The mysql container in the Docker bridge network cannot connect

Springboot application visits database. Error:

com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any

enter the container where the SpringBoot application is located. Myapp-in-net can ping the mysql-test container:

 ping mysql-test
    PING mysql-test (172.18.0.4): 56 data bytes
    64 bytes from 172.18.0.4: seq=0 ttl=64 time=0.308 ms
    64 bytes from 172.18.0.4: seq=1 ttl=64 time=0.186 ms

application.properties of SpringBoot (I used a multi-data source configuration so I customized the variable name):

spring.datasource.test1.driverClassName = com.mysql.jdbc.Driver
spring.datasource.test1.url = jdbc:mysql://172.18.0.4:3306/test1?useUnicode=true&characterEncoding=utf-8
spring.datasource.test1.username = root
spring.datasource.test1.password = root

this is docker network information


$ sudo docker network inspect my-net

[
    {
        "Name": "my-net",
        "Id": "9351cf7ce0dc4b2f1d7f259ed6674eeda27997b375e113648e589d9ce35939a7",
        "Created": "2018-02-17T08:45:01.476631336Z",
        "Scope": "local",
        "Driver": "bridge",
        "EnableIPv6": false,
        "IPAM": {
            "Driver": "default",
            "Options": {},
            "Config": [
                {
                    "Subnet": "172.18.0.0/16",
                    "Gateway": "172.18.0.1"
                }
            ]
        },
        "Internal": false,
        "Attachable": false,
        "Ingress": false,
        "ConfigFrom": {
            "Network": ""
        },
        "ConfigOnly": false,
        "Containers": {
            "1bc6f9393c45f7aa405eb837d33a924b4310321cca855655247e657d1697c034": {
                "Name": "redis-in-net",
                "EndpointID": "af77c4b6d91698965605a42d2d8ad05e67d2671c1ff0a03a458630e5998203f3",
                "MacAddress": "02:42:ac:12:00:02",
                "IPv4Address": "172.18.0.2/16",
                "IPv6Address": ""
            },
            "39863741c672d21a715f54788bcde08d85239613b205563eb425c66894ab01a2": {
                "Name": "busybox2",
                "EndpointID": "34ead20723641dbd5067b82f1d2ea1f5eddccf84e7eb0272b2a622a3fd85edf2",
                "MacAddress": "02:42:ac:12:00:06",
                "IPv4Address": "172.18.0.6/16",
                "IPv6Address": ""
            },
            "8cb8107bcf1a456392971eac3a3926accfe55d1ed1a428fc6d33cd1ccdeec4f5": {
                "Name": "mysql-test",
                "EndpointID": "6458537bce07ce59dad7c46175865c80622bb27346455e0945c163731081b94c",
                "MacAddress": "02:42:ac:12:00:04",
                "IPv4Address": "172.18.0.4/16",
                "IPv6Address": ""
            },
            "d90df0352762b29ea9381003dd48ec230ae916f2e1507b20d1f79648fd131c52": {
                "Name": "myapp-in-net",
                "EndpointID": "594a039bc68d31acc11d0a6988bcc75c30c84a77aa5accfa759b1e2cc89aa203",
                "MacAddress": "02:42:ac:12:00:03",
                "IPv4Address": "172.18.0.3/16",
                "IPv6Address": ""
            }
        },
        "Options": {},
        "Labels": {}
    }
]

it is strange that there is no problem of connection failure when accessing the redis container in the same network. Configuration:

spring.redis.host=172.18.0.2
-sharp Redis
spring.redis.port=6379