java.lang.IllegalStateException: Already connected

引用\[1\]:在调试程序bug的过程中，出现了java.lang.IllegalStateException: Already connected的异常。这个异常的主要原因有两种。一种是将connection.setInput()放在了connection.connect()的后面，另一种是在get请求中设置了connection.DoOutput()。\[1\]引用\[3\]:在查看了一些RequestProperties相关的方法后，发现在判断connected是否为true的时候，会导致java.lang.IllegalStateException: Already connected异常的出现。\[3\]

这个异常的解决方法有几种。首先，确保在调用connection.connect()之前设置connection.setInput()。其次，如果是在get请求中，不要设置connection.DoOutput()。最后，可以尝试关闭防火墙，因为有时候防火墙的设置可能会导致这个异常的出现。在Linux下关闭防火墙的命令是service iptables stop。\[2\]
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