Resolve "ElementCollection aus AuditLogEvent entfernen"

Related to #542 (closed)

src/main/java/at/ac/uibk/gitsearch/domain/util/MapToJsonConverter.java

+package at.ac.uibk.gitsearch.domain.util;
+
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+import javax.persistence.AttributeConverter;
+import javax.persistence.Converter;
+import org.apache.tika.utils.StringUtils;
+
+@Converter
+@SuppressWarnings({ "PMD.AvoidThrowingRawExceptionTypes", "PMD.AvoidCatchingGenericException" })
+public class MapToJsonConverter implements AttributeConverter<Map<String, String>, String> {
+
+  private final ObjectMapper objectMapper = new ObjectMapper();
+
+  @Override
+  public String convertToDatabaseColumn(Map<String, String> attribute) {
+    if (attribute == null) {
+      return null;
+    }
+
+    try {
+      return objectMapper.writeValueAsString(attribute);
+    } catch (JsonProcessingException e) {
+      throw new RuntimeException("Error saving map to Json", e);
+    }
+  }
+
+  @Override
+  public Map<String, String> convertToEntityAttribute(String dbData) {
+    if (StringUtils.isEmpty(dbData)) {
+      return new ConcurrentHashMap<>();
+    }
+    try {
+      return objectMapper.readValue(dbData, Map.class);
+    } catch (Exception e) {
+      throw new RuntimeException("Error converting JSON to map", e);
+    }
+  }
+}