Implemented reader (deserialization) side of #65

jr-objects/src/main/java/com/fasterxml/jackson/jr/ob/api/ValueReader.java

@@ -44,12 +44,20 @@ protected ValueReader(Class<?> valueType) {
      * Method called to deserialize value of type supported by this reader, using
      * given parser. Parser is not yet positioned to the (first) token
      * of the value to read and needs to be advanced.
+     *<p>
+     * Default implementation simply calls `p.nextToken()` first, then calls
+     * {#link {@link #read(JSONReader, JsonParser)}, but some implementations
+     * may decide to implement this differently to use (slightly) more efficient
+     * accessor in {@link JsonParser}, like {@link JsonParser#nextIntValue(int)}.
      *
      * @param reader Context object that allows calling other read methods for contained
      *     values of different types (for example for collection readers).
      * @param p Underlying parser used for reading decoded token stream
      */
-    public abstract Object readNext(JSONReader reader, JsonParser p) throws IOException;
+    public Object readNext(JSONReader reader, JsonParser p) throws IOException {
+        p.nextToken();
+        return read(reader, p);
+    }
 
     /*
     /**********************************************************************

jr-objects/src/test/java/com/fasterxml/jackson/jr/ob/impl/CustomValueHandlersTest.java

@@ -0,0 +1,90 @@
+package com.fasterxml.jackson.jr.ob.impl;
+
+import java.io.IOException;
+
+import com.fasterxml.jackson.core.JsonParser;
+import com.fasterxml.jackson.jr.ob.JSON;
+import com.fasterxml.jackson.jr.ob.JSONObjectException;
+import com.fasterxml.jackson.jr.ob.TestBase;
+import com.fasterxml.jackson.jr.ob.api.ReaderWriterProvider;
+import com.fasterxml.jackson.jr.ob.api.ValueReader;
+
+public class CustomValueHandlersTest extends TestBase
+{
+    static class CustomValue {
+        public int value;
+
+        // 2nd arg just to avoid discovery
+        public CustomValue(int v, boolean b) {
+            // and to ensure it goes through constructor, add 1
+            value = v + 1;
+        }
+    }
+
+    static class CustomValueBean {
+        public CustomValue custom;
+
+        protected CustomValueBean() { }
+        public CustomValueBean(int v) {
+            custom = new CustomValue(v, false);
+        }
+    }
+
+    static class CustomValueReader extends ValueReader {
+        public CustomValueReader() {
+            super(CustomValue.class);
+        }
+
+        @Override
+        public Object read(JSONReader reader, JsonParser p) throws IOException {
+            return new CustomValue(p.getIntValue(), true);
+        }
+
+        // Base class impl should be fine, although we'd use this for optimal
+        /*
+        @Override
+        public Object readNext(JSONReader reader, JsonParser p) throws IOException {
+            return new CustomValue(p.nextIntValue(-1), true);
+        }
+        */
+    }
+
+    static class CustomReaders extends ReaderWriterProvider {
+        @Override
+        public ValueReader findBeanReader(JSONReader readContext, Class<?> type) {
+            if (type.equals(CustomValue.class)) {
+                return new CustomValueReader();
+            }
+            return null;
+        }
+    }
+
+    /*
+    /**********************************************************************
+    /* Test methdods
+    /**********************************************************************
+     */
+
+    public void testSimpleCustomReader() throws Exception
+    {
+        // First: without handler, will fail to map
+        try {
+            JSON.std.beanFrom(CustomValue.class, "123");
+            fail("Should not pass");
+        } catch (JSONObjectException e) {
+            verifyException(e, ".CustomValue");
+            verifyException(e, "constructor to use");
+        }
+
+        // then with custom, should be fine
+        JSON json = JSON.std
+                .with(new CustomReaders());
+        CustomValue v = json.beanFrom(CustomValue.class, "123");
+        assertEquals(124, v.value);
+
+        // similarly with wrapper
+        CustomValueBean bean = json.beanFrom(CustomValueBean.class,
+                aposToQuotes("{ 'custom' : 137 }"));
+        assertEquals(138, bean.custom.value);
+    }
+}