转：https://blog.csdn.net/renamayu/article/details/79799208
An Error occurred while handling another error:
exception
'yiiwebHeadersAlreadySentException' with message 'Headers already sent in /xxxx/xxxx/xxx.php on line 90.' in /xxxx/xxxx/vendor/yiisoft/yii2/web/Response.php:366
Stack trace:
#0 /xxxx/xxxx/vendor/yiisoft/yii2/web/Response.php(339): yiiwebResponse->sendHeaders()
#1 /xxxx/xxxx/vendor/yiisoft/yii2/web/ErrorHandler.php(135): yiiwebResponse->send()
#2/xxxx/xxxx/vendor/yiisoft/yii2/base/ErrorHandler.php(111):
yiiwebErrorHandler->renderException(Object(yiiwebHeadersAlreadySentException))
#3 [internal function]: yiiaseErrorHandler->handleException(Object(yiiwebHeadersAlreadySentException))
#4 {main}
使用echo 输出json格式输出，结尾没有加exit导致的报错