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Recently made an android software, you need to download files from the server. I am referring to mars video file to download, do first a little experiment. Do not know why urlConn.getInputStream () has been throwing NullPointerException. Here are some of the code used (last have all the code of the article):
url = new URL (urlStr);
HttpURLConnection urlConn = (HttpURLConnection) url.openConnection ();
buffer = new BufferedReader (new InputStreamReader (urlConn.getInputStream ())); / / Proven is urlConn.getInputStream () throw Exception
1, I have added AndroidManifest.xml file permissions
<-! Required permission to use network functions ->
2, I'm on my phone's browser to access tomcat under urlStr specified file, so it should be no problem
urlStr
Here are all the codes:
Download.java
package com.example.download;
import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import com.example.utils.HttpDownloader;
public class Download extends Activity {
Button downloadTextButton;
Button downloadMP3Button;
@ Override
protected void onCreate (Bundle savedInstanceState) {
super.onCreate (savedInstanceState);
setContentView (R.layout.activity_download);
downloadTextButton = (Button) findViewById (R.id.button1);
downloadTextButton.setOnClickListener (new OnClickListener () {
@ Override
public void onClick (View v) {
/ / TODO Auto-generated method stub5
HttpDownloader httpDownloader = new HttpDownloader ();
String text = httpDownloader.download ("http://192.l68.0.106:8080/test/a1.txt");
System.out.println (text);
}
});
downloadMP3Button = (Button) findViewById (R.id.button2);
downloadMP3Button.setOnClickListener (new OnClickListener () {
@ Override
public void onClick (View v) {
/ / TODO Auto-generated method stub
HttpDownloader httpDownloader = new HttpDownloader ();
int result = httpDownloader.downFile ("http://192.168.0.106:8080/test/a1.mp3", "test /", "a1.mp3");
System.out.println (result);
}
});
}
@ Override
public boolean onCreateOptionsMenu (Menu menu) {
/ / Inflate the menu; this adds items to the action bar if it is present
.getMenuInflater () inflate (R.menu.download, menu);.
return true;
}
}
HttpDownloader.java
package com.example.utils;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
public class HttpDownloader {
private URL url = null;
/ **
* According to the URL to download the file, provided that the contents of this document which is a text, the function's return value is the contents of the text which
* 1. Create a URL object
* 2 via a URL object, create an object
HttpURLConnection* 3. Obtain InputStream
* 4. Reading data from InputStream which
* @ Param urlStr
* @ Return
* /
public String download (String urlStr) {
StringBuffer sb = new StringBuffer ();
String line = null;
BufferedReader buffer = null;
try {
url = new URL (urlStr);
HttpURLConnection urlConn = (HttpURLConnection) url.openConnection ();
buffer = new BufferedReader (new InputStreamReader (urlConn.getInputStream ()));
while ((line = buffer.readLine ())! = null) {
sb.append (line);
}
} Catch (Exception e) {
e.printStackTrace ();
} Finally {
try {
buffer.close ();
} Catch (IOException e) {
e.printStackTrace ();
}
}
return sb.toString ();
}
/ **
*
* @ Param urlStr
* @ Param path
* @ Param fileName
* @ Return
* -1: File download error
* 0: File successfully downloaded
* 1: The file already exists
* /
public int downFile (String urlStr, String path, String fileName) {
InputStream inputStream = null;
try {
FileUtils fileUtils = new FileUtils ();
if (fileUtils.isFileExist (path + fileName)) {
return 1;
} Else {
inputStream = getInputStreamFromURL (urlStr);
File resultFile = fileUtils.write2SDFromInput (path, fileName, inputStream);
if (resultFile == null) {
return -1;
}
}
}
catch (Exception e) {
e.printStackTrace ();
return -1;
}
finally {
try {
inputStream.close ();
} Catch (IOException e) {
e.printStackTrace ();
}
}
return 0;
}
/ **
* According to the URL to get the input stream
* @ Param urlStr
* @ Return
* /
public InputStream getInputStreamFromURL (String urlStr) {
HttpURLConnection urlConn = null;
InputStream inputStream = null;
try {
url = new URL (urlStr);
urlConn = (HttpURLConnection) url.openConnection ();
inputStream = urlConn.getInputStream ();
} Catch (MalformedURLException e) {
e.printStackTrace ();
} Catch (IOException e) {
e.printStackTrace ();
}
return inputStream;
}
}
FileUtils.java
package com.example.utils;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
public class HttpDownloader {
private URL url = null;
/ **
* According to the URL to download the file, provided that the contents of this document which is a text, the function's return value is the contents of the text which
* 1. Create a URL object
* 2 via a URL object, create an object
HttpURLConnection* 3. Obtain InputStream
* 4. Reading data from InputStream which
* @ Param urlStr
* @ Return
* /
public String download (String urlStr) {
StringBuffer sb = new StringBuffer ();
String line = null;
BufferedReader buffer = null;
try {
url = new URL (urlStr);
HttpURLConnection urlConn = (HttpURLConnection) url.openConnection ();
buffer = new BufferedReader (new InputStreamReader (urlConn.getInputStream ()));
while ((line = buffer.readLine ())! = null) {
sb.append (line);
}
} Catch (Exception e) {
e.printStackTrace ();
} Finally {
try {
buffer.close ();
} Catch (IOException e) {
e.printStackTrace ();
}
}
return sb.toString ();
}
/ **
*
* @ Param urlStr
* @ Param path
* @ Param fileName
* @ Return
* -1: File download error
* 0: File successfully downloaded
* 1: The file already exists
* /
public int downFile (String urlStr, String path, String fileName) {
InputStream inputStream = null;
try {
FileUtils fileUtils = new FileUtils ();
if (fileUtils.isFileExist (path + fileName)) {
return 1;
} Else {
inputStream = getInputStreamFromURL (urlStr);
File resultFile = fileUtils.write2SDFromInput (path, fileName, inputStream);
if (resultFile == null) {
return -1;
}
}
}
catch (Exception e) {
e.printStackTrace ();
return -1;
}
finally {
try {
inputStream.close ();
} Catch (IOException e) {
e.printStackTrace ();
}
}
return 0;
}
/ **
* According to the URL to get the input stream
* @ Param urlStr
* @ Return
* /
public InputStream getInputStreamFromURL (String urlStr) {
HttpURLConnection urlConn = null;
InputStream inputStream = null;
try {
url = new URL (urlStr);
urlConn = (HttpURLConnection) url.openConnection ();
inputStream = urlConn.getInputStream ();
} Catch (MalformedURLException e) {
e.printStackTrace ();
} Catch (IOException e) {
e.printStackTrace ();
}
return inputStream;
}
}
activity_download.xml
xmlns: tools = "http://schemas.android.com/tools"
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: paddingTop = "@ dimen / activity_vertical_margin"
tools: context = "Download.">
android: id = "@ + id/button1"
android: layout_width = "match_parent"
android: layout_height = "wrap_content"
android: layout_alignParentLeft = "true"
android: layout_alignParentRight = "true"
android: layout_alignParentTop = "true"
android: text = "text file to download" />
android: id = "@ + id/button2"
android: layout_width = "match_parent"
android: layout_height = "wrap_content"
android: layout_alignLeft = "@ + id/button1"
android: layout_below = "@ + id/button1"
android: text = "Download MP3 file" />
AndroidManifest.xml
package = "com.example.download"
android: versionCode = "1"
android: versionName = "1.0">android: minSdkVersion = "8"
android: targetSdkVersion = "14" />android: allowBackup = "true"
android: icon = "@ drawable / ic_launcher"
android: label = "@ string / app_name"
android: theme = "@ style / AppTheme">android: name = "com.example.download.Download"
android: label = "@ string / app_name">
<-! Required permission to use network functions ->
<-! Main posts under Banner (D4) -><-! Posts under the main text (D5) ->
Reply:
http request to put the child thread.
Reply:
I see the video is not the child thread, you can achieve download
Reply:
4.0 to be used in sub-thread access network
Reply:
Thank you, finally AsyncTask achieved. Reference http://www.cnblogs.com/xiaoluo501395377/p/3430542.html
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