Modified the logic in setPropertyDatasource which determines if a new converter is needed (#11863)

The previous logic had two flaws
* It allowed converter model type to be a sub type of the model type but not vice versa. Similarly for presentation type.
* If the user has set a converter it should be used and not be replaced unless it is absolutely sure that it cannot in any possible way handle conversion (e.g. converter from integer to double cannot handle string to list conversion). If there is a slight chance that it can handle conversion, let it be and let the user set another converter when needed.

Change-Id: I2e1c0b3aac90be63ddbc780195f8428398e28ada

1 files changed, 46 insertions, 4 deletions

diff --git a/server/src/com/vaadin/data/util/converter/ConverterUtil.java b/server/src/com/vaadin/data/util/converter/ConverterUtil.java
index 61d155bc9a..08d7363084 100644
--- a/server/src/com/vaadin/data/util/converter/ConverterUtil.java
+++ b/server/src/com/vaadin/data/util/converter/ConverterUtil.java
@@ -151,10 +151,14 @@ public class ConverterUtil implements Serializable {
 
     /**
      * Checks if the given converter can handle conversion between the given
-     * presentation and model type
+     * presentation and model type. Does strict type checking and only returns
+     * true if the converter claims it can handle exactly the given types.
+     * 
+     * @see #canConverterPossiblyHandle(Converter, Class, Class)
      * 
      * @param converter
-     *            The converter to check
+     *            The converter to check. If this is null the result is always
+     *            false.
      * @param presentationType
      *            The presentation type
      * @param modelType
@@ -168,10 +172,48 @@ public class ConverterUtil implements Serializable {
             return false;
         }
 
-        if (!modelType.isAssignableFrom(converter.getModelType())) {
+        if (modelType != converter.getModelType()) {
+            return false;
+        }
+        if (presentationType != converter.getPresentationType()) {
             return false;
         }
-        if (!presentationType.isAssignableFrom(converter.getPresentationType())) {
+
+        return true;
+    }
+
+    /**
+     * Checks if it possible that the given converter can handle conversion
+     * between the given presentation and model type somehow.
+     * 
+     * @param converter
+     *            The converter to check. If this is null the result is always
+     *            false.
+     * @param presentationType
+     *            The presentation type
+     * @param modelType
+     *            The model type
+     * @return true if the converter possibly support conversion between the
+     *         given presentation and model type, false otherwise
+     */
+    public static boolean canConverterPossiblyHandle(Converter<?, ?> converter,
+            Class<?> presentationType, Class<?> modelType) {
+        if (converter == null) {
+            return false;
+        }
+        Class<?> converterModelType = converter.getModelType();
+
+        if (!modelType.isAssignableFrom(converterModelType)
+                && !converterModelType.isAssignableFrom(modelType)) {
+            // model types are not compatible in any way
+            return false;
+        }
+
+        Class<?> converterPresentationType = converter.getPresentationType();
+        if (!presentationType.isAssignableFrom(converterPresentationType)
+                && !converterPresentationType
+                        .isAssignableFrom(presentationType)) {
+            // presentation types are not compatible in any way
             return false;
         }