalState.requiresNew will create a new transaction.
• TransactionalState.supports will use an existing transaction if present, otherwise work without a transaction.
• TransactionalState.notSupported will ignore any existing transaction.
• TransactionalState.never will throw an exception if an existing transaction is present.

While nested transactions are not supported by Windows, nesting TransactionalState calls is supported. The innermost call will be leading for any interaction with the Windows registry. However, mixing different transactional states for the same registry keys may cause Windows to automatically rollback one or more transactions.

Remote registries

Using method Registry.at you can connect to the Windows registry on a remote machine, provided the user the JVM is running as has the rights to do so. Apart from the entry point, remote registry keys work exactly like regular registry keys. This includes using the resolve method.

Implementation details

Interaction with the Windows registry is done through the Foreign Function and Memory (FFM) API. This has some benefits:

• Native interaction with the Windows registry instead of using commands like REG QUERY provides better performance.
• Native interaction with the Windows registry instead of piggybacking on Java internal classes like java.util.Preferences provides greater compatibility between Java versions.
• FFM is part of the Java core libraries. There is no need to install any libraries manually. There is not even need to install any runtime dependencies.