原理
Android客户端模拟一个HTTP的Post请求到服务器端，服务器端接收相应的Post请求后，返回响应信息给给客户端。
PHP服务器
<?<span style="color: #000000;">php </span><span style="color: #008080;"> move_uploaded_file</span>(<span style="color: #800080;">$_FILES</span>['file']['tmp_name'], "./upload/".$_FILES["file"]["name"]); ?>
Android客户端
<span style="color: #0000ff;">package</span><span style="color: #000000;"> com.example.uploadfile.app;</span>
import android.app.Activity;
import android.os.Bundle;
import android.os.Environment;
import android.os.StrictMode;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;
import java.io.DataOutputStream;
import java.io.FileInputStream;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;
public class MainActivity extends Activity
{
private String fileName = “image.jpg”; //报文中的文件名参数
private String path = Environment.getExternalStorageDirectory().getPath(); //Don’t use “/sdcard/” here
private String uploadFile = path + “/” + fileName; //待上传的文件路径
private String postUrl = “http://mycloudnote.sinaapp.com/upload.php”; //处理POST请求的页面
private TextView mText1;
private TextView mText2;
private Button mButton;
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//“文件路径：\n”+
mText1 = (TextView) findViewById(R.id.myText1);
mText1.setText(uploadFile);
//“上传网址：\n”+
mText2 = (TextView) findViewById(R.id.myText2);
mText2.setText(postUrl);
/* 设置mButton的onClick事件处理 */
mButton = (Button) findViewById(R.id.myButton);
mButton.setOnClickListener(new View.OnClickListener()
{
public void onClick(View v)
{
uploadFile();
}
});
}
/* 上传文件至Server的方法 */
private void uploadFile()
{
String end = “\r\n”;
String twoHyphens = “–“;
String boundary = “*****”;
try
{
URL url = new URL(postUrl);
HttpURLConnection con = (HttpURLConnection) url.openConnection();
/* Output to the connection. Default is false,
set to true because post method must write something to the connection */
con.setDoOutput(true);
/* Read from the connection. Default is true.*/
con.setDoInput(true);
/* Post cannot use caches */
con.setUseCaches(false);
/* Set the post method. Default is GET*/
con.setRequestMethod(“POST”);
/* 设置请求属性 */
con.setRequestProperty(“Connection”, “Keep-Alive”);
con.setRequestProperty(“Charset”, “UTF-8”);
con.setRequestProperty(“Content-Type”, “multipart/form-data;boundary=” + boundary);
/*设置StrictMode 否则HTTPURLConnection连接失败，因为这是在主进程中进行网络连接*/
StrictMode.setThreadPolicy(new StrictMode.ThreadPolicy.Builder().detectDiskReads().detectDiskWrites().detectNetwork().penaltyLog().build());
/* 设置DataOutputStream，getOutputStream中默认调用connect()*/
DataOutputStream ds = new DataOutputStream(con.getOutputStream()); //output to the connection
ds.writeBytes(twoHyphens + boundary + end);
ds.writeBytes(“Content-Disposition: form-data; ” +
“name=\”file\”;filename=\”” +
fileName + “\”” + end);
ds.writeBytes(end);
/* 取得文件的FileInputStream */
FileInputStream fStream = new FileInputStream(uploadFile);
/* 设置每次写入8192bytes */
int bufferSize = 8192;
byte[] buffer = new byte[bufferSize]; //8k
int length = -1;
/* 从文件读取数据至缓冲区 */
while ((length = fStream.read(buffer)) != -1)
{
/* 将资料写入DataOutputStream中 */
ds.write(buffer, 0, length);
}
ds.writeBytes(end);
ds.writeBytes(twoHyphens + boundary + twoHyphens + end);
/* 关闭流，写入的东西自动生成Http正文*/
fStream.close();
/* 关闭DataOutputStream */
ds.close();
/* 从返回的输入流读取响应信息 */
InputStream is = con.getInputStream(); //input from the connection 正式建立HTTP连接
int ch;
StringBuffer b = new StringBuffer();
while ((ch = is.read()) != -1)
{
b.append((char) ch);
}
/* 显示网页响应内容 */
Toast.makeText(MainActivity.this, b.toString().trim(), Toast.LENGTH_SHORT).show();//Post成功
} catch (Exception e)
{
/* 显示异常信息 */
Toast.makeText(MainActivity.this, “Fail:” + e, Toast.LENGTH_SHORT).show();//Post失败
}
}
}
设置连接（HTTP头） -> 建立TCP连接 -> 设置HTTP正文 -> 建立HTTP连接（正式Post）-> 从返回的输入流读取响应信息
1.设置连接（HTTP头）
URL url = <span style="color: #0000ff;">new</span><span style="color: #000000;"> URL(postUrl);</span>
HttpURLConnection con = (HttpURLConnection) url.openConnection();
/* Output to the connection. Default is false,
set to true because post method must write something to the connection */
con.setDoOutput(true);
/* Read from the connection. Default is true.*/
con.setDoInput(true);
/* Post cannot use caches */
con.setUseCaches(false);
/* Set the post method. Default is GET*/
con.setRequestMethod(“POST”);
/* 设置请求属性 */
con.setRequestProperty(“Connection”, “Keep-Alive”);
con.setRequestProperty(“Charset”, “UTF-8”);
con.setRequestProperty(“Content-Type”, “multipart/form-data;boundary=” + boundary);
2.建立TCP连接
DataOutputStream ds = <span style="color: #0000ff;">new</span> DataOutputStream(con.getOutputStream()); <span style="color: #008000;">//</span><span style="color: #008000;">output to the connection</span>
con.getOutputStream()中会默认调用con.connect()，此时客户端与服务器建立的只是1个TCP连接而非HTTP。
HTTP请求=HTTP头+HTTP正文。
在connect()里面，会根据HttpURLConnection对象的配置值生成HTTP头，所以对con的一切配置都必须在connect()方法之前完成。
3.设置HTTP正文
正文通过DataOutputStream写入，只是写入内存而不会发送到网络中去，而是在流关闭时，根据写入的内容生成HTTP正文。
ds.writeBytes(twoHyphens + boundary +<span style="color: #000000;"> end);</span>
ds.writeBytes(“Content-Disposition: form-data; ” +
“name=\”file\”;filename=\”” +
fileName + “\”” + end);
ds.writeBytes(end);
/* 取得文件的FileInputStream */
FileInputStream fStream = new FileInputStream(uploadFile);
/* 设置每次写入8192bytes */
int bufferSize = 8192;
byte[] buffer = new byte[bufferSize]; //8k
int length = -1;
/* 从文件读取数据至缓冲区 */
while ((length = fStream.read(buffer)) != -1)
{
/* 将资料写入DataOutputStream中 */
ds.write(buffer, 0, length);
}
ds.writeBytes(end);
ds.writeBytes(twoHyphens + boundary + twoHyphens + end);
/* 关闭流，写入的东西自动生成Http正文*/
fStream.close();
/* 关闭DataOutputStream */
ds.close();
4.建立HTTP连接（正式Post）
至此，HTTP请求设置完毕，con.getInputStream()中会将请求（HTTP头+HTTP正文）发送到服务器，并返回一个输入流。所以在getInputStream()之前，HTTP正文部分一定要先设置好。
InputStream is = con.getInputStream(); <span style="color: #008000;">//</span><span style="color: #008000;">input from the connection 正式建立HTTP连接</span>
5.从返回的输入流读取响应信息
<span style="color: #0000ff;">int</span><span style="color: #000000;"> ch;</span>
StringBuffer b = new StringBuffer();
while ((ch = is.read()) != -1)
{
b.append((char) ch);
}
/* 显示网页响应内容 */
Toast.makeText(MainActivity.this, b.toString().trim(), Toast.LENGTH_SHORT).show();//Post成功
布局XML
两个Text和一个Button
<span style="color: #0000ff;"><</span><span style="color: #800000;">RelativeLayout </span><span style="color: #ff0000;">xmlns:android</span><span style="color: #0000ff;">="http://schemas.android.com/apk/res/android"</span>
xmlns:tools=”http://schemas.android.com/tools”
android:layout_width=”match_parent”
android:layout_height=”match_parent”
tools:context=”${packageName}.${activityClass}”>
<TextView
android:layout_width=”wrap_content”
android:layout_height=”wrap_content”
android:text=”New Text”
android:id=”@+id/myText1″
android:layout_above=”@+id/myText2″
android:layout_centerHorizontal=”true”
android:layout_marginBottom=”80dp”/>
<TextView
android:layout_width=”wrap_content”
android:layout_height=”wrap_content”
android:text=”New Text”
android:id=”@+id/myText2″
android:layout_centerVertical=”true”
android:layout_centerHorizontal=”true”/>
<Button
android:layout_width=”wrap_content”
android:layout_height=”wrap_content”
android:text=”Upload”
android:id=”@+id/myButton”
android:layout_marginTop=”80dp”
android:layout_below=”@+id/myText2″
android:layout_centerHorizontal=”true”/>
</RelativeLayout>
AndroidManifest
添加网络权限、SD卡读写权限、挂载文件系统权限。
<span style="color: #0000ff;"><?</span><span style="color: #ff00ff;">xml version="1.0" encoding="utf-8"</span><span style="color: #0000ff;">?></span>
<manifest xmlns:android=”http://schemas.android.com/apk/res/android”
package=”com.example.uploadfile.app” >
<application
android:allowBackup=”true”
android:icon=”@drawable/ic_launcher”
android:label=”@string/app_name”
android:theme=”@style/AppTheme” >
<activity
android:name=”com.example.uploadfile.app.MainActivity”
android:label=”@string/app_name” >
<intent-filter>
<action android:name=”android.intent.action.MAIN” />
<category android:name=”android.intent.category.LAUNCHER” />
</intent-filter>
</activity>
</application>
<uses-sdk android:minSdkVersion=”9″ android:targetSdkVersion=”15″ />
<uses-permission android:name=”android.permission.INTERNET” />
<uses-permission android:name=”android.permission.WRITE_EXTERNAL_STORAGE”/>
<uses-permission android:name=”android.permission.MOUNT_UNMOUNT_FILESYSTEMS”/>
</manifest>
注意事项
1.由于Android不建议在主进程中进行网络访问，所以使用HttpURLConnection连接到服务端时抛出异常，加入以下语句即可。
StrictMode.setThreadPolicy(<span style="color: #0000ff;">new</span> StrictMode.ThreadPolicy.Builder().detectDiskReads().detectDiskWrites().detectNetwork().penaltyLog().build());
2.获取SD卡路径时，请使用Environment.getExternalStorageDirectory().getPath();而不是”/sdcard/”
参考文章
HttpURLConnection学习
Android上传文件到Web服务器，PHP接收文件（一）
【Android开发那点破事】解决Andriod使用HttpURLConnection 失败问题