我在本地跑了一个 Tomcat ，我想在 Android 模拟器中直接通过下面的 url 地址访问 Tomcat 上的服务
http://192.168.0.20:8080/getweather
但是报错信息说 host is unresolved
我在模拟器上的浏览器上打开相同的地址，提示 page not found
请问我如何才能在模拟器上访问本机的web服务呢？
Android 模拟器是一个虚拟路由，其内部的网络跟你本机网络是不同的。
但这个路由是本机网络中的一部分，因此你可以通过 10.0.2.2 来访问本机网络服务
你上述的 URL 地址改成：http://10.0.2.2:8080/getweather 应该就好了。
Android 的文档中 Emulator Networking 有介绍到这个。
需要用 10.0.2.2 这个IP来访问本机网络
Emulator Networking
The emulator provides versatile networking capabilities that you can use to set up complex modeling and testing environments for your application. The sections below introduce the emulator's network architecture and capabilities.
Network Address Space
Each instance of the emulator runs behind a virtual router/firewall service that isolates it from your development machine's network interfaces and settings and from the internet. An emulated device can not see your development machine or other emulator instances on the network. Instead, it sees only that it is connected through Ethernet to a router/firewall.
The virtual router for each instance manages the 10.0.2/24 network address space — all addresses managed by the router are in the form of 10.0.2.<xx>, where <xx> is a number. Addresses within this space are pre-allocated by the emulator/router as follows:
| Network Address | Description |
|---|---|
| 10.0.2.1 | Router/gateway address |
| 10.0.2.2 | Special alias to your host loopback interface (i.e., 127.0.0.1 on your development machine) |
| 10.0.2.3 | First DNS server |
| 10.0.2.4 / 10.0.2.5 / 10.0.2.6 | Optional second, third and fourth DNS server (if any) |
| 10.0.2.15 | The emulated device's own network/ethernet interface |
| 127.0.0.1 | The emulated device's own loopback interface |
Note that the same address assignments are used by all running emulator instances. That means that if you have two instances running concurrently on your machine, each will have its own router and, behind that, each will have an IP address of 10.0.2.15. The instances are isolated by a router and cannot see each other on the same network. For information about how to let emulator instances communicate over TCP/UDP, see Connecting Emulator Instances.
Also note that the address 127.0.0.1 on your development machine corresponds to the emulator's own loopback interface. If you want to access services running on your development machine's loopback interface (a.k.a. 127.0.0.1 on your machine), you should use the special address 10.0.2.2 instead.
Finally, note that each emulated device's pre-allocated addresses are specific to the Android emulator and will probably be very different on real devices (which are also very likely to be NAT-ed, i.e., behind a router/firewall)