<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
 xmlns:tools="http://schemas.android.com/tools"
 android:id="@+id/activity_main"
 android:layout_width="match_parent"
 android:layout_height="match_parent"
 android:paddingBottom="@dimen/activity_vertical_margin"
 android:paddingLeft="@dimen/activity_horizontal_margin"
 android:paddingRight="@dimen/activity_horizontal_margin"
 android:orientation="vertical"
 android:paddingTop="@dimen/activity_vertical_margin"

 tools:context="com.example.bz0209.myapplication.MainActivity">
 <ImageView
 android:layout_weight="1000"
 android:id="@+id/iv"
 android:layout_width="fill_parent"
 android:layout_height="wrap_content"
 />
 <EditText
 android:singleLine="true"
 android:id="@+id/et_path"
 android:layout_width="fill_parent"
 android:layout_height="wrap_content"
 android:text="http://b.hiphotos.baidu.com/image/w%3D310/sign=a439f5b24510b912bfc1f0fff3fdfcb5/83025aafa40f4bfb92c52c5d014f78f0f73618a5.jpg"
 android:hint="请输入图片路径"
 />
 <Button
 android:onClick="click"
 android:layout_width="fill_parent"
 android:layout_height="wrap_content"
 android:text="浏览"
 />
</LinearLayout>

package com.example.bz0209.myapplication;

import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Handler;
import android.os.Message;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.text.TextUtils;
import android.view.View;
import android.widget.EditText;
import android.widget.ImageView;
import android.widget.Toast;

import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;

public class MainActivity extends AppCompatActivity {
 protected static final int CHANGE_UI=1;
 protected static final int ERROR=2;
 private EditText et_path;
 private ImageView iv;
 //主线创建消息处理器
 private Handler handler=new Handler(){
 public void handleMessage(android.os.Message msg){
  if (msg.what==CHANGE_UI){
  Bitmap bitmap=(Bitmap)msg.obj;
  iv.setImageBitmap(bitmap);
  }else if (msg.what==ERROR){
  Toast.makeText(MainActivity.this,"显示图片错误",0).show();
  }
 }

 };

 @Override
 protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.activity_main);
 et_path=(EditText)findViewById(R.id.et_path);
 iv=(ImageView) findViewById(R.id.iv);
 }
 public void click(View view){
 final String path=et_path.getText().toString().trim();
 if (TextUtils.isEmpty(path)){
  Toast.makeText(this,"图片路径不能为空",0).show();
 }

 else {
  //子线程请求网络，Android 4.0以后访问网络不能放在子线程中
  new Thread(){
  private HttpURLConnection conn;
  private Bitmap bitmap;
  public void run(){
   //链接服务器get请求，获取图片
   try{
   //创建URL对象
   URL url =new URL(path);
   conn=(HttpURLConnection) url.openConnection();
   conn.setRequestMethod("GET");
   conn.setConnectTimeout(5000);
   conn.setRequestProperty("User-Agent","Mozilla/4.0 (compatib;MSIE 6.0;Window NT 5.1;"+"SV1;" +
    ".NET4.0C;.NET4.0E;NET CLK 2.0.50727;"+".NET CLR 3.0..4506.2152;.NET CLR 3.5.30729; Shuame )");
   int code=conn.getResponseCode();
   if(code==200){
    InputStream is=conn.getInputStream();
    bitmap= BitmapFactory.decodeStream(is);
    Message msg=new Message();
    msg.what=CHANGE_UI;
    msg.obj=bitmap;
    handler.sendMessage(msg);
   }
   else {
    Message msg=new Message();
    msg.what=ERROR;
    handler.sendMessage(msg);

   }

   }catch (Exception e){
   e.printStackTrace();
   Message msg=new Message();
   msg.what=ERROR;

   }
  }
  }.start();
 }
 }
}