prepare 5.0.0 release

[LaunchDarklyCI]

[5.0.0] - 2020-06-02

This is a major rewrite that introduces a cleaner API design, adds new features, and makes the SDK code easier to maintain and extend. See the Java 4.x to 5.0 migration guide for an in-depth look at the changes in this version; the following is a summary.

(For early adopters who have used the the 5.0.0-rc2 beta release: some things have changed between 5.0.0-rc2 and this full release. The 5.0.0-rc2 release notes have been updated with a section describing these changes.)

Added:

• You can tell the SDK to notify you whenever a feature flag's configuration has changed (either in general, or in terms of its result for a specific user), using LDClient.getFlagTracker(). (#83)
• You can monitor the status of the SDK's data source (which normally means the streaming connection to the LaunchDarkly service) with LDClient.getDataSourceStatusProvider(). This allows you to check the current connection status, and to be notified if this status changes. (#184)
• You can monitor the status of a persistent data store with LDClient.getDataStoreStatusProvider(). This allows you to check whether database updates are succeeding, to be notified if this status changes, and to get caching statistics.
• The FileData tool now supports reading flag data from a classpath resource as if it were a data file. See FileDataSourceBuilder.classpathResources(). (#193)
• LDConfig.Builder.logging() is a new configuration category for options related to logging. Currently the only such option is escalateDataSourceOutageLoggingAfter, which controls the new connection failure logging behavior described below.
• LDConfig.Builder.threadPriority() allows you to set the priority for worker threads created by the SDK.
• The UserAttribute class provides a less error-prone way to refer to user attribute names in configuration, and can also be used to get an arbitrary attribute from a user.
• The LDGson and LDJackson classes allow SDK classes like LDUser to be easily converted to or from JSON using the popular Gson and Jackson frameworks.

Changed (requirements/dependencies/build):

• The minimum supported Java version is now 8.
• The SDK no longer exposes a Gson dependency or any Gson types.
• Third-party libraries like Gson, Guava, and OkHttp that are used internally by the SDK have been updated to newer versions since Java 7 compatibility is no longer required. (#158)
• Code coverage reports and JMH benchmarks are now generated in every build. Unit test coverage of the entire SDK codebase has been greatly improved.

Changed (API changes):

• Package names have changed: the main SDK classes are now in com.launchdarkly.sdk and com.launchdarkly.sdk.server.
• Many rarely-used classes and interfaces have been moved out of the main SDK package into com.launchdarkly.sdk.server.integrations and com.launchdarkly.sdk.server.interfaces.
• The type java.time.Duration is now used for configuration properties that represent an amount of time, instead of using a number of milliseconds or seconds.
• LDClient.initialized() has been renamed to isInitialized().
• LDClient.intVariation() and doubleVariation() now return int and double, not the nullable Integer and Double.
• EvaluationDetail.getVariationIndex() now returns int instead of Integer.
• EvaluationReason is now a single concrete class rather than an abstract base class.
• The component interfaces FeatureStore and UpdateProcessor have been renamed to DataStore and DataSource. The factory interfaces for these components now receive SDK configuration options in a different way that does not expose other components' configurations to each other.
• The PersistentDataStore interface for creating your own database integrations has been simplified by moving all of the serialization and caching logic into the main SDK code.

Changed (behavioral changes):

• SLF4J logging now uses a simpler, more stable set of logger names instead of using the names of specific implementation classes that are subject to change. General messages are logged under com.launchdarkly.sdk.server.LDClient, while messages about specific areas of functionality are logged under that name plus .DataSource (streaming, polling, file data, etc.), .DataStore (database integrations), .Evaluation (unexpected errors during flag evaluations), or .Events (analytics event processing).
• If analytics events are disabled with Components.noEvents(), the SDK now avoids generating any analytics event objects internally. Previously they were created and then discarded, causing unnecessary heap churn.
• Network failures and server errors for streaming or polling requests were previously logged at ERROR level in most cases but sometimes at WARN level. They are now all at WARN level, but with a new behavior: if connection failures continue without a successful retry for a certain amount of time, the SDK will log a special ERROR-level message to warn you that this is not just a brief outage. The amount of time is one minute by default, but can be changed with the new logDataSourceOutageAsErrorAfter option in LoggingConfigurationBuilder. (#190)
• Many internal methods have been rewritten to reduce the number of heap allocations in general.
• Evaluation of rules involving regex matches, date/time values, and semantic versions, has been speeded up by pre-parsing the values in the rules.
• Evaluation of rules involving an equality match to multiple values (such as "name is one of X, Y, Z") has been speeded up by converting the list of values to a Set.
• The number of worker threads maintained by the SDK has been reduced so that most intermittent background tasks, such as listener notifications, event flush timers, and polling requests, are now dispatched on a single thread. The delivery of analytics events to LaunchDarkly still has its own thread pool because it is a heavier-weight task with greater need for concurrency.
• In polling mode, the poll requests previously ran on a dedicated worker thread that inherited its priority from the application thread that created the SDK. They are now on the SDK's main worker thread, which has Thread.MIN_PRIORITY by default (as all the other SDK threads already did) but the priority can be changed as described above.
• When using a persistent data store such as Redis, if there is a database outage, the SDK will wait until the end of the outage and then restart the stream connection to ensure that it has the latest data. Previously, it would try to restart the connection immediately and continue restarting if the database was still not available, causing unnecessary overhead.

Fixed:

• LDClient.version() previously could not be used if the SDK classes were not packaged in their original jar. It now works correctly regardless of deployment details.

Removed:

• All types and methods that were deprecated as of Java SDK 4.13.0 have been removed. This includes many LDConfig.Builder() methods, which have been replaced by the modular configuration syntax that was already added in the 4.12.0 and 4.13.0 releases. See the migration guide for details on how to update your configuration code if you were using the older syntax.
• The Redis integration is no longer built into the main SDK library. See: https://github.com/launchdarkly/java-server-sdk-redis
• The deprecated New Relic integration has been removed.