From de5fdd6382691c9622e3614a96ae8ac489cf168b Mon Sep 17 00:00:00 2001
From: lunascim <luiz-augusto.nascimento@opencascade.com>
Date: Tue, 2 Jul 2024 07:11:26 +0100
Subject: [PATCH 1/3] Implemented the possibility to add custom path functions

---
 .../function/PathFunctionFactory.java         | 13 ++++++--
 .../internal/function/CustomFunctionTest.java | 33 +++++++++++++++++++
 .../internal/function/ToUpperCase.java        | 14 ++++++++
 3 files changed, 58 insertions(+), 2 deletions(-)
 create mode 100644 json-path/src/test/java/com/jayway/jsonpath/internal/function/CustomFunctionTest.java
 create mode 100644 json-path/src/test/java/com/jayway/jsonpath/internal/function/ToUpperCase.java

diff --git a/json-path/src/main/java/com/jayway/jsonpath/internal/function/PathFunctionFactory.java b/json-path/src/main/java/com/jayway/jsonpath/internal/function/PathFunctionFactory.java
index 3a31151f2..c84a6c22b 100644
--- a/json-path/src/main/java/com/jayway/jsonpath/internal/function/PathFunctionFactory.java
+++ b/json-path/src/main/java/com/jayway/jsonpath/internal/function/PathFunctionFactory.java
@@ -1,6 +1,7 @@
 package com.jayway.jsonpath.internal.function;
 
 import com.jayway.jsonpath.InvalidPathException;
+import com.jayway.jsonpath.internal.Path;
 import com.jayway.jsonpath.internal.function.json.Append;
 import com.jayway.jsonpath.internal.function.json.KeySetFunction;
 import com.jayway.jsonpath.internal.function.numeric.Average;
@@ -14,6 +15,7 @@
 import com.jayway.jsonpath.internal.function.text.Concatenate;
 import com.jayway.jsonpath.internal.function.text.Length;
 
+import java.io.InvalidClassException;
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.Map;
@@ -28,7 +30,7 @@
  */
 public class PathFunctionFactory {
 
-    public static final Map<String, Class> FUNCTIONS;
+    private static final Map<String, Class> FUNCTIONS;
 
     static {
         // New functions should be added here and ensure the name is not overridden
@@ -56,7 +58,7 @@ public class PathFunctionFactory {
         map.put("index", Index.class);
 
 
-        FUNCTIONS = Collections.unmodifiableMap(map);
+        FUNCTIONS = map;
     }
 
     /**
@@ -85,4 +87,11 @@ public static PathFunction newFunction(String name) throws InvalidPathException
             }
         }
     }
+
+    public static void addCustomFunction(String name,Class function) throws InvalidClassException {
+        if (!PathFunction.class.isAssignableFrom(function)){
+            throw new InvalidClassException("Function with name: " + name + "must be a instance of PathFunction class");
+        }
+        FUNCTIONS.put(name,function);
+    }
 }
diff --git a/json-path/src/test/java/com/jayway/jsonpath/internal/function/CustomFunctionTest.java b/json-path/src/test/java/com/jayway/jsonpath/internal/function/CustomFunctionTest.java
new file mode 100644
index 000000000..1d1dd1cc2
--- /dev/null
+++ b/json-path/src/test/java/com/jayway/jsonpath/internal/function/CustomFunctionTest.java
@@ -0,0 +1,33 @@
+package com.jayway.jsonpath.internal.function;
+
+import com.jayway.jsonpath.Configuration;
+import com.jayway.jsonpath.Configurations;
+import com.jayway.jsonpath.internal.EvaluationContext;
+import com.jayway.jsonpath.internal.PathRef;
+import org.junit.jupiter.api.Test;
+
+import java.io.InvalidClassException;
+import java.util.List;
+
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+public class CustomFunctionTest extends BaseFunctionTest {
+
+    private Configuration conf = Configurations.JSON_SMART_CONFIGURATION;
+
+    public class InvalidFunction {
+
+    }
+    @Test
+    void testAddInvalidFunction(){
+        assertThrows(InvalidClassException.class, () -> PathFunctionFactory.addCustomFunction("invalid",
+                InvalidFunction.class));
+    }
+
+    @Test
+    void testAddValidFunction(){
+       assertDoesNotThrow(()->PathFunctionFactory.addCustomFunction("toUpperCase",ToUpperCase.class));
+       verifyTextFunction(conf,"$['text'][0].toUpperCase()","A");
+    }
+}
diff --git a/json-path/src/test/java/com/jayway/jsonpath/internal/function/ToUpperCase.java b/json-path/src/test/java/com/jayway/jsonpath/internal/function/ToUpperCase.java
new file mode 100644
index 000000000..6a7c4c1ce
--- /dev/null
+++ b/json-path/src/test/java/com/jayway/jsonpath/internal/function/ToUpperCase.java
@@ -0,0 +1,14 @@
+package com.jayway.jsonpath.internal.function;
+
+import com.jayway.jsonpath.internal.EvaluationContext;
+import com.jayway.jsonpath.internal.PathRef;
+
+import java.util.List;
+
+public class ToUpperCase implements PathFunction{
+    @Override
+    public Object invoke(String currentPath, PathRef parent, Object model, EvaluationContext ctx,
+                         List<Parameter> parameters) {
+        return ((String) model).toUpperCase();
+    }
+}

From 1782b8e0ba396e99c99d2fb2724693f661c87dc1 Mon Sep 17 00:00:00 2001
From: lunascim <luiz-augusto.nascimento@opencascade.com>
Date: Mon, 3 Feb 2025 16:15:33 +0000
Subject: [PATCH 2/3] Added the validation to avoid override existent function.

---
 .../internal/function/PathFunctionFactory.java       |  5 +++--
 .../internal/function/CustomFunctionTest.java        | 12 ++++++++----
 2 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/json-path/src/main/java/com/jayway/jsonpath/internal/function/PathFunctionFactory.java b/json-path/src/main/java/com/jayway/jsonpath/internal/function/PathFunctionFactory.java
index c84a6c22b..a9f7df5f1 100644
--- a/json-path/src/main/java/com/jayway/jsonpath/internal/function/PathFunctionFactory.java
+++ b/json-path/src/main/java/com/jayway/jsonpath/internal/function/PathFunctionFactory.java
@@ -1,7 +1,6 @@
 package com.jayway.jsonpath.internal.function;
 
 import com.jayway.jsonpath.InvalidPathException;
-import com.jayway.jsonpath.internal.Path;
 import com.jayway.jsonpath.internal.function.json.Append;
 import com.jayway.jsonpath.internal.function.json.KeySetFunction;
 import com.jayway.jsonpath.internal.function.numeric.Average;
@@ -16,7 +15,6 @@
 import com.jayway.jsonpath.internal.function.text.Length;
 
 import java.io.InvalidClassException;
-import java.util.Collections;
 import java.util.HashMap;
 import java.util.Map;
 
@@ -89,6 +87,9 @@ public static PathFunction newFunction(String name) throws InvalidPathException
     }
 
     public static void addCustomFunction(String name,Class function) throws InvalidClassException {
+        if(FUNCTIONS.containsKey(name)){
+            throw new InvalidPathException("Function with name: " + name + " already exists");
+        }
         if (!PathFunction.class.isAssignableFrom(function)){
             throw new InvalidClassException("Function with name: " + name + "must be a instance of PathFunction class");
         }
diff --git a/json-path/src/test/java/com/jayway/jsonpath/internal/function/CustomFunctionTest.java b/json-path/src/test/java/com/jayway/jsonpath/internal/function/CustomFunctionTest.java
index 1d1dd1cc2..3c9593ca9 100644
--- a/json-path/src/test/java/com/jayway/jsonpath/internal/function/CustomFunctionTest.java
+++ b/json-path/src/test/java/com/jayway/jsonpath/internal/function/CustomFunctionTest.java
@@ -2,17 +2,15 @@
 
 import com.jayway.jsonpath.Configuration;
 import com.jayway.jsonpath.Configurations;
-import com.jayway.jsonpath.internal.EvaluationContext;
-import com.jayway.jsonpath.internal.PathRef;
+import com.jayway.jsonpath.InvalidPathException;
 import org.junit.jupiter.api.Test;
 
 import java.io.InvalidClassException;
-import java.util.List;
 
 import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 
-public class CustomFunctionTest extends BaseFunctionTest {
+class CustomFunctionTest extends BaseFunctionTest {
 
     private Configuration conf = Configurations.JSON_SMART_CONFIGURATION;
 
@@ -30,4 +28,10 @@ void testAddValidFunction(){
        assertDoesNotThrow(()->PathFunctionFactory.addCustomFunction("toUpperCase",ToUpperCase.class));
        verifyTextFunction(conf,"$['text'][0].toUpperCase()","A");
     }
+
+    @Test
+    void testAddExistentFunction(){
+        assertThrows(InvalidPathException.class, () -> PathFunctionFactory.addCustomFunction("avg",
+                ToUpperCase.class));
+    }
 }

From bbace61ffdb7bfa11ae0a7db84778cb9d74643a9 Mon Sep 17 00:00:00 2001
From: movabo <mb@wetransform.to>
Date: Fri, 19 Dec 2025 10:05:16 +0100
Subject: [PATCH 3/3] Make custom path functions configurable

---
 README.md                                     | 23 +++++
 .../com/jayway/jsonpath/Configuration.java    | 78 +++++++++++++--
 .../java/com/jayway/jsonpath/JsonPath.java    |  2 +-
 .../function/PassthruPathFunction.java        |  1 +
 .../function/PathFunctionFactory.java         | 98 -------------------
 .../internal/function/json/Append.java        |  2 +-
 .../function/json/KeySetFunction.java         |  2 +-
 .../function/numeric/AbstractAggregation.java |  2 +-
 .../sequence/AbstractSequenceAggregation.java |  2 +-
 .../internal/function/text/Concatenate.java   |  2 +-
 .../internal/function/text/Length.java        |  2 +-
 .../internal/path/EvaluationContextImpl.java  |  2 +
 .../internal/path/FunctionPathToken.java      | 12 ++-
 .../jsonpath/internal/path/PathCompiler.java  |  6 +-
 .../jsonpath/internal/path/PathToken.java     |  2 +-
 .../DefaultPathFunctionProvider.java          | 62 ++++++++++++
 .../pathFunction}/PathFunction.java           |  3 +-
 .../pathFunction/PathFunctionProvider.java    | 22 +++++
 .../jsonpath/CustomPathFunctionTest.java      | 44 +++++++++
 .../internal/function/CustomFunctionTest.java | 37 -------
 .../internal/function/ToUpperCase.java        | 14 ---
 21 files changed, 243 insertions(+), 175 deletions(-)
 delete mode 100644 json-path/src/main/java/com/jayway/jsonpath/internal/function/PathFunctionFactory.java
 create mode 100644 json-path/src/main/java/com/jayway/jsonpath/spi/pathFunction/DefaultPathFunctionProvider.java
 rename json-path/src/main/java/com/jayway/jsonpath/{internal/function => spi/pathFunction}/PathFunction.java (92%)
 create mode 100644 json-path/src/main/java/com/jayway/jsonpath/spi/pathFunction/PathFunctionProvider.java
 create mode 100644 json-path/src/test/java/com/jayway/jsonpath/CustomPathFunctionTest.java
 delete mode 100644 json-path/src/test/java/com/jayway/jsonpath/internal/function/CustomFunctionTest.java
 delete mode 100644 json-path/src/test/java/com/jayway/jsonpath/internal/function/ToUpperCase.java

diff --git a/README.md b/README.md
index 0c1b32a6e..28ff3e53e 100644
--- a/README.md
+++ b/README.md
@@ -514,4 +514,27 @@ CacheProvider.setCache(new Cache() {
 });
 ```
 
+### Path Function Provider SPI
+
+This SPI allows adding, overriding, and removing the path functions available in the JsonPath path.
+Therefore, change the `PathFunctionProvider` of the `Configuration`.
+
+```java
+String json = "...";
+
+Configuration conf = Configuration.defaultConfiguration().pathFunctionProvider(new DefaultPathFunctionProvider() {
+    @Override
+    public PathFunction newFunction(String name) throws InvalidPathException {
+        if (name.equals("toUpperCase")) {
+            return (currentPath, parent, model, ctx, parameters) -> ((String) model).toUpperCase();
+        }
+        
+        // Fall back to default functions
+        return super.newFunction(name);
+    }
+});
+
+JsonPath.using(conf).parse(json).read("$.store.book[0].author.toUpperCase()").toString(); // NIGEL REES
+```
+
 [![Analytics](https://ga-beacon.appspot.com/UA-54945131-1/jsonpath/index)](https://github.com/igrigorik/ga-beacon)
diff --git a/json-path/src/main/java/com/jayway/jsonpath/Configuration.java b/json-path/src/main/java/com/jayway/jsonpath/Configuration.java
index 69427e1f0..949c9c03f 100644
--- a/json-path/src/main/java/com/jayway/jsonpath/Configuration.java
+++ b/json-path/src/main/java/com/jayway/jsonpath/Configuration.java
@@ -15,8 +15,11 @@
 package com.jayway.jsonpath;
 
 import com.jayway.jsonpath.internal.DefaultsImpl;
+import com.jayway.jsonpath.spi.pathFunction.DefaultPathFunctionProvider;
+import com.jayway.jsonpath.spi.pathFunction.PathFunction;
 import com.jayway.jsonpath.spi.json.JsonProvider;
 import com.jayway.jsonpath.spi.mapper.MappingProvider;
+import com.jayway.jsonpath.spi.pathFunction.PathFunctionProvider;
 
 import java.util.*;
 
@@ -50,16 +53,19 @@ private static Defaults getEffectiveDefaults(){
     private final MappingProvider mappingProvider;
     private final Set<Option> options;
     private final Collection<EvaluationListener> evaluationListeners;
+    private final PathFunctionProvider pathFunctionProvider;
 
-    private Configuration(JsonProvider jsonProvider, MappingProvider mappingProvider, EnumSet<Option> options, Collection<EvaluationListener> evaluationListeners) {
+    private Configuration(JsonProvider jsonProvider, MappingProvider mappingProvider, EnumSet<Option> options, Collection<EvaluationListener> evaluationListeners, PathFunctionProvider pathFunctionProvider) {
         notNull(jsonProvider, "jsonProvider can not be null");
         notNull(mappingProvider, "mappingProvider can not be null");
         notNull(options, "setOptions can not be null");
         notNull(evaluationListeners, "evaluationListeners can not be null");
+        notNull(pathFunctionProvider, "pathFunctionProvider can not be null");
         this.jsonProvider = jsonProvider;
         this.mappingProvider = mappingProvider;
         this.options = Collections.unmodifiableSet(options);
         this.evaluationListeners = Collections.unmodifiableCollection(evaluationListeners);
+        this.pathFunctionProvider = pathFunctionProvider;
     }
 
     /**
@@ -68,7 +74,13 @@ private Configuration(JsonProvider jsonProvider, MappingProvider mappingProvider
      * @return a new configuration
      */
     public Configuration addEvaluationListeners(EvaluationListener... evaluationListener){
-        return Configuration.builder().jsonProvider(jsonProvider).mappingProvider(mappingProvider).options(options).evaluationListener(evaluationListener).build();
+        return Configuration.builder()
+                .jsonProvider(jsonProvider)
+                .mappingProvider(mappingProvider)
+                .options(options)
+                .evaluationListener(evaluationListener)
+                .pathFunctionProvider(pathFunctionProvider)
+                .build();
     }
 
     /**
@@ -77,7 +89,13 @@ public Configuration addEvaluationListeners(EvaluationListener... evaluationList
      * @return a new configuration
      */
     public Configuration setEvaluationListeners(EvaluationListener... evaluationListener){
-        return Configuration.builder().jsonProvider(jsonProvider).mappingProvider(mappingProvider).options(options).evaluationListener(evaluationListener).build();
+        return Configuration.builder()
+                .jsonProvider(jsonProvider)
+                .mappingProvider(mappingProvider)
+                .options(options)
+                .evaluationListener(evaluationListener)
+                .pathFunctionProvider(pathFunctionProvider)
+                .build();
     }
 
     /**
@@ -94,7 +112,13 @@ public Collection<EvaluationListener> getEvaluationListeners(){
      * @return a new configuration
      */
     public Configuration jsonProvider(JsonProvider newJsonProvider) {
-        return Configuration.builder().jsonProvider(newJsonProvider).mappingProvider(mappingProvider).options(options).evaluationListener(evaluationListeners).build();
+        return Configuration.builder()
+                .jsonProvider(newJsonProvider)
+                .mappingProvider(mappingProvider)
+                .options(options)
+                .evaluationListener(evaluationListeners)
+                .pathFunctionProvider(pathFunctionProvider)
+                .build();
     }
 
     /**
@@ -111,7 +135,13 @@ public JsonProvider jsonProvider() {
      * @return a new configuration
      */
     public Configuration mappingProvider(MappingProvider newMappingProvider) {
-        return Configuration.builder().jsonProvider(jsonProvider).mappingProvider(newMappingProvider).options(options).evaluationListener(evaluationListeners).build();
+        return Configuration.builder()
+                .jsonProvider(jsonProvider)
+                .mappingProvider(newMappingProvider)
+                .options(options)
+                .evaluationListener(evaluationListeners)
+                .pathFunctionProvider(pathFunctionProvider)
+                .build();
     }
 
     /**
@@ -122,6 +152,20 @@ public MappingProvider mappingProvider() {
         return mappingProvider;
     }
 
+    public Configuration pathFunctionProvider(PathFunctionProvider newPathFunctionProvider) {
+        return Configuration.builder()
+                .jsonProvider(jsonProvider)
+                .mappingProvider(mappingProvider)
+                .options(options)
+                .evaluationListener(evaluationListeners)
+                .pathFunctionProvider(newPathFunctionProvider)
+                .build();
+    }
+
+    public PathFunctionProvider pathFunctionProvider() {
+        return this.pathFunctionProvider;
+    }
+
     /**
      * Creates a new configuration by adding the new options to the options used in this configuration.
      * @param options options to add
@@ -131,7 +175,13 @@ public Configuration addOptions(Option... options) {
         EnumSet<Option> opts = EnumSet.noneOf(Option.class);
         opts.addAll(this.options);
         opts.addAll(asList(options));
-        return Configuration.builder().jsonProvider(jsonProvider).mappingProvider(mappingProvider).options(opts).evaluationListener(evaluationListeners).build();
+        return Configuration.builder()
+                .jsonProvider(jsonProvider)
+                .mappingProvider(mappingProvider)
+                .options(opts)
+                .evaluationListener(evaluationListeners)
+                .pathFunctionProvider(pathFunctionProvider)
+                .build();
     }
 
     /**
@@ -140,7 +190,13 @@ public Configuration addOptions(Option... options) {
      * @return the new configuration instance
      */
     public Configuration setOptions(Option... options) {
-        return Configuration.builder().jsonProvider(jsonProvider).mappingProvider(mappingProvider).options(options).evaluationListener(evaluationListeners).build();
+        return Configuration.builder()
+                .jsonProvider(jsonProvider)
+                .mappingProvider(mappingProvider)
+                .options(options)
+                .evaluationListener(evaluationListeners)
+                .pathFunctionProvider(pathFunctionProvider)
+                .build();
     }
 
     /**
@@ -186,6 +242,7 @@ public static class ConfigurationBuilder {
         private MappingProvider mappingProvider;
         private EnumSet<Option> options = EnumSet.noneOf(Option.class);
         private Collection<EvaluationListener> evaluationListener = new ArrayList<EvaluationListener>();
+        private PathFunctionProvider pathFunctionProvider = new DefaultPathFunctionProvider();
 
         public ConfigurationBuilder jsonProvider(JsonProvider provider) {
             this.jsonProvider = provider;
@@ -219,6 +276,11 @@ public ConfigurationBuilder evaluationListener(Collection<EvaluationListener> li
             return this;
         }
 
+        public ConfigurationBuilder pathFunctionProvider(PathFunctionProvider pathFunctionProvider) {
+            this.pathFunctionProvider = pathFunctionProvider;
+            return this;
+        }
+
         public Configuration build() {
             if (jsonProvider == null || mappingProvider == null) {
                 final Defaults defaults = getEffectiveDefaults();
@@ -229,7 +291,7 @@ public Configuration build() {
                     mappingProvider = defaults.mappingProvider();
                 }
             }
-            return new Configuration(jsonProvider, mappingProvider, options, evaluationListener);
+            return new Configuration(jsonProvider, mappingProvider, options, evaluationListener, pathFunctionProvider);
         }
     }
 
diff --git a/json-path/src/main/java/com/jayway/jsonpath/JsonPath.java b/json-path/src/main/java/com/jayway/jsonpath/JsonPath.java
index 01c7db03a..401166d68 100644
--- a/json-path/src/main/java/com/jayway/jsonpath/JsonPath.java
+++ b/json-path/src/main/java/com/jayway/jsonpath/JsonPath.java
@@ -18,6 +18,7 @@
 import com.jayway.jsonpath.internal.*;
 import com.jayway.jsonpath.internal.path.PathCompiler;
 import com.jayway.jsonpath.spi.json.JsonProvider;
+import com.jayway.jsonpath.spi.pathFunction.PathFunctionProvider;
 
 import java.io.File;
 import java.io.FileInputStream;
@@ -515,7 +516,6 @@ public static JsonPath compile(String jsonPath, Predicate... filters) {
         return new JsonPath(jsonPath, filters);
     }
 
-
     // --------------------------------------------------------
     //
     // Static utility functions
diff --git a/json-path/src/main/java/com/jayway/jsonpath/internal/function/PassthruPathFunction.java b/json-path/src/main/java/com/jayway/jsonpath/internal/function/PassthruPathFunction.java
index 36d7da77a..a90b27814 100644
--- a/json-path/src/main/java/com/jayway/jsonpath/internal/function/PassthruPathFunction.java
+++ b/json-path/src/main/java/com/jayway/jsonpath/internal/function/PassthruPathFunction.java
@@ -2,6 +2,7 @@
 
 import com.jayway.jsonpath.internal.EvaluationContext;
 import com.jayway.jsonpath.internal.PathRef;
+import com.jayway.jsonpath.spi.pathFunction.PathFunction;
 
 import java.util.List;
 
diff --git a/json-path/src/main/java/com/jayway/jsonpath/internal/function/PathFunctionFactory.java b/json-path/src/main/java/com/jayway/jsonpath/internal/function/PathFunctionFactory.java
deleted file mode 100644
index a9f7df5f1..000000000
--- a/json-path/src/main/java/com/jayway/jsonpath/internal/function/PathFunctionFactory.java
+++ /dev/null
@@ -1,98 +0,0 @@
-package com.jayway.jsonpath.internal.function;
-
-import com.jayway.jsonpath.InvalidPathException;
-import com.jayway.jsonpath.internal.function.json.Append;
-import com.jayway.jsonpath.internal.function.json.KeySetFunction;
-import com.jayway.jsonpath.internal.function.numeric.Average;
-import com.jayway.jsonpath.internal.function.numeric.Max;
-import com.jayway.jsonpath.internal.function.numeric.Min;
-import com.jayway.jsonpath.internal.function.numeric.StandardDeviation;
-import com.jayway.jsonpath.internal.function.numeric.Sum;
-import com.jayway.jsonpath.internal.function.sequence.First;
-import com.jayway.jsonpath.internal.function.sequence.Index;
-import com.jayway.jsonpath.internal.function.sequence.Last;
-import com.jayway.jsonpath.internal.function.text.Concatenate;
-import com.jayway.jsonpath.internal.function.text.Length;
-
-import java.io.InvalidClassException;
-import java.util.HashMap;
-import java.util.Map;
-
-/**
- * Implements a factory that given a name of the function will return the Function implementation, or null
- * if the value is not obtained.
- *
- * Leverages the function's name in order to determine which function to execute which is maintained internally
- * here via a static map
- *
- */
-public class PathFunctionFactory {
-
-    private static final Map<String, Class> FUNCTIONS;
-
-    static {
-        // New functions should be added here and ensure the name is not overridden
-        Map<String, Class> map = new HashMap<String, Class>();
-
-        // Math Functions
-        map.put("avg", Average.class);
-        map.put("stddev", StandardDeviation.class);
-        map.put("sum", Sum.class);
-        map.put("min", Min.class);
-        map.put("max", Max.class);
-
-        // Text Functions
-        map.put("concat", Concatenate.class);
-
-        // JSON Entity Functions
-        map.put(Length.TOKEN_NAME, Length.class);
-        map.put("size", Length.class);
-        map.put("append", Append.class);
-        map.put("keys", KeySetFunction.class);
-        
-        // Sequential Functions
-        map.put("first", First.class);
-        map.put("last", Last.class);
-        map.put("index", Index.class);
-
-
-        FUNCTIONS = map;
-    }
-
-    /**
-     * Returns the function by name or throws InvalidPathException if function not found.
-     *
-     * @see #FUNCTIONS
-     * @see PathFunction
-     *
-     * @param name
-     *      The name of the function
-     *
-     * @return
-     *      The implementation of a function
-     *
-     * @throws InvalidPathException
-     */
-    public static PathFunction newFunction(String name) throws InvalidPathException {
-        Class functionClazz = FUNCTIONS.get(name);
-        if(functionClazz == null){
-            throw new InvalidPathException("Function with name: " + name + " does not exist.");
-        } else {
-            try {
-                return (PathFunction)functionClazz.newInstance();
-            } catch (Exception e) {
-                throw new InvalidPathException("Function of name: " + name + " cannot be created", e);
-            }
-        }
-    }
-
-    public static void addCustomFunction(String name,Class function) throws InvalidClassException {
-        if(FUNCTIONS.containsKey(name)){
-            throw new InvalidPathException("Function with name: " + name + " already exists");
-        }
-        if (!PathFunction.class.isAssignableFrom(function)){
-            throw new InvalidClassException("Function with name: " + name + "must be a instance of PathFunction class");
-        }
-        FUNCTIONS.put(name,function);
-    }
-}
diff --git a/json-path/src/main/java/com/jayway/jsonpath/internal/function/json/Append.java b/json-path/src/main/java/com/jayway/jsonpath/internal/function/json/Append.java
index ed39d4a8b..a8c95a2cb 100644
--- a/json-path/src/main/java/com/jayway/jsonpath/internal/function/json/Append.java
+++ b/json-path/src/main/java/com/jayway/jsonpath/internal/function/json/Append.java
@@ -3,7 +3,7 @@
 import com.jayway.jsonpath.internal.EvaluationContext;
 import com.jayway.jsonpath.internal.PathRef;
 import com.jayway.jsonpath.internal.function.Parameter;
-import com.jayway.jsonpath.internal.function.PathFunction;
+import com.jayway.jsonpath.spi.pathFunction.PathFunction;
 import com.jayway.jsonpath.spi.json.JsonProvider;
 
 import java.util.List;
diff --git a/json-path/src/main/java/com/jayway/jsonpath/internal/function/json/KeySetFunction.java b/json-path/src/main/java/com/jayway/jsonpath/internal/function/json/KeySetFunction.java
index 049d6de0e..3162e3164 100644
--- a/json-path/src/main/java/com/jayway/jsonpath/internal/function/json/KeySetFunction.java
+++ b/json-path/src/main/java/com/jayway/jsonpath/internal/function/json/KeySetFunction.java
@@ -3,7 +3,7 @@
 import com.jayway.jsonpath.internal.EvaluationContext;
 import com.jayway.jsonpath.internal.PathRef;
 import com.jayway.jsonpath.internal.function.Parameter;
-import com.jayway.jsonpath.internal.function.PathFunction;
+import com.jayway.jsonpath.spi.pathFunction.PathFunction;
 
 import java.util.List;
 
diff --git a/json-path/src/main/java/com/jayway/jsonpath/internal/function/numeric/AbstractAggregation.java b/json-path/src/main/java/com/jayway/jsonpath/internal/function/numeric/AbstractAggregation.java
index cbc9f7bc9..bc44bf3a4 100644
--- a/json-path/src/main/java/com/jayway/jsonpath/internal/function/numeric/AbstractAggregation.java
+++ b/json-path/src/main/java/com/jayway/jsonpath/internal/function/numeric/AbstractAggregation.java
@@ -4,7 +4,7 @@
 import com.jayway.jsonpath.internal.EvaluationContext;
 import com.jayway.jsonpath.internal.PathRef;
 import com.jayway.jsonpath.internal.function.Parameter;
-import com.jayway.jsonpath.internal.function.PathFunction;
+import com.jayway.jsonpath.spi.pathFunction.PathFunction;
 
 import java.util.List;
 
diff --git a/json-path/src/main/java/com/jayway/jsonpath/internal/function/sequence/AbstractSequenceAggregation.java b/json-path/src/main/java/com/jayway/jsonpath/internal/function/sequence/AbstractSequenceAggregation.java
index 24c87e136..600fc792b 100644
--- a/json-path/src/main/java/com/jayway/jsonpath/internal/function/sequence/AbstractSequenceAggregation.java
+++ b/json-path/src/main/java/com/jayway/jsonpath/internal/function/sequence/AbstractSequenceAggregation.java
@@ -4,7 +4,7 @@
 import com.jayway.jsonpath.internal.EvaluationContext;
 import com.jayway.jsonpath.internal.PathRef;
 import com.jayway.jsonpath.internal.function.Parameter;
-import com.jayway.jsonpath.internal.function.PathFunction;
+import com.jayway.jsonpath.spi.pathFunction.PathFunction;
 
 import java.util.ArrayList;
 import java.util.List;
diff --git a/json-path/src/main/java/com/jayway/jsonpath/internal/function/text/Concatenate.java b/json-path/src/main/java/com/jayway/jsonpath/internal/function/text/Concatenate.java
index d499afef3..cc8e2d2dc 100644
--- a/json-path/src/main/java/com/jayway/jsonpath/internal/function/text/Concatenate.java
+++ b/json-path/src/main/java/com/jayway/jsonpath/internal/function/text/Concatenate.java
@@ -3,7 +3,7 @@
 import com.jayway.jsonpath.internal.EvaluationContext;
 import com.jayway.jsonpath.internal.PathRef;
 import com.jayway.jsonpath.internal.function.Parameter;
-import com.jayway.jsonpath.internal.function.PathFunction;
+import com.jayway.jsonpath.spi.pathFunction.PathFunction;
 
 import java.util.List;
 
diff --git a/json-path/src/main/java/com/jayway/jsonpath/internal/function/text/Length.java b/json-path/src/main/java/com/jayway/jsonpath/internal/function/text/Length.java
index ea8ab1ffe..03b973b18 100644
--- a/json-path/src/main/java/com/jayway/jsonpath/internal/function/text/Length.java
+++ b/json-path/src/main/java/com/jayway/jsonpath/internal/function/text/Length.java
@@ -4,7 +4,7 @@
 import com.jayway.jsonpath.internal.Path;
 import com.jayway.jsonpath.internal.PathRef;
 import com.jayway.jsonpath.internal.function.Parameter;
-import com.jayway.jsonpath.internal.function.PathFunction;
+import com.jayway.jsonpath.spi.pathFunction.PathFunction;
 import com.jayway.jsonpath.internal.path.CompiledPath;
 import com.jayway.jsonpath.internal.path.PathToken;
 import com.jayway.jsonpath.internal.path.RootPathToken;
diff --git a/json-path/src/main/java/com/jayway/jsonpath/internal/path/EvaluationContextImpl.java b/json-path/src/main/java/com/jayway/jsonpath/internal/path/EvaluationContextImpl.java
index d3fd0b1c6..bf8574c7d 100644
--- a/json-path/src/main/java/com/jayway/jsonpath/internal/path/EvaluationContextImpl.java
+++ b/json-path/src/main/java/com/jayway/jsonpath/internal/path/EvaluationContextImpl.java
@@ -23,6 +23,7 @@
 import com.jayway.jsonpath.internal.Path;
 import com.jayway.jsonpath.internal.PathRef;
 import com.jayway.jsonpath.spi.json.JsonProvider;
+import com.jayway.jsonpath.spi.pathFunction.PathFunctionProvider;
 
 import java.util.ArrayList;
 import java.util.Collection;
@@ -98,6 +99,7 @@ public void addResult(String path, PathRef operation, Object model) {
         }
     }
 
+    public PathFunctionProvider functionProvider() { return configuration.pathFunctionProvider(); }
 
     public JsonProvider jsonProvider() {
         return configuration.jsonProvider();
diff --git a/json-path/src/main/java/com/jayway/jsonpath/internal/path/FunctionPathToken.java b/json-path/src/main/java/com/jayway/jsonpath/internal/path/FunctionPathToken.java
index 0f4498958..592b910a9 100644
--- a/json-path/src/main/java/com/jayway/jsonpath/internal/path/FunctionPathToken.java
+++ b/json-path/src/main/java/com/jayway/jsonpath/internal/path/FunctionPathToken.java
@@ -3,17 +3,18 @@
 import com.jayway.jsonpath.internal.Path;
 import com.jayway.jsonpath.internal.PathRef;
 import com.jayway.jsonpath.internal.function.Parameter;
-import com.jayway.jsonpath.internal.function.PathFunction;
-import com.jayway.jsonpath.internal.function.PathFunctionFactory;
+import com.jayway.jsonpath.spi.pathFunction.PathFunction;
 import com.jayway.jsonpath.internal.function.latebinding.JsonLateBindingValue;
 import com.jayway.jsonpath.internal.function.latebinding.PathLateBindingValue;
+import com.jayway.jsonpath.spi.pathFunction.PathFunctionProvider;
 
 import java.util.List;
+import java.util.Map;
 
 /**
- * Token representing a Function call to one of the functions produced via the FunctionFactory
+ * Token representing a Function call to one of the functions produced via the FunctionProvider
  *
- * @see PathFunctionFactory
+ * @see PathFunctionProvider
  *
  * Created by mattg on 6/27/15.
  */
@@ -22,6 +23,7 @@ public class FunctionPathToken extends PathToken {
     private final String functionName;
     private final String pathFragment;
     private List<Parameter> functionParams;
+    private Map<String, Class<? extends PathFunction>> customFunctions;
 
     public FunctionPathToken(String pathFragment, List<Parameter> parameters) {
         this.pathFragment = pathFragment + ((parameters != null && parameters.size() > 0) ? "(...)" : "()");
@@ -36,7 +38,7 @@ public FunctionPathToken(String pathFragment, List<Parameter> parameters) {
 
     @Override
     public void evaluate(String currentPath, PathRef parent, Object model, EvaluationContextImpl ctx) {
-        PathFunction pathFunction = PathFunctionFactory.newFunction(functionName);
+        PathFunction pathFunction = ctx.functionProvider().newFunction(functionName);
         evaluateParameters(currentPath, parent, model, ctx);
         Object result = pathFunction.invoke(currentPath, parent, model, ctx, functionParams);
         ctx.addResult(currentPath + "." + functionName, parent, result);
diff --git a/json-path/src/main/java/com/jayway/jsonpath/internal/path/PathCompiler.java b/json-path/src/main/java/com/jayway/jsonpath/internal/path/PathCompiler.java
index 27b6e0633..63554668c 100644
--- a/json-path/src/main/java/com/jayway/jsonpath/internal/path/PathCompiler.java
+++ b/json-path/src/main/java/com/jayway/jsonpath/internal/path/PathCompiler.java
@@ -8,11 +8,9 @@
 import com.jayway.jsonpath.internal.filter.FilterCompiler;
 import com.jayway.jsonpath.internal.function.ParamType;
 import com.jayway.jsonpath.internal.function.Parameter;
+import com.jayway.jsonpath.spi.pathFunction.PathFunctionProvider;
 
-import java.util.ArrayList;
-import java.util.Collection;
-import java.util.LinkedList;
-import java.util.List;
+import java.util.*;
 
 import static java.lang.Character.isDigit;
 import static java.util.Arrays.asList;
diff --git a/json-path/src/main/java/com/jayway/jsonpath/internal/path/PathToken.java b/json-path/src/main/java/com/jayway/jsonpath/internal/path/PathToken.java
index 34cf1402b..1d4f158d4 100644
--- a/json-path/src/main/java/com/jayway/jsonpath/internal/path/PathToken.java
+++ b/json-path/src/main/java/com/jayway/jsonpath/internal/path/PathToken.java
@@ -18,7 +18,7 @@
 import com.jayway.jsonpath.PathNotFoundException;
 import com.jayway.jsonpath.internal.PathRef;
 import com.jayway.jsonpath.internal.Utils;
-import com.jayway.jsonpath.internal.function.PathFunction;
+import com.jayway.jsonpath.spi.pathFunction.PathFunction;
 import com.jayway.jsonpath.spi.json.JsonProvider;
 
 import java.util.List;
diff --git a/json-path/src/main/java/com/jayway/jsonpath/spi/pathFunction/DefaultPathFunctionProvider.java b/json-path/src/main/java/com/jayway/jsonpath/spi/pathFunction/DefaultPathFunctionProvider.java
new file mode 100644
index 000000000..646059efd
--- /dev/null
+++ b/json-path/src/main/java/com/jayway/jsonpath/spi/pathFunction/DefaultPathFunctionProvider.java
@@ -0,0 +1,62 @@
+package com.jayway.jsonpath.spi.pathFunction;
+
+import com.jayway.jsonpath.InvalidPathException;
+import com.jayway.jsonpath.internal.function.json.Append;
+import com.jayway.jsonpath.internal.function.json.KeySetFunction;
+import com.jayway.jsonpath.internal.function.numeric.*;
+import com.jayway.jsonpath.internal.function.sequence.First;
+import com.jayway.jsonpath.internal.function.sequence.Index;
+import com.jayway.jsonpath.internal.function.sequence.Last;
+import com.jayway.jsonpath.internal.function.text.Concatenate;
+import com.jayway.jsonpath.internal.function.text.Length;
+
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.Map;
+
+public class DefaultPathFunctionProvider implements PathFunctionProvider {
+    public static final Map<String, Class<? extends PathFunction>> DEFAULT_FUNCTIONS;
+
+    static {
+        // New functions should be added here and ensure the name is not overridden
+        Map<String, Class<? extends PathFunction>> map = new HashMap<>();
+
+        // Math Functions
+        map.put("avg", Average.class);
+        map.put("stddev", StandardDeviation.class);
+        map.put("sum", Sum.class);
+        map.put("min", Min.class);
+        map.put("max", Max.class);
+
+        // Text Functions
+        map.put("concat", Concatenate.class);
+
+        // JSON Entity Functions
+        map.put(Length.TOKEN_NAME, Length.class);
+        map.put("size", Length.class);
+        map.put("append", Append.class);
+        map.put("keys", KeySetFunction.class);
+
+        // Sequential Functions
+        map.put("first", First.class);
+        map.put("last", Last.class);
+        map.put("index", Index.class);
+
+
+        DEFAULT_FUNCTIONS = Collections.unmodifiableMap(map);
+    }
+
+    @Override
+    public PathFunction newFunction(String name) throws InvalidPathException {
+        Class<? extends PathFunction> functionClazz = DEFAULT_FUNCTIONS.get(name);
+        if(functionClazz == null){
+            throw new InvalidPathException("Function with name: " + name + " does not exist.");
+        } else {
+            try {
+                return functionClazz.getDeclaredConstructor().newInstance();
+            } catch (Exception e) {
+                throw new InvalidPathException("Function of name: " + name + " cannot be created", e);
+            }
+        }
+    }
+}
diff --git a/json-path/src/main/java/com/jayway/jsonpath/internal/function/PathFunction.java b/json-path/src/main/java/com/jayway/jsonpath/spi/pathFunction/PathFunction.java
similarity index 92%
rename from json-path/src/main/java/com/jayway/jsonpath/internal/function/PathFunction.java
rename to json-path/src/main/java/com/jayway/jsonpath/spi/pathFunction/PathFunction.java
index ac3a353ba..585c96471 100644
--- a/json-path/src/main/java/com/jayway/jsonpath/internal/function/PathFunction.java
+++ b/json-path/src/main/java/com/jayway/jsonpath/spi/pathFunction/PathFunction.java
@@ -1,7 +1,8 @@
-package com.jayway.jsonpath.internal.function;
+package com.jayway.jsonpath.spi.pathFunction;
 
 import com.jayway.jsonpath.internal.EvaluationContext;
 import com.jayway.jsonpath.internal.PathRef;
+import com.jayway.jsonpath.internal.function.Parameter;
 
 import java.util.List;
 
diff --git a/json-path/src/main/java/com/jayway/jsonpath/spi/pathFunction/PathFunctionProvider.java b/json-path/src/main/java/com/jayway/jsonpath/spi/pathFunction/PathFunctionProvider.java
new file mode 100644
index 000000000..210da9e5f
--- /dev/null
+++ b/json-path/src/main/java/com/jayway/jsonpath/spi/pathFunction/PathFunctionProvider.java
@@ -0,0 +1,22 @@
+package com.jayway.jsonpath.spi.pathFunction;
+
+import com.jayway.jsonpath.InvalidPathException;
+
+public interface PathFunctionProvider {
+
+    /**
+     * Returns the function by name or throws InvalidPathException if function not found.
+     *
+     * @see DefaultPathFunctionProvider#DEFAULT_FUNCTIONS
+     * @see PathFunction
+     *
+     * @param name
+     *      The name of the function
+     *
+     * @return
+     *      The implementation of a function
+     *
+     * @throws InvalidPathException
+     */
+    public PathFunction newFunction(String name) throws InvalidPathException;
+}
diff --git a/json-path/src/test/java/com/jayway/jsonpath/CustomPathFunctionTest.java b/json-path/src/test/java/com/jayway/jsonpath/CustomPathFunctionTest.java
new file mode 100644
index 000000000..436f3ce70
--- /dev/null
+++ b/json-path/src/test/java/com/jayway/jsonpath/CustomPathFunctionTest.java
@@ -0,0 +1,44 @@
+package com.jayway.jsonpath;
+
+import com.jayway.jsonpath.internal.function.BaseFunctionTest;
+import com.jayway.jsonpath.spi.pathFunction.DefaultPathFunctionProvider;
+import com.jayway.jsonpath.spi.pathFunction.PathFunction;
+import com.jayway.jsonpath.spi.pathFunction.PathFunctionProvider;
+import org.junit.jupiter.api.Test;
+
+import static com.jayway.jsonpath.Configurations.JSON_ORG_CONFIGURATION;
+import static com.jayway.jsonpath.JsonPath.using;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+class CustomPathFunctionTest extends BaseFunctionTest {
+
+    @Test
+    void testCustomPathFunction() {
+        Configuration conf = Configuration.defaultConfiguration().pathFunctionProvider(new DefaultPathFunctionProvider() {
+            @Override
+            public PathFunction newFunction(String name) throws InvalidPathException {
+                if (name.equals("toUpperCase")) {
+                    return (currentPath, parent, model, ctx, parameters) -> ((String) model).toUpperCase();
+                }
+                return super.newFunction(name);
+            }
+        });
+        verifyTextFunction(conf,"$['text'][0].toUpperCase()","A");
+
+        // Make sure default configuration is not being overwritten
+        assertThrows(InvalidPathException.class, () -> {
+            using(JSON_ORG_CONFIGURATION).parse(TEXT_SERIES).read("$['text'][0].toUpperCase()");
+        });
+    }
+
+    @Test
+    void removeAllPathFunctions() {
+        Configuration conf = Configuration.defaultConfiguration().pathFunctionProvider(name -> {
+            throw new InvalidPathException("No JsonPath functions allowed");
+        });
+        verifyMathFunction(JSON_ORG_CONFIGURATION, "$['empty'].length()", 0);
+        assertThrows(InvalidPathException.class, () -> {
+            using(conf).parse(NUMBER_SERIES).read("$['empty'].length()");
+        });
+    }
+}
diff --git a/json-path/src/test/java/com/jayway/jsonpath/internal/function/CustomFunctionTest.java b/json-path/src/test/java/com/jayway/jsonpath/internal/function/CustomFunctionTest.java
deleted file mode 100644
index 3c9593ca9..000000000
--- a/json-path/src/test/java/com/jayway/jsonpath/internal/function/CustomFunctionTest.java
+++ /dev/null
@@ -1,37 +0,0 @@
-package com.jayway.jsonpath.internal.function;
-
-import com.jayway.jsonpath.Configuration;
-import com.jayway.jsonpath.Configurations;
-import com.jayway.jsonpath.InvalidPathException;
-import org.junit.jupiter.api.Test;
-
-import java.io.InvalidClassException;
-
-import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
-import static org.junit.jupiter.api.Assertions.assertThrows;
-
-class CustomFunctionTest extends BaseFunctionTest {
-
-    private Configuration conf = Configurations.JSON_SMART_CONFIGURATION;
-
-    public class InvalidFunction {
-
-    }
-    @Test
-    void testAddInvalidFunction(){
-        assertThrows(InvalidClassException.class, () -> PathFunctionFactory.addCustomFunction("invalid",
-                InvalidFunction.class));
-    }
-
-    @Test
-    void testAddValidFunction(){
-       assertDoesNotThrow(()->PathFunctionFactory.addCustomFunction("toUpperCase",ToUpperCase.class));
-       verifyTextFunction(conf,"$['text'][0].toUpperCase()","A");
-    }
-
-    @Test
-    void testAddExistentFunction(){
-        assertThrows(InvalidPathException.class, () -> PathFunctionFactory.addCustomFunction("avg",
-                ToUpperCase.class));
-    }
-}
diff --git a/json-path/src/test/java/com/jayway/jsonpath/internal/function/ToUpperCase.java b/json-path/src/test/java/com/jayway/jsonpath/internal/function/ToUpperCase.java
deleted file mode 100644
index 6a7c4c1ce..000000000
--- a/json-path/src/test/java/com/jayway/jsonpath/internal/function/ToUpperCase.java
+++ /dev/null
@@ -1,14 +0,0 @@
-package com.jayway.jsonpath.internal.function;
-
-import com.jayway.jsonpath.internal.EvaluationContext;
-import com.jayway.jsonpath.internal.PathRef;
-
-import java.util.List;
-
-public class ToUpperCase implements PathFunction{
-    @Override
-    public Object invoke(String currentPath, PathRef parent, Object model, EvaluationContext ctx,
-                         List<Parameter> parameters) {
-        return ((String) model).toUpperCase();
-    }
-}