SSM报错：No converter found for return value of type: class java.util.ArrayList at org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodProcessor.writeWithMessageConverter

我使用的是SSM框架,是在编写测试RESTFUL接口的时候出现，

@RequestMapping(value = "/selectAll", method = RequestMethod.GET)
    @ResponseBody
    public ResponseEntity<List<User>> selectAll() {
        List<User> users = this.userService.selectAll();
        if (null != users && users.size() > 0) {
            return ResponseEntity.ok(users);
        }
        return ResponseEntity.status(HttpStatus.NOT_FOUND).body(null);
    }

代码不是非常严谨，只是做测试。

访问：http://localhost:8081/selectAll

错误：

No converter found for return value of type: class java.util.ArrayList at org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodProcessor.writeWithMessageConverters(AbstractMessageConverterMethodProcessor.java:187) at org.s

原因：这是因为springmvc默认是没有对象转换成json的转换器的，需要手动添加jackson依赖。

解决：添加相关依赖

<!--jacson支持json-->
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-core</artifactId>
            <version>2.5.4</version>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>2.5.4</version>
        </dependency>

成功解决:

[{"username":"admin","password":"admin"},{"username":"zhanxuewei","password":"123456"}]

参考：https://www.cnblogs.com/hafiz/p/5812873.html