ppkarwasz commented on code in PR #2374:
URL: https://github.com/apache/logging-log4j2/pull/2374#discussion_r1527192000
##########
log4j-api/src/main/java/org/apache/logging/log4j/spi/Provider.java:
##########
@@ -20,39 +20,135 @@
import java.net.URL;
import java.util.Properties;
import org.apache.logging.log4j.Logger;
+import org.apache.logging.log4j.simple.SimpleLoggerContextFactory;
import org.apache.logging.log4j.status.StatusLogger;
+import org.apache.logging.log4j.util.Constants;
+import org.apache.logging.log4j.util.Lazy;
+import org.apache.logging.log4j.util.LoaderUtil;
+import org.apache.logging.log4j.util.PropertiesUtil;
/**
- * Model class for a Log4j 2 provider. The properties in this class correspond
to the properties used in a
- * {@code META-INF/log4j-provider.properties} file. Note that this class is
automatically created by Log4j and should
- * not be used by providers.
+ * Service class used to bind the Log4j API with an implementation.
+ * <p>
+ * Implementors should register an implementation of this class with
{@link java.util.ServiceLoader}.
+ * </p>
+ * <p>
+ * <strong>Deprecated:</strong> the automatic registration of providers
from
+ * {@code META-INF/log4j-provider.properties} is supported for
compatibility reasons. Support for this file will
+ * be dropped in a future version.
+ * </p>
*/
public class Provider {
+ protected static final String CURRENT_VERSION = "2.6.0";
+
/**
* Property name to set for a Log4j 2 provider to specify the priority of
this implementation.
+ * @deprecated since 2.24.0
*/
+ @Deprecated
public static final String FACTORY_PRIORITY = "FactoryPriority";
+
/**
- * Property name to set to the implementation of {@link
org.apache.logging.log4j.spi.ThreadContextMap}.
+ * Property name to set to the implementation of {@link ThreadContextMap}.
+ * @deprecated since 2.24.0
*/
+ @Deprecated
public static final String THREAD_CONTEXT_MAP = "ThreadContextMap";
+
/**
- * Property name to set to the implementation of {@link
org.apache.logging.log4j.spi.LoggerContextFactory}.
+ * Property name to set to the implementation of {@link
LoggerContextFactory}.
+ * @deprecated since 2.24.0
*/
+ @Deprecated
public static final String LOGGER_CONTEXT_FACTORY = "LoggerContextFactory";
- private static final Integer DEFAULT_PRIORITY = Integer.valueOf(-1);
+ /**
+ * System property used to specify the class name of the provider to use.
+ * @since 2.24.0
+ */
+ public static final String PROVIDER_PROPERTY_NAME = "log4j.provider";
+
+ // Bundled context map implementations
+ private static final String BASE =
"org.apache.logging.log4j.internal.map.";
+
+ /**
+ * Constant used to disable the {@link ThreadContextMap}.
+ * <p>
+ * <strong>Warning:</strong> the value of this constant does not point
to a concrete class name.
+ * </p>
+ * @see #getThreadContextMap
+ */
+ public static final String NO_OP_CONTEXT_MAP = BASE + "NoOp";
+
+ /**
+ * Constant used to select a web application-safe implementation of {@link
ThreadContextMap}.
+ * <p>
+ * This implementation only binds JRE classes to {@link ThreadLocal}
variables.
+ * </p>
+ * <p>
+ * <strong>Warning:</strong> the value of this constant does not point
to a concrete class name.
+ * </p>
+ * @see #getThreadContextMap
+ */
+ public static final String WEB_APP_CONTEXT_MAP = BASE + "WebApp";
+
+ /**
+ * Constant used to select a copy-on-write implementation of {@link
ThreadContextMap}.
+ * <p>
+ * <strong>Warning:</strong> the value of this constant does not point
to a concrete class name.
+ * </p>
+ * @see #getThreadContextMap
+ */
+ public static final String COPY_ON_WRITE_CONTEXT_MAP = BASE +
"CopyOnWrite";
+
+ /**
+ * Constant used to select a garbage-free implementation of {@link
ThreadContextMap}.
+ * <p>
+ * This implementation must ensure that common operations don't create
new object instances. The drawback is
+ * the necessity to bind custom classes to {@link ThreadLocal}
variables.
+ * </p>
+ * <p>
+ * <strong>Warning:</strong> the value of this constant does not point
to a concrete class name.
+ * </p>
+ * @see #getThreadContextMap
+ */
+ public static final String GARBAGE_FREE_CONTEXT_MAP = BASE + "GarbageFree";
Review Comment:
You are right, they could be `protected`.
The reason I introduced these constants is:
- half of these implementations are package-private. An implementation of
`Provider` can not instantiate them, but `Provider` itself can. To use these
context maps an implementation should:
1. implement `#getThreadContextMap` and return one of these special
constants,
2. make a call to `super.createThreadContextMap()` in its
`#createThreadContextMap` implementation.
- I wanted to separate the characteristics of the context map, from the
implementation. So the constant `WebApp` can switch to @jengebr's
implementation under the hood. Probably I should make these constants shorter.
BTW: IMHO the inclusion of `ThreadContextMap` implementations in the
`log4j-api` unnecessarily bloats the artifact. `ThreadContext` is not a
standalone service for users to store thread-dependent data (although I saw
some users use it for this purpose). It must be tightly linked to the `Logger`
implementation. As such, except Log4j Core, no other Log4j API implementation
requires these 3 implementations.
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