Spring APIs returning XML instead of JSON

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I have two spring boot projects - A(Main larger project with APIs) and B(a library which is imported by A as a dependency in pom.xml)

pom.xml of project B:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.1.6.RELEASE</version>

        <relativePath /> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.b.root</groupId>
    <artifactId>b</artifactId>
    <version>0.0.1</version>
    <packaging>jar</packaging>
    <name>b</name>
    <description>Importable Jar</description>

    <properties>
        <java.version>11</java.version>
        <maven.compiler.source>1.8</maven.compiler.source>
        <maven.compiler.target>1.8</maven.compiler.target>
        <oauth2.version>2.1.1.RELEASE</oauth2.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
            <exclusions>
                <exclusion>
                    <groupId>org.springframework.boot</groupId>
                    <artifactId>spring-boot-starter-logging</artifactId>
                </exclusion>
                <!-- Removing dependency for the embedded Tomcat -->
                <exclusion>
                    <groupId>org.springframework.boot</groupId>
                    <artifactId>spring-boot-starter-tomcat</artifactId>
                </exclusion>
                <!-- End -->
            </exclusions>
        </dependency>

        <!-- asynchronous loggers -->
        <dependency>
            <groupId>com.lmax</groupId>
            <artifactId>disruptor</artifactId>
            <version>3.4.2</version>
        </dependency>

        <!-- Actuator -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-actuator</artifactId>
        </dependency>
        <!-- end -->

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-aop</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <exclusions>
                <exclusion>
                    <groupId>org.skyscreamer</groupId>
                    <artifactId>jsonassert</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
        <dependency>
            <groupId>org.springframework.security.oauth.boot</groupId>
            <artifactId>spring-security-oauth2-autoconfigure</artifactId>
            <version>${oauth2.version}</version>
        </dependency>


        <!--  docusign dependencies -->

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-log4j2</artifactId>
        </dependency>
        <dependency>
            <groupId>javax.persistence</groupId>
            <artifactId>javax.persistence-api</artifactId>
            <version>2.2</version>
        </dependency>

        <dependency>
            <groupId>com.google.code.gson</groupId>
            <artifactId>gson</artifactId>
            <version>2.8.5</version>
        </dependency>

        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-core</artifactId>
            <version>2.9.6</version>
        </dependency>
        <dependency>
            <groupId>org.freemarker</groupId>
            <artifactId>freemarker</artifactId>
        </dependency>
        <dependency>
            <groupId>commons-io</groupId>
            <artifactId>commons-io</artifactId>
            <version>2.6</version>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.dataformat</groupId>
            <artifactId>jackson-dataformat-xml</artifactId>
            <version>2.9.8</version>
        </dependency>

        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.18.10</version>
        </dependency>

        <dependency>
            <groupId>org.apache.commons</groupId>
            <artifactId>commons-lang3</artifactId>
        </dependency>
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>3.1.0</version>
            <scope>provided</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-jar-plugin</artifactId>
                <version>3.1.1</version>
                <executions>
                    <execution>
                        <goals>
                            <goal>jar</goal>
                        </goals>
                        <phase>package</phase>
                        <configuration>
                            <!--to be imported on other projects-->
                            <classifier>b-classifier</classifier>
                        </configuration>
                    </execution>
                </executions>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-surefire-plugin</artifactId>
                <version>2.5</version>
                <configuration>
                    <skipTests>false</skipTests>
                    <testFailureIgnore>true</testFailureIgnore>
                    <forkMode>once</forkMode>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <configuration>
                    <forceJavacCompilerUse>true</forceJavacCompilerUse>
                    <source>11</source>
                    <target>11</target>
                </configuration>
            </plugin>
        </plugins>
        <resources>
            <resource>
                <directory>src/main/java</directory>
                <filtering>false</filtering>
            </resource>
            <resource>
                <directory>src/main/resources</directory>
                <filtering>false</filtering>
            </resource>
            <resource>
                <directory>src/test/java</directory>
                <filtering>false</filtering>
            </resource>
        </resources>
    </build>

</project>

pom.xml of project A:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">

    <modelVersion>4.0.0</modelVersion>
    <groupId>com.a.root</groupId>
    <artifactId>a</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>a</name>
    <description>Project A</description>

    <properties>
        <java.version>11</java.version>
    </properties>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.3.1.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <dependencies>
        <!-- Springboot -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-actuator</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-jdbc</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-validation</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-websocket</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-test</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-thymeleaf</artifactId>
        </dependency>

        <!-- JUnit -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <exclusions>
                <exclusion>
                    <groupId>org.junit.vintage</groupId>
                    <artifactId>junit-vintage-engine</artifactId>
                </exclusion>
            </exclusions>
        </dependency>

        <!-- PostgreSQL -->
        <dependency>
            <groupId>org.postgresql</groupId>
            <artifactId>postgresql</artifactId>
        </dependency>

        <!-- https://mvnrepository.com/artifact/org.projectlombok/lombok -->
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.18.12</version>
            <scope>provided</scope>
        </dependency>
        <!-- https://mvnrepository.com/artifact/com.google.code.gson/gson -->
        <dependency>
            <groupId>com.google.code.gson</groupId>
            <artifactId>gson</artifactId>
            <version>2.8.5</version>
        </dependency>

        <!-- https://mvnrepository.com/artifact/org.openapitools/jackson-databind-nullable -->
        <dependency>
            <groupId>org.openapitools</groupId>
            <artifactId>jackson-databind-nullable</artifactId>
            <version>0.2.1</version>
        </dependency>

        <!-- https://mvnrepository.com/artifact/ch.qos.logback.contrib/logback-json-classic -->
        <dependency>
            <groupId>ch.qos.logback.contrib</groupId>
            <artifactId>logback-json-classic</artifactId>
            <version>0.1.5</version>
        </dependency>

        <!-- https://mvnrepository.com/artifact/ch.qos.logback.contrib/logback-jackson -->
        <dependency>
            <groupId>ch.qos.logback.contrib</groupId>
            <artifactId>logback-jackson</artifactId>
            <version>0.1.5</version>
        </dependency>

        <dependency>
            <groupId>commons-io</groupId>
            <artifactId>commons-io</artifactId>
            <version>2.7</version>
        </dependency>

        <dependency>
            <groupId>org.everit.json</groupId>
            <artifactId>org.everit.json.schema</artifactId>
            <version>1.3.0</version>
        </dependency>

        <dependency>
            <groupId>org.mapstruct</groupId>
            <artifactId>mapstruct</artifactId>
            <version>1.3.1.Final</version>
        </dependency>

        <dependency>
            <groupId>org.mapstruct</groupId>
            <artifactId>mapstruct-processor</artifactId>
            <version>1.3.1.Final</version>
        </dependency>

        <dependency>
            <groupId>com.nimbusds</groupId>
            <artifactId>nimbus-jose-jwt</artifactId>
            <version>9.0.1</version>
        </dependency>

        <dependency>
            <groupId>org.passay</groupId>
            <artifactId>passay</artifactId>
            <version>1.6.0</version>
        </dependency>

        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <scope>test</scope>
        </dependency>

        <!-- Importing library b -->
        <dependency>
            <groupId>com.b.root</groupId>
            <artifactId>b</artifactId>
            <version>0.0.1</version>
            <classifier>b-classifier</classifier>
        </dependency>

    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

There are APIs in project A that return JSON object. But in integration tests they are returning data in XML format causing them to fail. And this happens only when library B is used in A. If we remove B from A, then all tests pass.

This is the error message:

org.json.JSONException: Unparsable JSON string: <ResponseDTO>.....</ResponseDTO>

My guess is that there is some kind of conflict with dependencies of both projects. But not able to pin point which dependency exactly.

My guess is that as spring uses jackson to convert returning objects into json and there is a dependency in project B, it could have something to do with this library specifically:

    <dependency>
        <groupId>com.fasterxml.jackson.dataformat</groupId>
        <artifactId>jackson-dataformat-xml</artifactId>
        <version>2.9.8</version>
    </dependency>

But I'm not able to understand how would this affect anything. Let me know if some more information is needed.

EDIT 1: Adding code for controller:

TestDTO.java

@Data // lombok annotation
public class TestDTO {

  @JsonProperty(value = "id")
  @JsonSetter(nulls = Nulls.AS_EMPTY)
  private String id;

  @JsonProperty(value = "name")
  @JsonSetter(nulls = Nulls.AS_EMPTY)
  private String name;

}

TestController.java

@RestController
public class TestController {

  @Autowired
  private final TestService testService;

  @GetMapping("/test/:id")
  public TestDTO get(@PathVariable String id) {
    return testService.get(id);
  }

}

**EDIT 2: ** Added request response headers

Request

  HTTP Method = GET
  Request URI = /test/1
   Parameters = {}
      Headers = [Content-Type:"application/json", Content-Length:"616"]
         Body = <no character encoding set>
Session Attrs = {}

Response

       Status = 200
Error message = null
      Headers = [Content-Type:"application/xml;charset=UTF-8"]
 Content type = application/xml;charset=UTF-8
         Body = <TestDTO>...</TestDTO>
1 Answers

It might be, because Spring Boot picks up the xml-parsing lib through dependency B.

I would either define the produces attribute in your mappings or configure a WebMvcConfigurer to set json as the default type.

To do so, add a WebMvcConfigurer somewhere. Even in dependency B should be fine, if it is running in the same Spring context. This is for Spring Boot 2.4.2:

@Bean
public WebMvcConfigurer customConfigurer() {
    return new WebMvcConfigurer() {
        @Override
        public void configureContentNegotiation(ContentNegotiationConfigurer configurer) {
            configurer.defaultContentType(MediaType.APPLICATION_JSON);
        }
    };
}
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