Caches for internal stores and files

This adds optional caches for configuration stores and
backing data files for data stores.

These stores can be enabled using the system properties
`scm.storeCache.enabled=true` and `scm.cache.dataFileCache.enabled=true`.

In addition, this adds the possibility to overwrite cache configurations
from the guice cache (see file `gcache.xml`) with system properties.
The maximum size of the external group cache for example can be
overwritten with the system property `scm.cache.externalGroups.maximumSize`.

Co-authored-by: René Pfeuffer <rene.pfeuffer@cloudogu.com>

scm-webapp/src/test/java/sonia/scm/cache/GuavaNamedCacheConfigurationTest.java

@@ -0,0 +1,86 @@
+/*
+ * MIT License
+ *
+ * Copyright (c) 2020-present Cloudogu GmbH and Contributors
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+package sonia.scm.cache;
+
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Nested;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.mockito.junit.jupiter.MockitoExtension;
+
+import javax.xml.bind.JAXBContext;
+import javax.xml.bind.JAXBException;
+import java.io.StringReader;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+@ExtendWith(MockitoExtension.class)
+class GuavaNamedCacheConfigurationTest {
+
+  public static final String CACHE_CONFIGURATION =
+    "<caches>" +
+      "  <cache" +
+      "    name=\"sonia.cache.externalGroups\"" +
+      "    maximumSize=\"1000\"" +
+      "  />" +
+      "</caches>";
+
+  @Test
+  void shouldTakeValueFromConfigurationFile() throws JAXBException {
+    GuavaCacheManagerConfiguration configuration = readConfiguration();
+
+    assertThat(configuration.getCaches().get(0).getName()).isEqualTo("sonia.cache.externalGroups");
+    assertThat(configuration.getCaches().get(0).getMaximumSize()).isEqualTo(1000);
+  }
+
+  @Nested
+  class WithProperty {
+
+    @BeforeEach
+    void setProperty() {
+      System.setProperty("scm.cache.externalGroups.maximumSize", "42");
+    }
+
+    @AfterEach
+    void removeProperty() {
+      System.clearProperty("scm.cache.externalGroups.maximumSize");
+    }
+
+    @Test
+    void shouldTakeValueFromPropertyIfPresent() throws JAXBException {
+      GuavaCacheManagerConfiguration configuration = readConfiguration();
+
+      assertThat(configuration.getCaches().get(0).getMaximumSize()).isEqualTo(42);
+    }
+  }
+
+  private static GuavaCacheManagerConfiguration readConfiguration() throws JAXBException {
+    JAXBContext context = JAXBContext.newInstance(GuavaCacheManagerConfiguration.class);
+    return (GuavaCacheManagerConfiguration) context
+      .createUnmarshaller()
+      .unmarshal(new StringReader(CACHE_CONFIGURATION));
+  }
+}