Include exception cause as well

Author: shadromani

CHANGELOG.md

@@ -1,6 +1,11 @@
 CHANGELOG
 =========
 
+2.1.1
+------------------
+
+* Messages for `DeserializationException` provide more detail about the involved types when an `IllegalArgumentException` is thrown.
+
 2.1.0
 ------------------
 

src/main/java/com/maxmind/db/Decoder.java

@@ -442,10 +442,10 @@ private <T> Object decodeMapIntoObject(int size, Class<T> cls)
         catch (IllegalArgumentException e){
             StringBuilder sbErrors = new StringBuilder();  
             for (String key : parameterIndexes.keySet()) {
-                int index= parameterIndexes.get(key);
-                if ( !parameters[index].getClass().isAssignableFrom( parameterTypes[index])){
-                    sbErrors.append(" argument type mismatch in " + key + " MMDB Type: "+ parameters[index].getClass().getCanonicalName()
-                    +" Java Type: " +parameterTypes[index].getCanonicalName());
+                int index = parameterIndexes.get(key);
+                if (!parameters[index].getClass().isAssignableFrom( parameterTypes[index])) {
+                    sbErrors.append(" argument type mismatch in " + key + " MMDB Type: " + parameters[index].getClass().getCanonicalName()
+                    + " Java Type: " +parameterTypes[index].getCanonicalName());
                 }              
             }
             throw new DeserializationException("Error creating object of type: " + cls.getSimpleName() + " - " + sbErrors.toString(), e);

src/main/java/com/maxmind/db/Reader.java

@@ -8,6 +8,7 @@
 import java.net.InetAddress;
 import java.nio.ByteBuffer;
 import java.util.concurrent.atomic.AtomicReference;
+import java.util.Optional;
 import java.util.concurrent.ConcurrentHashMap;
 
 /**
@@ -180,7 +181,8 @@ record = this.readNode(buffer, record, bit);
             try {
                 dataRecord = this.resolveDataPointer(buffer, record, cls);
             } catch (DeserializationException exception) {
-                throw new DeserializationException("Error getting record for IP " + ipAddress.toString(), exception);
+                String msgCause = Optional.ofNullable(exception).map(Exception::getMessage).orElse("");
+                throw new DeserializationException("Error getting record for IP " + ipAddress.toString() + " -  " + msgCause, exception);
             }
 
         }

src/test/java/com/maxmind/db/ReaderTest.java

@@ -568,10 +568,33 @@ public TestModelSubdivision(
     }
 
     @Test
-    public void testDecodeWrongTypeSubdivisions() throws IOException {
+    public void testDecodeWrongTypeWithConstructorException() throws IOException {
         this.testReader = new Reader(getFile("GeoIP2-City-Test.mmdb"));
         DeserializationException ex = assertThrows(DeserializationException.class,
-        () -> this.testReader.get( InetAddress.getByName("2.125.160.216"),TestWrongModelSubdivisions.class));
+            () -> this.testReader.get( InetAddress.getByName("2.125.160.216"),
+            TestModelSubdivisionsWithUnknownException.class));
+        
+        assertThat(ex.getMessage(), containsString("Error getting record for IP /2.125.160.216 -  Error creating object"));
+    }
+
+    static class TestModelSubdivisionsWithUnknownException {
+        List<TestModelSubdivision> subdivisions;
+
+        @MaxMindDbConstructor
+        public TestModelSubdivisionsWithUnknownException (
+            @MaxMindDbParameter(name="subdivisions")
+            List<TestModelSubdivision> subdivisions
+        ) throws Exception{
+            throw new Exception();
+        }
+    }
+
+    @Test
+    public void testDecodeWrongTypeWithWrongArguments() throws IOException {
+        this.testReader = new Reader(getFile("GeoIP2-City-Test.mmdb"));
+        DeserializationException ex = assertThrows(DeserializationException.class,
+            () -> this.testReader.get( InetAddress.getByName("2.125.160.216"),
+            TestWrongModelSubdivisions.class));
         assertThat(ex.getMessage(), containsString("Error getting record for IP"));
     }
 
@@ -807,7 +830,7 @@ public void voidTestMapKeyIsString() throws IOException {
                 TestModelInvalidMap.class
             )
         );
-        assertEquals("Error getting record for IP /2.125.160.216", ex.getMessage());
+        assertEquals("Error getting record for IP /2.125.160.216 -  Map keys must be strings.", ex.getMessage());
     }
 
     static class TestModelInvalidMap {