feat:string filter

core/src/main/java/io/kestra/core/runners/pebble/Extension.java

@@ -113,6 +113,7 @@ public Map<String, Filter> getFilters() {
         filters.put("sha1", new Sha1Filter());
         filters.put("sha512", new Sha512Filter());
         filters.put("md5", new Md5Filter());
+        filters.put("string", new StringFilter());
         return filters;
     }
 

core/src/main/java/io/kestra/core/runners/pebble/filters/StringFilter.java

@@ -0,0 +1,25 @@
+package io.kestra.core.runners.pebble.filters;
+
+import io.pebbletemplates.pebble.error.PebbleException;
+import io.pebbletemplates.pebble.template.EvaluationContext;
+import io.pebbletemplates.pebble.template.PebbleTemplate;
+import io.pebbletemplates.pebble.extension.Filter;
+import java.util.List;
+import java.util.Map;
+
+public class StringFilter implements Filter {
+
+    @Override
+    public Object apply(Object input, Map<String, Object> args, PebbleTemplate self, EvaluationContext context, int lineNumber) throws PebbleException {
+        if (input == null) return null;
+
+        if (input instanceof String) return input;
+
+        return input.toString();
+    }
+
+    @Override
+    public List<String> getArgumentNames() {
+        return null;
+    }
+}

core/src/test/java/io/kestra/core/runners/pebble/filters/StringFilterTest.java

@@ -0,0 +1,35 @@
+package io.kestra.core.runners.pebble.filters;
+
+import io.kestra.core.exceptions.IllegalVariableEvaluationException;
+import io.kestra.core.junit.annotations.KestraTest;
+import io.kestra.core.runners.VariableRenderer;
+import jakarta.inject.Inject;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
+import java.util.Map;
+import java.util.stream.Stream;
+
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.is;
+
+@KestraTest
+public class StringFilterTest {
+
+    @Inject
+    VariableRenderer variableRenderer;
+
+    static Stream<Arguments> source() {
+        return Stream.of(
+            Arguments.of("{{ 12.3 | string | className }}", String.class.getName()),
+            Arguments.of("{{ {\"field\":\"hello\"} | string | className }}", String.class.getName())
+        );
+    }
+
+    @ParameterizedTest
+    @MethodSource("source")
+    void run(String exp, String expected) throws IllegalVariableEvaluationException {
+        String render = variableRenderer.render(exp, Map.of());
+        assertThat(render, is(expected));
+    }
+}