BAEL-7676: Get the Response Body in Spring Boot Filter (#16186)

spring-boot-modules/spring-boot-basic-customization-3/src/main/java/com/baeldung/responsebody/FilterConfig.java

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+package com.baeldung.responsebody;
+
+import org.springframework.boot.web.servlet.FilterRegistrationBean;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+
+@Configuration
+public class FilterConfig {
+
+    @Bean
+    public FilterRegistrationBean<MD5Filter> loggingFilter() {
+        FilterRegistrationBean<MD5Filter> registrationBean = new FilterRegistrationBean<>();
+        registrationBean.setFilter(new MD5Filter());
+        return registrationBean;
+    }
+}

spring-boot-modules/spring-boot-basic-customization-3/src/main/java/com/baeldung/responsebody/HelloWorldController.java

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+package com.baeldung.responsebody;
+
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.bind.annotation.RestController;
+
+@RestController
+@RequestMapping("/api/example")
+public class HelloWorldController {
+
+    @GetMapping
+    public String getExample() {
+        return "Hello, World!";
+    }
+}

spring-boot-modules/spring-boot-basic-customization-3/src/main/java/com/baeldung/responsebody/MD5Filter.java

@@ -0,0 +1,39 @@
+package com.baeldung.responsebody;
+
+import java.io.IOException;
+import java.security.MessageDigest;
+import java.security.NoSuchAlgorithmException;
+import java.util.logging.Logger;
+
+import org.springframework.stereotype.Component;
+import org.springframework.web.util.ContentCachingResponseWrapper;
+
+import jakarta.servlet.Filter;
+import jakarta.servlet.FilterChain;
+import jakarta.servlet.ServletException;
+import jakarta.servlet.ServletRequest;
+import jakarta.servlet.ServletResponse;
+import jakarta.servlet.http.HttpServletResponse;
+import jakarta.xml.bind.DatatypeConverter;
+
+@Component
+public class MD5Filter implements Filter {
+
+    @Override
+    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
+        ContentCachingResponseWrapper responseCacheWrapperObject = new ContentCachingResponseWrapper((HttpServletResponse) servletResponse);
+        filterChain.doFilter(servletRequest, responseCacheWrapperObject);
+
+        byte[] responseBody = responseCacheWrapperObject.getContentAsByteArray();
+
+        try {
+            MessageDigest md5Digest = MessageDigest.getInstance("MD5");
+            byte[] md5Hash = md5Digest.digest(responseBody);
+            String md5HashString = DatatypeConverter.printHexBinary(md5Hash);
+            responseCacheWrapperObject.setHeader("Response-Body-MD5", md5HashString);
+        } catch (NoSuchAlgorithmException e) {
+            throw new RuntimeException(e);
+        }
+        responseCacheWrapperObject.copyBodyToResponse();
+    }
+}

spring-boot-modules/spring-boot-basic-customization-3/src/main/java/com/baeldung/responsebody/ResponseBodyApplication.java

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+package com.baeldung.responsebody;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+
+@SpringBootApplication(scanBasePackages = "com.baeldung.responsebody")
+public class ResponseBodyApplication {
+
+    public static void main(String[] args) {
+        SpringApplication.run(ResponseBodyApplication.class, args);
+    }
+}

spring-boot-modules/spring-boot-basic-customization-3/src/test/java/com/baeldung/responsebody/ResponseBodyUnitTest.java

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+package com.baeldung.responsebody;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
+import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;
+
+import java.nio.charset.StandardCharsets;
+import java.security.MessageDigest;
+import java.security.NoSuchAlgorithmException;
+
+import org.junit.jupiter.api.Test;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.autoconfigure.web.servlet.AutoConfigureMockMvc;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.http.MediaType;
+import org.springframework.test.web.servlet.MockMvc;
+import org.springframework.test.web.servlet.MvcResult;
+
+import jakarta.xml.bind.DatatypeConverter;
+
+@SpringBootTest(classes = ResponseBodyApplication.class)
+@AutoConfigureMockMvc
+class ResponseBodyUnitTest {
+
+    @Autowired
+    private MockMvc mockMvc;
+
+    @Test
+    void whenExampleApiCallThenResponseHasMd5Header() throws Exception {
+        String endpoint = "/api/example";
+        String expectedResponse = "Hello, World!";
+        String expectedMD5 = getMD5Hash(expectedResponse);
+
+        MvcResult mvcResult = mockMvc.perform(get(endpoint).accept(MediaType.TEXT_PLAIN_VALUE))
+            .andExpect(status().isOk())
+            .andReturn();
+
+        String md5Header = mvcResult.getResponse()
+            .getHeader("Response-Body-MD5");
+        assertThat(md5Header).isEqualTo(expectedMD5);
+    }
+
+    private String getMD5Hash(String input) throws NoSuchAlgorithmException {
+        MessageDigest md5Digest = MessageDigest.getInstance("MD5");
+        byte[] md5Hash = md5Digest.digest(input.getBytes(StandardCharsets.UTF_8));
+        return DatatypeConverter.printHexBinary(md5Hash);
+    }
+}