feature(index): add Solr field/fieldtype class representation IQSS#5989

The SolrFieldProperty class is used as a POJO to wrap Boolean or String
properties of Solr <field>, <fieldType> and <dynamicField> definitions.

src/main/java/edu/harvard/iq/dataverse/search/schema/SolrFieldProperty.java

@@ -0,0 +1,125 @@
+package edu.harvard.iq.dataverse.search.schema;
+
+import java.util.Objects;
+
+/**
+ * A POJO class to hold information about {@link SolrFieldType} or {@link SolrField} properties, using typed responses.
+ * This is currently Solr specific, which only allows for lots of boolean and some other properties (using String here
+ * to reduce complexity).
+ * @param <T> The factory methods will only allow for {@link Boolean} or {@link String} types.
+ */
+public class SolrFieldProperty<T> {
+
+    private final String name;
+    private final T defaultValue;
+    private T value;
+
+    private SolrFieldProperty(String name, T value, T defaultValue) {
+        this.name = name;
+        this.value = value;
+        this.defaultValue = defaultValue;
+    }
+
+    /**
+     * Method to create a property without an explicit default.
+     * @param name The name of the property
+     * @param value  The value of the property, in this case has to be typed {@link Boolean}.
+     * @return A property field
+     * @throws IllegalArgumentException if name or value is null.
+     */
+    public static SolrFieldProperty<Boolean> bool(String name, Boolean value) {
+        return bool(name, value, null);
+    }
+    /**
+     * Method to create a property with an explicit default. The value might be omitted.
+     * @param name The name of the property
+     * @param value  The value of the property, in this case has to be typed {@link Boolean}.
+     * @param defaultValue  The default value of the property when no value present, in this case has to be typed {@link Boolean}.
+     * @return A property field
+     * @throws IllegalArgumentException if name or (value AND default value) is null.
+     */
+    public static SolrFieldProperty<Boolean> bool(String name, Boolean value, Boolean defaultValue) {
+        if ( name == null )
+            throw new IllegalArgumentException("Name cannot be null.");
+        if ( value == null && defaultValue == null)
+            throw new IllegalArgumentException("Value and defaultValue cannot both be null.");
+        return new SolrFieldProperty<>(name, value, defaultValue);
+    }
+
+    /**
+     * Method to create a property without an explicit default.
+     * @param name The name of the property
+     * @param value  The value of the property, in this case has to be typed {@link String}.
+     * @return A property field
+     * @throws IllegalArgumentException if name or value is null.
+     */
+    public static SolrFieldProperty<String> string(String name, String value) {
+        return string(name, value, null);
+    }
+    /**
+     * Method to create a property with an explicit default. The value might be omitted.
+     * @param name The name of the property
+     * @param value  The value of the property, in this case has to be typed {@link String}.
+     * @param defaultValue  The default value of the property when no value present, in this case has to be typed {@link String}.
+     * @return A property field
+     * @throws IllegalArgumentException if name or (value AND default value) is null.
+     */
+    public static SolrFieldProperty<String> string(String name, String value, String defaultValue) {
+        if ( name == null )
+            throw new IllegalArgumentException("Name cannot be null.");
+        if ( value == null && defaultValue == null)
+            throw new IllegalArgumentException("Value and defaultValue cannot both be null.");
+        return new SolrFieldProperty<>(name, value, defaultValue);
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    /**
+     * Check if the value has been set (!= null).
+     * @return true if set, false if not set.
+     */
+    public boolean isSet() {
+        return value != null;
+    }
+
+    /**
+     * Return value or defaultValue. Guaranteed not to be null, as not both can be null.
+     * @return The value or the default value.
+     */
+    public T getValue() {
+        return value == null ? defaultValue : value;
+    }
+
+    /**
+     * Set the value of this property to a different value. Will not allow setting to null if
+     * no default value is present.
+     * @param value The new value (may be null)
+     * @throws IllegalArgumentException if value is null and no default was set during creation.
+     */
+    public void setValue(T value) {
+        if (value == null && defaultValue == null)
+            throw new IllegalArgumentException("Value and defaultValue cannot both be null.");
+        this.value = value;
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(name, value, defaultValue);
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) return true;
+        if (o == null || getClass() != o.getClass()) return false;
+        SolrFieldProperty<?> that = (SolrFieldProperty<?>) o;
+        // only compare the name - we want sets to contain unique properties, distinguished by their name!
+        return Objects.equals(name, that.name);
+    }
+
+    @Override
+    public String toString() {
+        return "["+name+": "+getValue().toString()+"]";
+    }
+}