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.(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.(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();
        }
    }
}