Spring Boot Rest Controller erroring converting POJO to JSON with Jackson and Hibernate

Question

So this question has been asked several times and I see similar answers across SO and other question sites. The answers always seem to be either put Jackson dependencies in the class path or make sure that POJO classes have public getters(which I have tried but cant shake this error message off). I have a Spring Boot app hooked up to a MySQL db, I have little to no configuration because I wanted to see how far spring boot can auto config. I have a couple of spring boot starters in pom.xml, I assume they would handle the dependencies? When I test request path I get stacktrace.

No converter found for return value of type: class com.portfolio.bork.webapp.model.Project
org.springframework.http.converter.HttpMessageNotWritableException: No converter found for return value of type: class com.portfolio.bork.webapp.model.Project
    at org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodProcessor.writeWithMessageConverters(AbstractMessageConverterMethodProcessor.java:230)
    at org.springframework.web.servlet.mvc.method.annotation.RequestResponseBodyMethodProcessor.handleReturnValue(RequestResponseBodyMethodProcessor.java:181)
    at org.springframework.web.method.support.HandlerMethodReturnValueHandlerComposite.handleReturnValue(HandlerMethodReturnValueHandlerComposite.java:82)
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:124)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:879)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:793)
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1040)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:943)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006)
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:898)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:634)
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:541)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:367)
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:868)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1639)
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Thread.java:748)

and an error message in the console saying that,

.w.s.m.s.DefaultHandlerExceptionResolver : Resolved [org.springframework.http.converter.HttpMessageNotWritableException: No converter found for return value of type: class com.portfolio.bork.webapp.model.Project]
.w.s.m.s.DefaultHandlerExceptionResolver : Resolved [org.springframework.http.converter.HttpMessageNotWritableException: No converter found for return value of type: class java.util.LinkedHashMap]

Here is my pom.xml

<?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>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.2.5.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.portfolio.bork</groupId>
    <artifactId>webapp</artifactId>
    <version>01</version>
    <packaging>war</packaging>
    <name>webapp</name>
    <description>Demo project for Spring Boot</description>

    <properties>
        <java.version>1.8</java.version>
    </properties>

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

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
            <scope>runtime</scope>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-tomcat</artifactId>
            <scope>provided</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
            <!-- <exclusions>
                <exclusion>
                    <groupId>org.junit.vintage</groupId>
                    <artifactId>junit-vintage-engine</artifactId>
                </exclusion>
            </exclusions> -->
        </dependency>

        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <!-- <scope>runtime</scope> -->
        </dependency>

        <!-- for testing as of now -->
        <dependency>
            <groupId>org.apache.tomcat</groupId>
            <artifactId>tomcat-jdbc</artifactId>
            <version>8.5.27</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>2.10.3</version>
            <scope>test</scope>
        </dependency>
    </dependencies>

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

</project>

My controller:

package com.portfolio.bork.webapp.restcontroller;

import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.bind.annotation.RequestMethod;

import com.portfolio.bork.webapp.services.db.ProjectDao;
import com.portfolio.bork.webapp.model.Project;


@RestController
public class ProjectRestController {

private ProjectDao projectDao;

// get project
@RequestMapping(value = "/project/{projectId}", method = RequestMethod.GET )
public Project getProjectById( @PathVariable String projectId) {
    Long projectIdLong = Long.parseLong(projectId);
        return projectDao.getProjectById(projectIdLong);
}


// for constructor injection
public ProjectRestController(ProjectDao projectDao) {
    this.projectDao = projectDao;
}

public void setProjectDao(ProjectDao projectDao) {
    this.projectDao = projectDao;
}

}

Parent class Project.java,

package com.portfolio.bork.webapp.model;

import java.util.List;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.OneToMany;
import javax.persistence.Table;

@Entity
@Table (name = "project")
public class Project{

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column (name = "p_id")
    private Long id;
    @Column( name="p_title" )
    private String title;
    @Column( name = "p_date_modified")
    private String dateModified;
    @OneToMany(mappedBy = "project")
    private List<ContentBlock> contentBlocks;

    public Project() {
    }


    public Project(Long id, String title, String dateModified, List<ContentBlock> contentBlocks) {
        this.id = id;
        this.title = title;
        this.dateModified = dateModified;
        this.contentBlocks = contentBlocks;
    }

    public Long getId() {
        return this.id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getTitle() {
        return this.title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public String getDateModified() {
        return this.dateModified;
    }

    public void setDateModified(String dateModified) {
        this.dateModified = dateModified;
    }

    public List<ContentBlock> getContentBlocks() {
        return this.contentBlocks;
    }

    public void setContentBlocks(List<ContentBlock> contentBlocks) {
        this.contentBlocks = contentBlocks;
    }

    @Override
    public String toString() {
        return "{" +
            " id='" + getId() + "'" +
            ", title='" + getTitle() + "'" +
            ", dateModified='" + getDateModified() + "'" +
            "}";
    }


}

Child class,

package com.portfolio.bork.webapp.model;

import java.util.List;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.OneToMany;
import javax.persistence.Table;

@Entity
@Table (name = "project")
public class Project{

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column (name = "p_id")
    private Long id;
    @Column( name="p_title" )
    private String title;
    @Column( name = "p_date_modified")
    private String dateModified;
    @OneToMany(mappedBy = "project")
    private List<ContentBlock> contentBlocks;

    public Project() {
    }


    public Project(Long id, String title, String dateModified, List<ContentBlock> contentBlocks) {
        this.id = id;
        this.title = title;
        this.dateModified = dateModified;
        this.contentBlocks = contentBlocks;
    }

    public Long getId() {
        return this.id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getTitle() {
        return this.title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public String getDateModified() {
        return this.dateModified;
    }

    public void setDateModified(String dateModified) {
        this.dateModified = dateModified;
    }

    public List<ContentBlock> getContentBlocks() {
        return this.contentBlocks;
    }

    public void setContentBlocks(List<ContentBlock> contentBlocks) {
        this.contentBlocks = contentBlocks;
    }

    @Override
    public String toString() {
        return "{" +
            " id='" + getId() + "'" +
            ", title='" + getTitle() + "'" +
            ", dateModified='" + getDateModified() + "'" +
            "}";
    }


}

Answer 1

You explicitly told Maven not to include jackson-databind, which provides the converter, when you run your application, because you said it is only for test. Eliminate the entire dependency; spring-boot-starter-web will include it automatically.