Github user m4rkmckenna commented on a diff in the pull request:
https://github.com/apache/brooklyn-server/pull/593#discussion_r105952999
--- Diff:
core/src/main/java/org/apache/brooklyn/util/core/xstream/ObjectWithDefaultStringImplConverter.java
---
@@ -0,0 +1,86 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.brooklyn.util.core.xstream;
+
+import org.apache.brooklyn.util.exceptions.Exceptions;
+import org.apache.brooklyn.util.javalang.Boxing;
+
+import com.thoughtworks.xstream.converters.Converter;
+import com.thoughtworks.xstream.converters.ConverterLookup;
+import com.thoughtworks.xstream.converters.MarshallingContext;
+import com.thoughtworks.xstream.converters.UnmarshallingContext;
+import com.thoughtworks.xstream.io.HierarchicalStreamReader;
+import com.thoughtworks.xstream.io.HierarchicalStreamWriter;
+
+/**
+ * A converter that delegates to {@link
ConverterLookup#lookupConverterForType(Class)}, where
+ * possible. On unmarshalling, if there is no {@code class} attribute then
it assumes that the
+ * type must be a {@link String}.
+ *
+ * This is useful if a class has its field changed from type {@link
String} to {@link Object}.
+ * The old persisted state will look like {@code <mykey>myval</mykey>},
rather than
+ * {@code <mykey class="string">myval</mykey>}.
+ *
+ * Use this converter by annotation the field with
+ * {@code @XStreamConverter(ObjectWithDefaultStringImplConverter.class)}.
One must also call
+ * {@code xstream.processAnnotations(MyClazz.class)} to ensure the
annotation is actually parsed.
+ */
+public class ObjectWithDefaultStringImplConverter implements Converter {
+ private final ConverterLookup lookup;
+ private final ClassLoader loader;
+ private final Class<?> defaultImpl = String.class;
+
+ public ObjectWithDefaultStringImplConverter(ConverterLookup lookup,
ClassLoader loader) {
+ this.lookup = lookup;
+ this.loader = loader;
+ }
+
+ @Override
+ public boolean canConvert(@SuppressWarnings("rawtypes") Class type) {
+ return true;
--- End diff --
Worth adding a comment here as to why this is hardcoded
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