【Spring】HttpMessageNotWritableException No converter found for return value of type

1.背景

Spring boot 启动报错

Failed to write HTTP message: org.springframework.http.converter.HttpMessageNotWritableException: No converter found for return value of type: class java.util.LinkedHashMap

出现以上错误，原因在于，缺少了springmvc进行json转换需要的jar包，引入对应jar依赖：

<dependency>
  <groupId>com.fasterxml.jackson.core</groupId>
  <artifactId>jackson-core</artifactId>
  <version>2.9.6</version>
</dependency>
<dependency>
  <groupId>com.fasterxml.jackson.core</groupId>
  <artifactId>jackson-annotations</artifactId>
  <version>2.9.6</version>
</dependency>
<dependency>
  <groupId>com.fasterxml.jackson.core</groupId>
  <artifactId>jackson-databind</artifactId>
  <version>2.9.6</version>
</dependency>

另外在pom文件中如果引入springboot-web依赖排除掉了springboot-web自带的json也会导致上面的异常信息：

<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
  <exclusions>
    <exclusion>
	  <artifactId>spring-boot-starter-json</artifactId>
	  <groupId>org.springframework.boot</groupId>
	</exclusion>
  </exclusions>
</dependency>

此时，需要将依赖改为以下即可：

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

https://blog.csdn.net/cnd2449294059/article/details/104216291