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

Question

所以这个问题已经被问过好几次了，我在 SO 和其他问题网站上看到了类似的答案。 答案似乎总是将 Jackson 依赖项放在 class 路径中，或者确保 POJO 类具有公共 getter（我已经尝试过但无法摆脱此错误消息）。 我有一个 Spring 引导应用程序连接到 MySQL 数据库，我几乎没有配置，因为我想看看 spring 引导可以自动配置多远。 我在 pom.xml 中有几个 spring 启动器，我假设他们会处理依赖关系？ 当我测试请求路径时，我得到了堆栈跟踪。

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)

并在控制台中显示一条错误消息，

.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]

这是我的 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>

我的 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;
}

}

父 class 项目.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() + "'" +
            "}";
    }


}

儿童 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

您明确告诉 Maven 在运行应用程序时不要包含提供转换器的jackson-databind ，因为您说它仅用于test 。 消除整个依赖； spring-boot-starter-web将自动包含它。