httpURLConnection 报错 java.net.ConnectException: localhost/127.0.0.1:8080 - Connection refused

03-20 13:56:19.120 382-393/? W/System.err: java.net.ConnectException: localhost/127.0.0.1:8080 - Connection refused

03-20 13:56:19.170 382-393/? W/System.err: at org.apache.harmony.luni.net.PlainSocketImpl.connect(PlainSocketImpl.java:207)

03-20 13:56:19.170 382-393/? W/System.err: at org.apache.harmony.luni.net.PlainSocketImpl.connect(PlainSocketImpl.java:437)

03-20 13:56:19.180 382-393/? W/System.err: at java.net.Socket.connect(Socket.java:983)

03-20 13:56:19.180 382-393/? W/System.err: at org.apache.harmony.luni.internal.net.www.protocol.http.HttpConnection.<init>(HttpConnection.java:75)

03-20 13:56:19.220 382-393/? W/System.err: at org.apache.harmony.luni.internal.net.www.protocol.http.HttpConnection.<init>(HttpConnection.java:48)

03-20 13:56:19.220 382-393/? W/System.err: at org.apache.harmony.luni.internal.net.www.protocol.http.HttpConnection$Address.connect(HttpConnection.java:322)

03-20 13:56:19.220 382-393/? W/System.err: at org.apache.harmony.luni.internal.net.www.protocol.http.HttpConnectionPool.get(HttpConnectionPool.java:89)

03-20 13:56:19.220 382-393/? W/System.err: at org.apache.harmony.luni.internal.net.www.protocol.http.HttpURLConnectionImpl.getHttpConnection(HttpURLConnectionImpl.java:285)

03-20 13:56:19.230 382-393/? W/System.err: at org.apache.harmony.luni.internal.net.www.protocol.http.HttpURLConnectionImpl.makeConnection(HttpURLConnectionImpl.java:267)

03-20 13:56:19.230 382-393/? W/System.err: at org.apache.harmony.luni.internal.net.www.protocol.http.HttpURLConnectionImpl.retrieveResponse(HttpURLConnectionImpl.java:1018)

03-20 13:56:19.230 382-393/? W/System.err: at org.apache.harmony.luni.internal.net.www.protocol.http.HttpURLConnectionImpl.getResponseCode(HttpURLConnectionImpl.java:726)

03-20 13:56:19.250 382-393/? W/System.err: at tech.androidstudio.readfileshttpurlconnection.MainActivity.run(MainActivity.java:38)

原因分析：

我在模拟器上面运行的时候localhost 就是模拟器的ip地址了，所以在请求的时候的URL 里面应该使用的是电脑的ip地址。

解决方法：

将下面的

URL url = new URL("http://localhost:8080/tomcat.png");

修改为

URL url = new URL("http://192.168.1.106:8080/tomcat.png");

package tech.androidstudio.readfileshttpurlconnection;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;

import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.ProtocolException;
import java.net.URL;

public class MainActivity extends AppCompatActivity implements Runnable {

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

Thread thread = new Thread(this);
thread.start();
}

@Override
public void run() {
try {
//TODO 这里的ip 地址一定不能使localhost 一定要是电脑的或者是正式ip地址.
//如果写成了localhost，那么就会报错java.net.ConnectException: localhost/127.0.0.1:8080 - Connection refused
//            URL url = new URL("http://localhost:8080/tomcat.png");
URL url = new URL("http://192.168.1.106:8080/tomcat.png");
HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();
httpURLConnection.setRequestMethod("GET");
httpURLConnection.setConnectTimeout(5000);
//Sets the flag indicating whether this URLConnection allows input. It cannot be set after the connection is established.
httpURLConnection.setDoInput(true);

InputStream in = null;
FileOutputStream fos = null;
if (httpURLConnection.getResponseCode() == 200) {
in = httpURLConnection.getInputStream();
//一定不能直接在FileOutputStream里面写文件名，需要添加路径
//错误的写法：fos = new FileOutputStream("a.bmp");
//下面存储到内部存储的私有的cache目录里面，注意了生成的文件名是cachea.bmp
fos = new FileOutputStream(getCacheDir().getPath()+"a.bmp");
byte[] arr = new byte[1024];
int len = 0;
while ((len = in.read(arr)) != -1) {
fos.write(arr, 0, len);
}
in.close();
fos.close();
}

} catch (MalformedURLException e) {
e.printStackTrace();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (ProtocolException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
}