找不到本地主机或 127.0.0.1

Question

A wired problem. I wrote a scala program, which would connect to a local postgresql database. This program ran fine weeks ago, but when I run it today, it throws exception:

Caused by: java.net.UnknownHostException: localhost
    at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:184)
    at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
    at java.net.Socket.connect(Socket.java:589)
    at org.postgresql.core.PGStream.<init>(PGStream.java:68)
    at org.postgresql.core.v3.ConnectionFactoryImpl.openConnectionImpl(ConnectionFactoryImpl.java:144)

I change the connection url to "127.0.0.1", it throws that

Caused by: java.net.UnknownHostException: 127.0.0.1
    at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:184)
    at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
    at java.net.Socket.connect(Socket.java:589)
    at org.postgresql.core.PGStream.<init>(PGStream.java:68)
    at org.postgresql.core.v3.ConnectionFactoryImpl.openConnectionImpl(ConnectionFactoryImpl.java:144)
    ... 16 more

In these two situations, the connection urls are:

jdbc:postgresql://localhost:5432/readinglist

jdbc:postgresql://127.0.0.1:5432/readinglist

Additional info may useful:

1. I can connect to the local postgresql database with "--host=localhost" option in shell on my computer

2. my computer is mac book air and no vm or docker is running

3. change connection url to a remote database and it runs fine

4. I run the program in IDEA as well as in the shell, both are failed to connect to the local database

5. rebooting computer not working

6. add or comment "127.0.0.1 localhost" in /etc/hosts and then rebooting not working

More info can be afford if you want.

So I want to know what will make a program can't know "localhost" or "127.0.0.1", or without knowing the real cause, what else can I do to fix it?

Answer 1

Did you happen to add a SOCKS proxy since it last worked? Look at your stack trace:

at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)

The JVM is using a SOCKS proxy and that proxy apparently can't resolve localhost. Try removing the SOCKS proxy from your network config. In my experience Java is a little flakey with SOCKS.

Answer 2

It sounds like a similar problem I just solved. It turns out that it's the ShadowsocksX-R blocking the connection between PostgreSQL and scala program. You can see if you have ShadowsocksX-R or any VPN is on.

Here is the ShadowsocksX-R version which caused problem on my Mac: screenshot of ShadowsocksX-R version