Added LogEntry and its database adapter

src/main/java/world/bentobox/bentobox/api/logs/LogEntry.java

@@ -0,0 +1,41 @@
+package world.bentobox.bentobox.api.logs;
+
+import java.util.Map;
+
+/**
+ * Represents an event that occurred and that is logged.
+ * <br/>
+ * An {@link world.bentobox.bentobox.database.objects.adapters.AdapterInterface} is provided to be able to save/retrieve
+ * a list of instances of this object to/from the database: {@link world.bentobox.bentobox.database.objects.adapters.LogEntryListAdapter}.
+ *
+ * @author Poslovitch
+ */
+public class LogEntry {
+    private long timestamp;
+    private String type;
+    private Map<String, String> data;
+
+    public LogEntry(String type, Map<String, String> data) {
+        this.timestamp = System.currentTimeMillis();
+        this.type = type;
+        this.data = data;
+    }
+
+    public LogEntry(long timestamp, String type, Map<String, String> data) {
+        this.timestamp = timestamp;
+        this.type = type;
+        this.data = data;
+    }
+
+    public long getTimestamp() {
+        return timestamp;
+    }
+
+    public String getType() {
+        return type;
+    }
+
+    public Map<String, String> getData() {
+        return data;
+    }
+}

src/main/java/world/bentobox/bentobox/database/objects/adapters/LogEntryListAdapter.java

@@ -0,0 +1,73 @@
+package world.bentobox.bentobox.database.objects.adapters;
+
+import world.bentobox.bentobox.api.logs.LogEntry;
+
+import java.util.LinkedHashMap;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.Map;
+
+/**
+ * @author Poslovitch
+ */
+/*  The serialization might look a bit weird here, as I'm using JSON's array of object.
+    This means that, once serialized, the data will look like this (on YAML):
+        history:
+            - timestamp: 0
+              type: "test"
+              data:
+                player: "uuid"
+                action: "ISLAND_LEVEL_UPDATED"
+                value: 45
+            - timestamp: 4181
+              type: "lol"
+              data:
+                help: "yep"
+ */
+public class LogEntryListAdapter implements AdapterInterface<List<LogEntry>, List<Map<String, Object>>> {
+
+    private static final String TIMESTAMP = "timestamp";
+    private static final String TYPE = "type";
+    private static final String DATA = "data";
+
+    @SuppressWarnings("unchecked")
+    @Override
+    public List<LogEntry> deserialize(Object object) {
+        List<LogEntry> result = new LinkedList<>();
+        if (object == null) {
+            return result;
+        }
+
+        List<Map<String, Object>> serialized = (List<Map<String, Object>>) object;
+        for (Map<String, Object> entry : serialized) {
+            long timestamp = (long) entry.get(TIMESTAMP);
+            String type = (String) entry.get(TYPE);
+            Map<String, String> data = (Map<String, String>) entry.get(DATA);
+
+            result.add(new LogEntry(timestamp, type, data));
+        }
+
+        return result;
+    }
+
+    @SuppressWarnings("unchecked")
+    @Override
+    public List<Map<String, Object>> serialize(Object object) {
+        List<Map<String, Object>> result = new LinkedList<>();
+        if (object == null) {
+            return result;
+        }
+
+        List<LogEntry> history = (List<LogEntry>) object;
+        history.forEach(logEntry -> {
+            Map<String, Object> value = new LinkedHashMap<>();
+            value.put(TIMESTAMP, logEntry.getTimestamp());
+            value.put(TYPE, logEntry.getType());
+            value.put(DATA, logEntry.getData());
+
+            result.add(value);
+        });
+
+        return result;
+    }
+}