Handle htmx headers for @ResponseBody methods

htmx-spring-boot/src/main/java/io/github/wimdeblauwe/htmx/spring/boot/mvc/HtmxMvcAutoConfiguration.java

@@ -12,6 +12,7 @@
 import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
 import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;
 import org.springframework.web.servlet.mvc.method.annotation.ExceptionHandlerExceptionResolver;
+import org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter;
 import org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping;
 import tools.jackson.databind.json.JsonMapper;
 
@@ -29,8 +30,10 @@ public class HtmxMvcAutoConfiguration implements WebMvcRegistrations, WebMvcConf
     }
 
     @Override
-    public RequestMappingHandlerMapping getRequestMappingHandlerMapping() {
-        return new HtmxRequestMappingHandlerMapping();
+    public RequestMappingHandlerAdapter getRequestMappingHandlerAdapter() {
+        var adapter = new RequestMappingHandlerAdapter();
+        adapter.setResponseBodyAdvice(List.of(new HtmxResponseBodyAdvice(handlerMethodHandler)));
+        return adapter;
     }
 
     @Override
@@ -46,7 +49,9 @@ public void addArgumentResolvers(List<HandlerMethodArgumentResolver> resolvers)
 
     @Override
     public ExceptionHandlerExceptionResolver getExceptionHandlerExceptionResolver() {
-        return new HtmxExceptionHandlerExceptionResolver(handlerMethodHandler);
+        var resolver = new HtmxExceptionHandlerExceptionResolver(handlerMethodHandler);
+        resolver.setResponseBodyAdvice(List.of(new HtmxResponseBodyAdvice(handlerMethodHandler)));
+        return resolver;
     }
 
     @Bean

htmx-spring-boot/src/main/java/io/github/wimdeblauwe/htmx/spring/boot/mvc/HtmxResponseBodyAdvice.java

@@ -0,0 +1,43 @@
+package io.github.wimdeblauwe.htmx.spring.boot.mvc;
+
+import org.springframework.core.MethodParameter;
+import org.springframework.http.MediaType;
+import org.springframework.http.converter.HttpMessageConverter;
+import org.springframework.http.server.ServerHttpRequest;
+import org.springframework.http.server.ServerHttpResponse;
+import org.springframework.http.server.ServletServerHttpRequest;
+import org.springframework.http.server.ServletServerHttpResponse;
+import org.springframework.web.servlet.mvc.method.annotation.ResponseBodyAdvice;
+
+/**
+ * A {@link ResponseBodyAdvice} implementation that adds htmx response headers
+ * based on {@link HtmxResponse}.
+ * 
+ * @since 5.0.0
+ */
+public class HtmxResponseBodyAdvice implements ResponseBodyAdvice<Object> {
+
+    private final HtmxHandlerMethodHandler htmxHandlerMethodHandler;
+
+    public HtmxResponseBodyAdvice(HtmxHandlerMethodHandler htmxHandlerMethodHandler) {
+        this.htmxHandlerMethodHandler = htmxHandlerMethodHandler;
+    }
+
+    @Override
+    public boolean supports(MethodParameter returnType, Class<? extends HttpMessageConverter<?>> converterType) {
+        return true; // Apply to all @ResponseBody methods
+    }
+
+    @Override
+    public Object beforeBodyWrite(Object body, MethodParameter returnType, MediaType selectedContentType,
+            Class<? extends HttpMessageConverter<?>> selectedConverterType,
+            ServerHttpRequest request, ServerHttpResponse response) {
+
+        if (request instanceof ServletServerHttpRequest servletRequest
+                && response instanceof ServletServerHttpResponse servletResponse) {
+            htmxHandlerMethodHandler.handleMethodArgument(servletRequest.getServletRequest(),
+                    servletResponse.getServletResponse());
+        }
+        return body;
+    }
+}

htmx-spring-boot/src/test/java/io/github/wimdeblauwe/htmx/spring/boot/mvc/HtmxResponseBodyAdviceIT.java

@@ -0,0 +1,73 @@
+package io.github.wimdeblauwe.htmx.spring.boot.mvc;
+
+import org.junit.jupiter.api.Test;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.resttestclient.autoconfigure.AutoConfigureRestTestClient;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.context.annotation.Import;
+import org.springframework.test.web.servlet.client.RestTestClient;
+import org.springframework.web.bind.annotation.ExceptionHandler;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.RestController;
+
+@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
+@Import({ HtmxResponseBodyAdviceIT.TestRestController.class })
+@AutoConfigureRestTestClient
+public class HtmxResponseBodyAdviceIT {
+
+    @Autowired
+    RestTestClient webClient;
+
+    @Test
+    public void testTrigger() throws Exception {
+
+        get("/trigger")
+                .expectHeader()
+                .valueEquals("HX-Trigger", "trigger1,trigger2");
+    }
+
+    @Test
+    public void testExceptionHandler() throws Exception {
+
+        get("/throw-exception")
+                .expectHeader()
+                .valueEquals("HX-Retarget", "#container");
+    }
+
+    private RestTestClient.ResponseSpec get(String uri) {
+
+        return webClient
+                .get()
+                .uri(uri)
+                .exchange()
+                .expectStatus()
+                .isOk();
+    }
+
+    @RestController
+    static class TestRestController {
+
+        @GetMapping("/trigger")
+        public Object triggerResponseBody(HtmxResponse response) {
+
+            response.addTrigger("trigger1");
+            response.addTrigger("trigger2");
+            return "response";
+        }
+
+        @GetMapping("/throw-exception")
+        public Object throwException() {
+
+            throw new RuntimeException();
+        }
+
+        @ExceptionHandler(RuntimeException.class)
+        public Object handleError(RuntimeException ex, HtmxResponse htmxResponse) {
+
+            htmxResponse.setRetarget("#container");
+            return "view";
+        }
+
+    }
+
+}