Added first filter and join filter

src/main/java/com/mitchellbosecke/pebble/extension/core/CoreExtension.java

@@ -118,6 +118,7 @@ public Map<String, Filter> getFilters() {
         filters.put("date", new DateFilter());
         filters.put("default", new DefaultFilter());
         filters.put("first", new FirstFilter());
+        filters.put("join", new JoinFilter());
         filters.put("lower", new LowerFilter());
         filters.put("numberformat", new NumberFormatFilter());
         filters.put("sort", new SortFilter());

src/main/java/com/mitchellbosecke/pebble/extension/core/FirstFilter.java

@@ -8,7 +8,6 @@
  ******************************************************************************/
 package com.mitchellbosecke.pebble.extension.core;
 
-import java.util.ArrayList;
 import java.util.Collection;
 import java.util.List;
 import java.util.Map;
@@ -25,9 +24,7 @@ public class FirstFilter implements Filter {
 
     @Override
     public List<String> getArgumentNames() {
-        List<String> names = new ArrayList<>();
-        names.add("collection");
-        return names;
+        return null;
     }
 
     @Override

src/main/java/com/mitchellbosecke/pebble/extension/core/JoinFilter.java

@@ -0,0 +1,62 @@
+/*******************************************************************************
+ * This file is part of Pebble.
+ * 
+ * Copyright (c) 2014 by Mitchell Bösecke
+ * 
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ ******************************************************************************/
+package com.mitchellbosecke.pebble.extension.core;
+
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.List;
+import java.util.Map;
+
+import com.mitchellbosecke.pebble.extension.Filter;
+
+/**
+ * Concatenates all entries of a collection, optionally glued together
+ * with a particular character such as a comma.
+ * 
+ * @author mbosecke
+ *
+ */
+public class JoinFilter implements Filter {
+
+    @Override
+    public List<String> getArgumentNames() {
+        List<String> names = new ArrayList<>();
+        names.add("glue");
+        return names;
+    }
+
+    @Override
+    public Object apply(Object input, Map<String, Object> args) {
+        if (input == null) {
+            return null;
+        }
+
+        @SuppressWarnings("unchecked")
+        Collection<Object> inputCollection = (Collection<Object>) input;
+
+        StringBuilder builder = new StringBuilder();
+
+        String glue = null;
+        if(args.containsKey("glue")){
+            glue = (String)args.get("glue");
+        }
+
+        boolean isFirst = true;
+        for(Object entry : inputCollection){
+
+            if(!isFirst && glue != null){
+                builder.append(glue);
+            }
+            builder.append(entry);
+
+            isFirst = false;
+        }
+        return builder.toString();
+    }
+}

src/test/java/com/mitchellbosecke/pebble/CoreFiltersTest.java

@@ -476,6 +476,84 @@ public void testFirstWithStringInput() throws PebbleException, IOException {
         template.evaluate(writer, context);
         assertEquals("A", writer.toString());
     }
+
+    @Test
+    public void testJoin() throws PebbleException, IOException {
+        Loader loader = new StringLoader();
+        PebbleEngine pebble = new PebbleEngine(loader);
+
+        PebbleTemplate template = pebble
+                .getTemplate("{{ names | join(',') }}");
+
+        List<String> names = new ArrayList<>();
+        names.add("Alex");
+        names.add("Joe");
+        names.add("Bob");
+
+        Map<String, Object> context = new HashMap<>();
+        context.put("names", names);
+
+        Writer writer = new StringWriter();
+        template.evaluate(writer, context);
+        assertEquals("Alex,Joe,Bob", writer.toString());
+    }
+
+
+    @Test
+    public void testJoinWithoutGlue() throws PebbleException, IOException {
+        Loader loader = new StringLoader();
+        PebbleEngine pebble = new PebbleEngine(loader);
+
+        PebbleTemplate template = pebble
+                .getTemplate("{{ names | join }}");
+
+        List<String> names = new ArrayList<>();
+        names.add("Alex");
+        names.add("Joe");
+        names.add("Bob");
+
+        Map<String, Object> context = new HashMap<>();
+        context.put("names", names);
+
+        Writer writer = new StringWriter();
+        template.evaluate(writer, context);
+        assertEquals("AlexJoeBob", writer.toString());
+    }
+
+
+    @Test
+    public void testJoinWithNumbers() throws PebbleException, IOException {
+        Loader loader = new StringLoader();
+        PebbleEngine pebble = new PebbleEngine(loader);
+
+        PebbleTemplate template = pebble
+                .getTemplate("{{ numbers | join(',') }}");
+
+        List<Integer> numbers = new ArrayList<>();
+        numbers.add(1);
+        numbers.add(2);
+        numbers.add(3);
+
+        Map<String, Object> context = new HashMap<>();
+        context.put("numbers", numbers);
+
+        Writer writer = new StringWriter();
+        template.evaluate(writer, context);
+        assertEquals("1,2,3", writer.toString());
+    }
+
+    @Test
+    public void testJoinWithNullInput() throws PebbleException, IOException {
+        Loader loader = new StringLoader();
+        PebbleEngine pebble = new PebbleEngine(loader);
+
+        PebbleTemplate template = pebble
+                .getTemplate("{{ null | join(',') }}");
+
+        Writer writer = new StringWriter();
+        template.evaluate(writer);
+        assertEquals("", writer.toString());
+    }
 
     public class User {