Package org.eclipse.microprofile.context.spi

Interface ThreadContextProvider

public interface ThreadContextProvider

Third party providers of thread context implement this interface to enable the provided type of context to participate in thread context capture and propagation when the ManagedExecutor and ThreadContext are used to create and contextualize dependent actions and tasks.

Application code must never access the classes within this spi package. Instead, application code uses the ManagedExecutor and ThreadContext interfaces.

The ThreadContextProvider implementation and related classes are packaged within the third party provider's JAR file. The implementation is made discoverable via the standard ServiceLoader mechanism. The JAR file that packages it must include a file of the following name and location,

META-INF/services/org.eclipse.microprofile.context.spi.ThreadContextProvider

The content of the aforementioned file must be one or more lines, each specifying the fully qualified name of a ThreadContextProvider implementation that is provided within the JAR file.

ManagedExecutor and ThreadContext must use the ServiceLoader to identify all available implementations of ThreadContextProvider that can participate in thread context capture and propagation and must invoke them either to capture current thread context or establish default thread context per the configuration of the ManagedExecutor or ThreadContext instance wherever these interfaces are used to create and contextualize dependent actions and tasks.

  • Method Details

    • currentContext

      ThreadContextSnapshot currentContext(Map<String,String> props)
      Captures from the current thread a snapshot of the provided thread context type.
      Parameters:
      props - provided for compatibility with EE Concurrency spec, which allows for specifying a set of 'execution properties' when capturing thread context. Thread context providers that don't supply or use execution properties can ignore this parameter.
      Returns:
      immutable snapshot of the provided type of context, captured from the current thread.
      Throws:
      IllegalStateException - the Transaction context provider may raise this exception if it chooses not to support the optional capability of propagating Transaction context across threads. This exception flows back to the application when the application invokes an operation that captures context, such as runAsync, withContextCapture, and contextualFunction.

    • clearedContext

      ThreadContextSnapshot clearedContext(Map<String,String> props)

      Returns empty/cleared context of the provided type. This context is not captured from the current thread, but instead represents the behavior that you get for this context type when no particular context has been applied to the thread.

      This is used in cases where the provided type of thread context should not be propagated from the requesting thread or inherited from the thread of execution, in which case it is necessary to establish an empty/cleared context in its place, so that an action does not unintentionally inherit context of the thread that happens to run it.

      For example, a security context provider's empty/cleared context ensures there is no authenticated user on the thread. A transaction context provider's empty/cleared context ensures that any active transaction is suspended. And so forth.

      Parameters:
      props - provided for compatibility with EE Concurrency spec, which allows for specifying a set of 'execution properties'. Thread context providers that don't supply or use execution properties can ignore this parameter.
      Returns:
      immutable empty/default context of the provided type.

    • getThreadContextType

      String getThreadContextType()

      Returns a human readable identifier for the type of thread context that is captured by this ThreadContextProvider implementation.

      To ensure portability of applications, this will typically be a keyword that is defined by the same specification that defines the thread context type, or by a related MicroProfile specification.

      The ThreadContext interface defines constants for some commonly used thread context types, including Application, Security, Transaction, and CDI.

      The application can use the values documented for the various thread context types when configuring a ManagedExecutor or ThreadContext to capture and propagate only specific types of thread context.

      For example:

      
 ManagedExecutor executor = ManagedExecutor.builder()
                                           .propagated(ThreadContext.CDI)
                                           .cleared(ThreadContext.ALL_REMAINING)
                                           .build();

      It is an error for multiple thread context providers of identical type to be simultaneously available (for example, two providers of CDI context found on the ServiceLoader). If this is found to be the case, ManagedExecutor and ThreadContext must fail to inject.

      The identifiers None and Remaining have special meaning, as defined by ThreadContext, and must not be returned from this method by any ThreadContextProvider.

      Returns:
      identifier for the provided type of thread context.