java - 使用 spring-boot : Content Negotiation failed! 未找到类型返回值的转换器

Question

我正在尝试使用 spring-boot 2.1.9 和 spring REST 在浏览器上以 JSON 格式获取 java POJO 的内容。非常基本的例子!但我得到了这篇文章标题上显示的异常(exception)情况。当我使用 @XmlRootElement 注释 POJO 类时，我在浏览器上获取 XML 内容。但是当我尝试在浏览器上获取 POJO 列表时，我得到与 JSON 相同的错误。为什么内容协商对 XML 部分有效，而对 JSON 完全无效？感谢您的每一个回答。

Whitelabel Error Page

This application has no explicit mapping for /error, so you are seeing this as a fallback.
Thu Oct 03 15:17:06 CEST 2019
There was an unexpected error (type=Internal Server Error, status=500).
No converter found for return value of type: class com.mayo.vina.restapi4.domain.Limit
org.springframework.http.converter.HttpMessageNotWritableException: No converter found for return value of type: class com.mayo.vina.restapi4.domain.Limit
    at org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodProcessor.writeWithMessageConverters(AbstractMessageConverterMethodProcessor.java:234)
    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:123)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:893)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:798)
    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)

我已经尝试过 Stackoverflow 中提供的所有答案。使用 jackson-databind 扩展 POM 文件，使用 @ResponseBody、@GetMapping 而不是 @RequestMapping，使用 Produce = "application/json"... 没有什么对我有用。

package com.mayo.vina.restapi4;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class Restapi4Application {

    public static void main(String[] args) {
        SpringApplication.run(Restapi4Application.class, args);
    }

}
-------------------------------------------------------------------------
package com.mayo.vina.restapi4.controller;

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

import com.mayo.vina.restapi4.domain.Limit;

@RestController
public class LimitController
{

    @RequestMapping("/limit")
    public Limit limit()
    {
        return new Limit(1, 10000);
    }
}
---------------------------------------------------------------------------
package com.mayo.vina.restapi4.domain;

//@XmlRootElement
public class Limit
{
    private int minimum;
    private int maximum;

    public Limit()
    {
    }

    public Limit(int minimum, int maximum)
    {
        this.minimum = minimum;
        this.maximum = maximum;
    }

    public int getMinimum()
    {
        return minimum;
    }

    public void setMinimum(int minimum)
    {
        this.minimum = minimum;
    }

    public int getMaximum()
    {
        return maximum;
    }

    public void setMaximum(int maximum)
    {
        this.maximum = maximum;
    }
}
--------------------------------------------------------------------------

<?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>2.1.9.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.mayo.vina</groupId>
    <artifactId>restapi4</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>restapi4</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-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-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

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

</project>

Answer 1

以下解决了我的问题:

所以，是的，只是重申一下，进入我的 Maven 存储库并删除 fastxml 文件夹并重新运行 Maven 就解决了我的问题。