Initial thoughts on how to allow type conversion to be extensible

yahoo · Mar 10, 2017 · 60fc665 · 60fc665
1 parent db25820
commit 60fc665
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Showing 2 changed files with 72 additions and 38 deletions.
diff --git a/elide-core/src/main/java/com/yahoo/elide/utils/coerce/CoerceUtil.java b/elide-core/src/main/java/com/yahoo/elide/utils/coerce/CoerceUtil.java
@@ -7,28 +7,16 @@
 
 import com.yahoo.elide.core.exceptions.InvalidAttributeException;
 import com.yahoo.elide.core.exceptions.InvalidValueException;
-import com.yahoo.elide.utils.coerce.converters.EpochToDateConverter;
-import com.yahoo.elide.utils.coerce.converters.FromMapConverter;
-import com.yahoo.elide.utils.coerce.converters.ToEnumConverter;
+import com.yahoo.elide.utils.coerce.converters.ElideConverter;
 import org.apache.commons.beanutils.BeanUtilsBean;
 import org.apache.commons.beanutils.ConversionException;
 import org.apache.commons.beanutils.ConvertUtils;
-import org.apache.commons.beanutils.ConvertUtilsBean;
-import org.apache.commons.beanutils.Converter;
-import org.apache.commons.lang3.ClassUtils;
-
-import java.util.Date;
-import java.util.Map;
 
 /**
  * Class for coercing a value to a target class.
  */
 public class CoerceUtil {
 
-    private static final ToEnumConverter TO_ENUM_CONVERTER = new ToEnumConverter();
-    private static final FromMapConverter FROM_MAP_CONVERTER = new FromMapConverter();
-    private static final EpochToDateConverter EPOCH_TO_DATE_CONVERTER = new EpochToDateConverter();
-
     //static block for setup and registering new converters
     static {
         setup();
@@ -57,30 +45,6 @@ public static <T> T coerce(Object value, Class<T> cls) {
      * Perform CoerceUtil setup.
      */
     private static void setup() {
-        BeanUtilsBean.setInstance(new BeanUtilsBean(new ConvertUtilsBean() {
-            {
-                // https://github.com/yahoo/elide/issues/260
-                // enable throwing exceptions when conversion fails
-                register(true, false, 0);
-            }
-
-            @Override
-            /*
-             * Overriding lookup to execute enum converter if target is enum
-             * or map convert if source is map
-             */
-            public Converter lookup(Class<?> sourceType, Class<?> targetType) {
-                if (targetType.isEnum()) {
-                    return TO_ENUM_CONVERTER;
-                } else if (Map.class.isAssignableFrom(sourceType)) {
-                    return FROM_MAP_CONVERTER;
-                } else if ((String.class.isAssignableFrom(sourceType) || Number.class.isAssignableFrom(sourceType))
-                        && ClassUtils.isAssignable(targetType, Date.class)) {
-                    return EPOCH_TO_DATE_CONVERTER;
-                } else {
-                    return super.lookup(sourceType, targetType);
-                }
-            }
-        }));
+        BeanUtilsBean.setInstance(new BeanUtilsBean(new ElideConverter()));
     }
 }
diff --git a/elide-core/src/main/java/com/yahoo/elide/utils/coerce/converters/ElideConverter.java b/elide-core/src/main/java/com/yahoo/elide/utils/coerce/converters/ElideConverter.java
@@ -0,0 +1,70 @@
+/*
+ * Copyright 2017, Yahoo Inc.
+ * Licensed under the Apache License, Version 2.0
+ * See LICENSE file in project root for terms.
+ */
+
+package com.yahoo.elide.utils.coerce.converters;
+
+import org.apache.commons.beanutils.ConvertUtilsBean;
+import org.apache.commons.beanutils.Converter;
+import org.apache.commons.lang3.ClassUtils;
+
+import java.util.Date;
+import java.util.LinkedHashMap;
+import java.util.Map;
+import java.util.function.BiFunction;
+
+/**
+ * A class that knows how to convert thing to other (different) things.
+ */
+public class ElideConverter extends ConvertUtilsBean {
+    private static final ToEnumConverter TO_ENUM_CONVERTER = new ToEnumConverter();
+    private static final FromMapConverter FROM_MAP_CONVERTER = new FromMapConverter();
+    private static final EpochToDateConverter EPOCH_TO_DATE_CONVERTER = new EpochToDateConverter();
+
+    private LinkedHashMap<BiFunction<Class<?>, Class<?>, Boolean>, Converter> converters;
+
+    /**
+     * Create a new ElideConverter with a set of converters.
+     *
+     * @param converters extra converters to consider before the default converters fire
+     */
+    public ElideConverter(LinkedHashMap<BiFunction<Class<?>, Class<?>, Boolean>, Converter> converters) {
+        // yahoo/elide#260 - enable throwing exceptions when conversion fails
+        register(true, false, 0);
+        this.converters = converters;
+    }
+
+    /**
+     * Create a new ElideConverter with the default set of converters.
+     */
+    public ElideConverter() {
+        this(defaultConverters());
+    }
+
+    @Override
+    /*
+     * Overriding lookup to execute enum converter if target is enum
+     * or map convert if source is map
+     */
+    public Converter lookup(Class<?> sourceType, Class<?> targetType) {
+        for (Map.Entry<BiFunction<Class<?>, Class<?>, Boolean>, Converter> entry : converters.entrySet()) {
+            if (entry.getKey().apply(sourceType, targetType)) {
+                return entry.getValue();
+            }
+        }
+        return super.lookup(sourceType, targetType);
+    }
+
+    public static LinkedHashMap<BiFunction<Class<?>, Class<?>, Boolean>, Converter> defaultConverters() {
+        LinkedHashMap<BiFunction<Class<?>, Class<?>, Boolean>, Converter> converters = new LinkedHashMap<>();
+        converters.put((source, target) -> target.isEnum(), TO_ENUM_CONVERTER);
+        converters.put((source, target) -> Map.class.isAssignableFrom(source), FROM_MAP_CONVERTER);
+        converters.put(
+                (source, target) -> (String.class.isAssignableFrom(source) || Number.class.isAssignableFrom(source))
+                        && ClassUtils.isAssignable(target, Date.class),
+                EPOCH_TO_DATE_CONVERTER);
+        return converters;
+    }
+}