Android Java – 如何从URL下载zip文件？
嘿我正在制作一个新项目，要求你从我的Dropbox下载一些文件。 我添加了一个名为DownloadFile的新类，它具有下载文件的代码。 出于某种原因，当我点击下载时，应用程序崩溃了。 谢谢。
inheritance下载文件：
package com.Matt7262.download.app; import android.support.v7.app.ActionBarActivity; import android.os.Bundle; import android.view.Menu; import android.view.MenuItem; //Chat bot library import org.alicebot.ab.Chat; import org.alicebot.ab.Bot; import android.view.View; import android.widget.Button; import android.os.Environment; import android.widget.TextView; import android.widget.Toast; import java.io.InputStream; import java.net.URL; import java.io.DataInputStream; import java.io.DataOutputStream; import java.io.File; import java.io.FileNotFoundException; import java.io.FileOutputStream; import java.io.IOException; import java.net.HttpURLConnection; import java.net.MalformedURLException; import android.widget.ProgressBar; import java.net.URL; import java.net.URLConnection; import android.app.Activity; import android.app.ProgressDialog; import android.os.Environment; import android.view.View.OnClickListener; public class DownloadFile extends ActionBarActivity{ public void updateProgress(int currentSize, int totalSize) { Toast.makeText(getApplicationContext(), "Loading Files...", Toast.LENGTH_SHORT).show(); } public void Download() { try { //set the download URL, a url that points to a file on the internet //this is the file to be downloaded URL url = new URL("https://dl.dropboxusercontent.com/shz/9cyfz0b45mj6szr/7pBuupNz3N/xecta?token_hash=AAEs9cDFswt98D1IhLnab4dHwhwh5z2Lmhq_N6H-2M0LWg&top_level_offset=6"); //create the new connection HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection(); //set up some things on the connection urlConnection.setRequestMethod("GET"); urlConnection.setDoOutput(true); //and connect! urlConnection.connect(); //set the path where we want to save the file //in this case, going to save it on the root directory of the //sd card. File SDCardRoot = Environment.getExternalStorageDirectory(); //create a new file, specifying the path, and the filename //which we want to save the file as. File file = new File(SDCardRoot,"hello.zip"); //this will be used to write the downloaded data into the file we created FileOutputStream fileOutput = new FileOutputStream(file); //this will be used in reading the data from the internet InputStream inputStream = urlConnection.getInputStream(); //this is the total size of the file int totalSize = urlConnection.getContentLength(); //variable to store total downloaded bytes int downloadedSize = 0; //create a buffer... byte[] buffer = new byte[1024]; int bufferLength = 0; //used to store a temporary size of the buffer //now, read through the input buffer and write the contents to the file while ( (bufferLength = inputStream.read(buffer)) > 0 ) { //add the data in the buffer to the file in the file output stream (the file on the sd card fileOutput.write(buffer, 0, bufferLength); //add up the size so we know how much is downloaded downloadedSize += bufferLength; //this is where you would do something to report the prgress, like this maybe updateProgress(downloadedSize, totalSize); } //close the output stream when done fileOutput.close(); //catch some possible errors... } catch (MalformedURLException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } } } 主要活动：
package com.Matt7262.download.app; import android.support.v7.app.ActionBarActivity; import android.os.Bundle; import android.view.Menu; import android.view.MenuItem; //Chat bot library import org.alicebot.ab.Chat; import org.alicebot.ab.Bot; import android.view.View; import android.widget.Button; import android.os.Environment; import android.widget.TextView; import android.widget.Toast; import android.os.AsyncTask; public class MainActivity extends ActionBarActivity { TextView input; String dPath = Environment.getExternalStorageDirectory().getAbsolutePath() + "/Download"; private DownloadFile df; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); } //EditText mEdit = (EditText)findViewById(R.id.editText1); public void buttonOnClick(View v) { input = (TextView) findViewById(R.id.editText1); String dbPath = Environment.getExternalStorageDirectory().getAbsolutePath() + "/Download/Ab"; Button button=(Button) v; //Creating bot String botname="xecta"; String path= dbPath; Bot xecta = new Bot(botname, path); Chat chatSession = new Chat(xecta); String request = input.getText().toString(); String response = chatSession.multisentenceRespond(request); ((Button) v).setText(response); } public void onClickDownload(View view) { df.Download(); } @Override public boolean onCreateOptionsMenu(Menu menu) { // Inflate the menu; this adds items to the action bar if it is present. getMenuInflater().inflate(R.menu.main, menu); return true; } @Override public boolean onOptionsItemSelected(MenuItem item) { // Handle action bar item clicks here. The action bar will // automatically handle clicks on the Home/Up button, so long // as you specify a parent activity in AndroidManifest.xml. int id = item.getItemId(); if (id == R.id.action_settings) { return true; } return super.onOptionsItemSelected(item); } /*public void updateProgress(int currentSize, int totalSize) { Toast.makeText(getApplicationContext(), "Retrieving Files...", Toast.LENGTH_SHORT).show(); }/* /*public void Download() { try { //set the download URL, a url that points to a file on the internet //this is the file to be downloaded URL url = new URL("https://dl.dropboxusercontent.com/shz/9cyfz0b45mj6szr/7pBuupNz3N/xecta?token_hash=AAEs9cDFswt98D1IhLnab4dHwhwh5z2Lmhq_N6H-2M0LWg&top_level_offset=6"); //create the new connection HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection(); //set up some things on the connection urlConnection.setRequestMethod("GET"); urlConnection.setDoOutput(true); //and connect! urlConnection.connect(); //set the path where we want to save the file //in this case, going to save it on the root directory of the //sd card. File SDCardRoot = Environment.getExternalStorageDirectory(); //create a new file, specifying the path, and the filename //which we want to save the file as. File file = new File(SDCardRoot,"hello.zip"); //this will be used to write the downloaded data into the file we created FileOutputStream fileOutput = new FileOutputStream(file); //this will be used in reading the data from the internet InputStream inputStream = urlConnection.getInputStream(); //this is the total size of the file int totalSize = urlConnection.getContentLength(); //variable to store total downloaded bytes int downloadedSize = 0; //create a buffer... byte[] buffer = new byte[1024]; int bufferLength = 0; //used to store a temporary size of the buffer //now, read through the input buffer and write the contents to the file while ( (bufferLength = inputStream.read(buffer)) > 0 ) { //add the data in the buffer to the file in the file output stream (the file on the sd card fileOutput.write(buffer, 0, bufferLength); //add up the size so we know how much is downloaded downloadedSize += bufferLength; //this is where you would do something to report the prgress, like this maybe updateProgress(downloadedSize, totalSize); } //close the output stream when done fileOutput.close(); //catch some possible errors... } catch (MalformedURLException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } }*/ }
我想这就是我从logcat中得到的：
logcat的
您正在声明DownloadFile对象但未初始化它。
private DownloadFile df; df.Download(); // Throws NPE
不要忘记初始化它。
private DownloadFile df = new DownloadFile(); df.Download();
编辑：
现在你初始化了对象并避免了NPE，但这次你得到的是NetworkOnMainThreadException 。 在Honeycomb版本之后，Android不允许您在主线程上进行网络操作。 您可以使用AsyncTask来克服这个问题。