android网络访问异常：android.os.NetworkOnMainThreadException

Caused by: android.os.NetworkOnMainThreadException

at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java)

at java.net.InetAddress.lookupHostByName(InetAddress.java:388)

at java.net.InetAddress.getAllByNameImpl(InetAddress.java:239)

at java.net.InetAddress.getAllByName(InetAddress.java:214)

at libcore.net.http.HttpConnection.<init>(HttpConnection.java:70)

at libcore.net.http.HttpConnection.<init>(HttpConnection.java:50)

at libcore.net.http.HttpConnection$Address.connect(HttpConnection.java:340)

at libcore.net.http.HttpConnectionPool.get(HttpConnectionPool.java:87)

at libcore.net.http.HttpConnection.connect(HttpConnection.java:128)

at libcore.net.http.HttpEngine.openSocketConnection(HttpEngine.java:315)

at libcore.net.http.HttpEngine.connect(HttpEngine.java:310)

at libcore.net.http.HttpEngine.sendSocketRequest(HttpEngine.java:289)

at libcore.net.http.HttpEngine.sendRequest(HttpEngine.java:239)

at libcore.net.http.HttpURLConnectionImpl.connect(HttpURLConnectionImpl.java:80)

在2.3的手机上运行是没有问题的，在2.3后的手机上运行就会出现此异常。

在2.3之后的android不允许在主线程中访问网络，因为访问网络是耗时操作，如果在主线程中访问网络，在网络访问慢时，用户界面会假死，造成Android not Response,为了避免这个问题，2.3之后做了限制，必须将耗时操作放在子线程中完成！！！