Closes gh-7174
See gh-7213

Closes gh-7202

* pr/6954:
  Improve systemd service documentation

Closes gh-6954

Closes gh-7016

* pr/7043:
  Speed up Travis build

Modify to use standard mode and directory cache for Travis CI build.

Closes gh-7043

* pr/7193:
  Polish contribution
  Add a missing return

Add missing test

Closes gh-7193

This commit adds a missing`return` in `getDataSourceBeanDefinition()`.

See gh-7193

Closes gh-7208

* pr/6966:
  Remove unused

Closes gh-6966

* pr/7203:
  Correct typo in docs

Closes gh-7203

See gh-7197

ErrorPageFilter contained an optimisation for looking up the path
of an error page by exception type. For cases where there was no
mapping for the type of the exception that was thrown but there
was a mapping for one of its super classes, it was intended to
speed up the lookup. Unfortunately, there was a bug in the
implementation which meant that the optimisation had no effect.

Analysis with JMH reveals that for an Exception with a deep type
hierarchy, such as Spring Framework's UnsatisfiedDependencyException,
and an error page mapping for Exception, searching up the hierarchy
until a mapping is found takes 0.0000001s. With the same mapping,
a lookup for Exception takes 0.00000001s, i.e. it's 10x faster.
The optimisation, when correctly implemented, brings the time for
UnsatisfiedDependencyException down to 0.00000001s and into line
with a lookup for Exception. However, the amount of time involved is
so small compared to the overall time spent processing a request that
the added complexity of the optimisation is not justified.

Closes gh-7010

See gh-7101

Every classes that's compiled by Kotlin is annotated with
kotlin.Metadata. The attributes of this annotation always differ so
if they are used in the cache key, context caching will effectively
be disabled.

This commit updates the key used by ImportsContextCustomizer to
ignore the kotlin.Metadata annotation. Additionally, to align with
with Java where annotations in java.lang.annotation are ignored,
annotations in kotlin.annotation are also ignored.

Closes gh-7101

Closes gh-7112

See gh-6991
Closes gh-7183

* gh-7183:
  Update docs on using Thmyeleaf 3 to reference latest version

Closes gh-7183

URL.getContent() is shorthand for URL.openConnection().getContent().
It creates an InputStream that isn't explicitly closed. This means
that a file handle remains open until the URLConnection is garbage
collected. This can lead to the process exceeding the limit for open
files.

Previously, LaunchedURLClassLoader was using getConent() when
proactively defining a package for a class that is about to be loaded.
getContent() was used to access nested jar files to check if they
contained the package and, if so, to retrieve the jar's manifest.

In place of using getContent(), this commit uses JarURLConnection's
getJarFile() method which provides access to the JarFile without the
unwanted side-effect of opening an input stream.

Closes gh-7180

Closes gh-7092
Closes gh-7093

Previously, a relative PID folder was not handled correctly when
running stop, status, or force_reload. This meant that a service
could be started when configured to use a relative pid file, but
then could not be stopped.

The PID folder should be treated as relative to the service's jar
file. This commit updates stop, status, and force_reload to push the
jar file's directory so that this is now the case for those three
commands.

Closes gh-7092

Closes gh-7144

Closes gh-7145

Rather than disabling checkstyle altogether, this commit enables it
again, relaxing the javadoc requirement only.

See gh-7142

Closes gh-7142

Closes gh-7147

Closes gh-7138

* pr/7137:
  Add missing parentheses

Closes gh-7137

Closes gh-2642

Note: the fully-qualified references to @Configuration in some of the
test configuration classes are required to work around a bug in javac.
1.8.0_102 (and earlier). Without them, compilation fails as it cannot
resolve the symbol despite the import statement and the unqualified
references working elsewhere in the same source file.

Closes gh-7056

See gh-7080