Connection to localhost:5432 refused. Check that the hostname and port are correct and that the post

pgsql有多种权限认证方式：其中有两种是password 和 md5，这两种权限认证方式的区别请自行去官网查看，不过需要提到的一点是针对这两种权限认证方式，有两种连接方式：本地连接和外部访问，如果是外部访问，则只需要提供用户名和密码即可，如果是本地访问，除了用户名和密码还需要有操作系统访问权，所以我就尝试了一下改变pgsql的登录验证方式，结果就成功连接了，在此感谢，这篇帖子，从中得出了上述有用的信息并解决了我的问题

解决办法如图：

：

全部错误日志：

org.postgresql.util.PSQLException: Connection to localhost:5432 refused. Check that the hostname and port are correct and that the postmaster is accepting TCP/IP connections.
at org.postgresql.core.v3.ConnectionFactoryImpl.openConnectionImpl(ConnectionFactoryImpl.java:265)
at org.postgresql.core.ConnectionFactory.openConnection(ConnectionFactory.java:54)
at org.postgresql.jdbc.PgConnection.<init>(PgConnection.java:218)
at org.postgresql.Driver.makeConnection(Driver.java:407)
at org.postgresql.Driver.connect(Driver.java:275)
at java.sql.DriverManager.getConnection(DriverManager.java:664)
at java.sql.DriverManager.getConnection(DriverManager.java:247)
at SelectTest.main(SelectTest.java:17)

Caused by: java.net.ConnectException: Connection refused: connect
at java.net.DualStackPlainSocketImpl.waitForConnect(Native Method)
at java.net.DualStackPlainSocketImpl.socketConnect(DualStackPlainSocketImpl.java:85)
at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:350)
at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:206)
at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:188)
at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:172)
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
at java.net.Socket.connect(Socket.java:589)
at org.postgresql.core.PGStream.<init>(PGStream.java:64)
at org.postgresql.core.v3.ConnectionFactoryImpl.openConnectionImpl(ConnectionFactoryImpl.java:147)
... 7 more

Exception in thread "main" java.lang.NullPointerException
at SelectTest.main(SelectTest.java:42)