Optionally specify limit for number of entities in a record.

This is a brute-force approach to dealing with OOM situations when Alma records have an excessive number of items (e.g. 99374518570506441: >12000 entities = ~10 GB heap for the Record instance).

Use Metafix instance setter `setMaxEntityCount(int)` or set system property `org.metafacture.metafix.maxEntityCount=<int>`.

Alternative options:

- Increase maximum heap size for JVM.
- Significantly reduce memory requirement for Record instances.

metafix-runner/build.gradle

@@ -47,3 +47,13 @@ application {
     applicationDefaultJvmArgs = ["-agentlib:hprof=heap=sites,cpu=samples,depth=${depth},cutoff=${cutoff},file=${file}.hprof.txt"]
   }
 }
+
+tasks.withType(JavaExec) {
+  doFirst {
+    def prefix = project.group + '.'
+
+    System.properties.each { k, v ->
+      if (k.startsWith(prefix)) systemProperties[k] = v
+    }
+  }
+}

metafix/src/main/java/org/metafacture/metafix/Metafix.java

@@ -93,6 +93,7 @@ public class Metafix implements StreamPipe<StreamReceiver>, Maps { // checkstyle
     private boolean repeatedFieldsToEntities;
     private boolean strictnessHandlesProcessExceptions;
     private int entityCount;
+    private int maxEntityCount = Integer.getInteger("org.metafacture.metafix.maxEntityCount", -1);
 
     public Metafix() {
         this(NO_VARS);
@@ -305,22 +306,36 @@ public void startEntity(final String name) {
             throw new IllegalArgumentException("Entity name must not be null.");
         }
 
+        ++entityCount;
+        if (maxEntityCountExceeded()) {
+            LOG.debug("Maximum number of entities exceeded: {}/{}", entityCount, maxEntityCount);
+            return;
+        }
+
         final Value value = isArrayName(name) ? Value.newArray() : Value.newHash();
         addValue(name, value);
         entities.add(value);
 
-        entityCountStack.push(++entityCount);
+        entityCountStack.push(entityCount);
         flattener.startEntity(name);
     }
 
     @Override
     public void endEntity() {
+        if (maxEntityCountExceeded()) {
+            return;
+        }
+
         entityCountStack.pop();
         flattener.endEntity();
     }
 
     @Override
     public void literal(final String name, final String value) {
+        if (entityCountStack.size() > 1 && maxEntityCountExceeded()) {
+            return;
+        }
+
         LOG.debug("Putting '{}': '{}'", name, value);
         flattener.literal(name, value);
     }
@@ -430,6 +445,18 @@ public String getEntityMemberName() {
         return entityMemberName;
     }
 
+    public void setMaxEntityCount(final int maxEntityCount) {
+        this.maxEntityCount = maxEntityCount;
+    }
+
+    public int getMaxEntityCount() {
+        return maxEntityCount;
+    }
+
+    private boolean maxEntityCountExceeded() {
+        return maxEntityCount >= 0 && entityCount > maxEntityCount;
+    }
+
     public enum Strictness {
 
         /**