Android中使用HTTP服务 HttpClient API

在Android中,除了使用java.net包下的API访问HTTP服务之外,我们还可以换一种途径去完成工作。Android SDK附带了Apache的HttpClient API。Apache HttpClient是一个完善的HTTP客户端,它提供了对HTTP协议的全面支持,可以使用HTTP GET和POST进行访问。下面我们就结合实例,介绍一下HttpClient的使用方法。

我们新建一个http项目。

在这个项目中,我们不需要任何的Activity,所有的操作都在单元测试类HttpTest.java中完成。

因为使用到了单元测试,所以在这里先介绍一下如何配置Android中的单元测试。所有配置信息均在AndroidManifest.xml中完成:

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
      package="com.scott.http"
      android:versionCode="1"
      android:versionName="1.0">
    <application android:icon="@drawable/icon" android:label="@string/app_name">
        <!-- 配置测试要使用的类库 -->
        <uses-library android:name="android.test.runner"/>
    </application>
    <!-- 配置测试设备的主类和目标包 -->
    <instrumentation android:name="android.test.InstrumentationTestRunner"
					 android:targetPackage="com.scott.http"/>
	<!-- 访问HTTP服务所需的网络权限 -->
	<uses-permission android:name="android.permission.INTERNET"/>
	<uses-sdk android:minSdkVersion="8" />
</manifest> 

然后,我们的单元测试类需要继承android.test.AndroidTestCase类,这个类本身是继承junit.framework.TestCase,并提供了getContext()方法,用于获取Android上下文环境,这个设计非常有用,因为很多Android API都是需要Context才能完成的。

现在让我们来看一下我们的测试用例,HttpTest.java代码如下:

import java.io.ByteArrayOutputStream;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.List;

import junit.framework.Assert;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.HttpStatus;
import org.apache.http.NameValuePair;
import org.apache.http.client.HttpClient;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.entity.mime.MultipartEntity;
import org.apache.http.entity.mime.content.InputStreamBody;
import org.apache.http.entity.mime.content.StringBody;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.message.BasicNameValuePair;

import android.test.AndroidTestCase;

public class HttpTest extends AndroidTestCase {
	
	private static final String PATH = "http://192.168.1.57:8080/web";
	
	public void testGet() throws Exception {
		HttpClient client = new DefaultHttpClient();
    	HttpGet get = new HttpGet(PATH + "/TestServlet?id=1001&name=john&age=60");
    	HttpResponse response = client.execute(get);
    	if (response.getStatusLine().getStatusCode() == HttpStatus.SC_OK) {
        	InputStream is = response.getEntity().getContent();
        	String result = inStream2String(is);
        	Assert.assertEquals(result, "GET_SUCCESS");
    	}
	}
	
	public void testPost() throws Exception {
		HttpClient client = new DefaultHttpClient();
		HttpPost post = new HttpPost(PATH + "/TestServlet");
		List<NameValuePair> params = new ArrayList<NameValuePair>();
		params.add(new BasicNameValuePair("id", "1001"));
		params.add(new BasicNameValuePair("name", "john"));
		params.add(new BasicNameValuePair("age", "60"));
		HttpEntity formEntity = new UrlEncodedFormEntity(params);
		post.setEntity(formEntity);
		HttpResponse response = client.execute(post);
		if (response.getStatusLine().getStatusCode() == HttpStatus.SC_OK) {
        	InputStream is = response.getEntity().getContent();
        	String result = inStream2String(is);
        	Assert.assertEquals(result, "POST_SUCCESS");
    	}
	}
	
	public void testUpload() throws Exception {
		InputStream is = getContext().getAssets().open("books.xml");
		HttpClient client = new DefaultHttpClient();
		HttpPost post = new HttpPost(PATH + "/UploadServlet");
		InputStreamBody isb = new InputStreamBody(is, "books.xml");
		MultipartEntity multipartEntity = new MultipartEntity();
		multipartEntity.addPart("file", isb);
		multipartEntity.addPart("desc", new StringBody("this is description."));
		post.setEntity(multipartEntity);
		HttpResponse response = client.execute(post);
		if (response.getStatusLine().getStatusCode() == HttpStatus.SC_OK) {
        	is = response.getEntity().getContent();
        	String result = inStream2String(is);
        	Assert.assertEquals(result, "UPLOAD_SUCCESS");
    	}
	}
	
	//将输入流转换成字符串
	private String inStream2String(InputStream is) throws Exception {
		ByteArrayOutputStream baos = new ByteArrayOutputStream();
		byte[] buf = new byte[1024];
		int len = -1;
		while ((len = is.read(buf)) != -1) {
			baos.write(buf, 0, len);
		}
		return new String(baos.toByteArray());
	}
}

因为此文件包含三个测试用例,所以我将会逐个介绍一下。

首先,需要注意的是,我们定位服务器地址时使用到了IP,因为这里不能用localhost,服务端是在windows上运行,而本单元测试运行在Android平台,如果使用localhost就意味着在Android内部去访问服务,可能是访问不到的,所以必须用IP来定位服务。

我们先来分析一下testGet测试用例。我们使用了HttpGet,请求参数直接附在URL后面,然后由HttpClient执行GET请求,如果响应成功的话,取得响应内如输入流,并转换成字符串,最后判断是否为GET_SUCCESS。

testGet测试对应服务端Servlet代码如下:

@Override
	protected void doGet(HttpServletRequest request, HttpServletResponse response) 
		throws ServletException, IOException {
		System.out.println("doGet method is called.");
		String id = request.getParameter("id");
		String name = request.getParameter("name");
		String age = request.getParameter("age");
		System.out.println("id:" + id + ", name:" + name + ", age:" + age);
		response.getWriter().write("GET_SUCCESS");
	}

然后再说testPost测试用例。我们使用了HttpPost,URL后面并没有附带参数信息,参数信息被包装成一个由NameValuePair类型组成的集合的形式,然后经过UrlEncodedFormEntity处理后调用HttpPost的setEntity方法进行参数设置,最后由HttpClient执行。

testPost测试对应的服务端代码如下:

@Override
	protected void doPost(HttpServletRequest request, HttpServletResponse response) 
		throws ServletException, IOException {
		System.out.println("doPost method is called.");
		String id = request.getParameter("id");
		String name = request.getParameter("name");
		String age = request.getParameter("age");
		System.out.println("id:" + id + ", name:" + name + ", age:" + age);
		response.getWriter().write("POST_SUCCESS");
	}

上面两个是最基本的GET请求和POST请求,参数都是文本数据类型,能满足普通的需求,不过在有的场合例如我们要用到上传文件的时候,就不能使用基本的GET请求和POST请求了,我们要使用多部件的POST请求。下面介绍一下如何使用多部件POST操作上传一个文件到服务端。

由于Android附带的HttpClient版本暂不支持多部件POST请求,所以我们需要用到一个HttpMime开源项目,该组件是专门处理与MIME类型有关的操作。因为HttpMime是包含在HttpComponents 项目中的,所以我们需要去apache官方网站下载HttpComponents,然后把其中的HttpMime.jar包放到项目中去。

然后,我们观察testUpload测试用例,我们用HttpMime提供的InputStreamBody处理文件流参数,用StringBody处理普通文本参数,最后把所有类型参数都加入到一个MultipartEntity的实例中,并将这个multipartEntity设置为此次POST请求的参数实体,然后执行POST请求。服务端Servlet代码如下:

import java.io.FileOutputStream;
import java.io.IOException;
import java.util.Iterator;
import java.util.List;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.FileItemFactory;
import org.apache.commons.fileupload.FileUploadException;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;

@SuppressWarnings("serial")
public class UploadServlet extends HttpServlet {
	
	@Override
	@SuppressWarnings("rawtypes")
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		boolean isMultipart = ServletFileUpload.isMultipartContent(request);
		if (isMultipart) {
			FileItemFactory factory = new DiskFileItemFactory();
			ServletFileUpload upload = new ServletFileUpload(factory);
			try {
				List items = upload.parseRequest(request);
				Iterator iter = items.iterator();
				while (iter.hasNext()) {
				    FileItem item = (FileItem) iter.next();
				    if (item.isFormField()) {
				    	//普通文本信息处理
				    	String paramName = item.getFieldName();
				        String paramValue = item.getString();
				        System.out.println(paramName + ":" + paramValue);
				    } else {
				    	//上传文件信息处理
				        String fileName = item.getName();
				        byte[] data = item.get();
				        String filePath = getServletContext().getRealPath("/files") + "/" + fileName;
				        FileOutputStream fos = new FileOutputStream(filePath);
				        fos.write(data);
				        fos.close();
				    }
				}
			} catch (FileUploadException e) {
				e.printStackTrace();
			}
		}
		response.getWriter().write("UPLOAD_SUCCESS");
	}
}

服务端使用apache开源项目FileUpload进行处理,所以我们需要commons-fileupload和commons-io这两个项目的jar包,对服务端开发不太熟悉的朋友可以到网上查找一下相关资料。

介绍完上面的三种不同的情况之后,我们需要考虑一个问题,在实际应用中,我们不能每次都新建HttpClient,而是应该只为整个应用创建一个HttpClient,并将其用于所有HTTP通信。此外,还应该注意在通过一个HttpClient同时发出多个请求时可能发生的多线程问题。针对这两个问题,我们需要改进一下我们的项目:

1.扩展系统默认的Application,并应用在项目中。

2.使用HttpClient类库提供的ThreadSafeClientManager来创建和管理HttpClient。

其中MyApplication扩展了系统的Application,代码如下:

import org.apache.http.HttpVersion;
import org.apache.http.client.HttpClient;
import org.apache.http.conn.ClientConnectionManager;
import org.apache.http.conn.scheme.PlainSocketFactory;
import org.apache.http.conn.scheme.Scheme;
import org.apache.http.conn.scheme.SchemeRegistry;
import org.apache.http.conn.ssl.SSLSocketFactory;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.impl.conn.tsccm.ThreadSafeClientConnManager;
import org.apache.http.params.BasicHttpParams;
import org.apache.http.params.HttpParams;
import org.apache.http.params.HttpProtocolParams;
import org.apache.http.protocol.HTTP;

import android.app.Application;

public class MyApplication extends Application {

	private HttpClient httpClient;
	
	@Override
	public void onCreate() {
		super.onCreate();
		httpClient = this.createHttpClient();
	}
	
	@Override
	public void onLowMemory() {
		super.onLowMemory();
		this.shutdownHttpClient();
	}
	
	@Override
	public void onTerminate() {
		super.onTerminate();
		this.shutdownHttpClient();
	}
	
	//创建HttpClient实例
	private HttpClient createHttpClient() {
		HttpParams params = new BasicHttpParams();
		HttpProtocolParams.setVersion(params, HttpVersion.HTTP_1_1);
		HttpProtocolParams.setContentCharset(params, HTTP.DEFAULT_CONTENT_CHARSET);
		HttpProtocolParams.setUseExpectContinue(params, true);
		
		SchemeRegistry schReg = new SchemeRegistry();
		schReg.register(new Scheme("http", PlainSocketFactory.getSocketFactory(), 80));
		schReg.register(new Scheme("https", SSLSocketFactory.getSocketFactory(), 443));
		
		ClientConnectionManager connMgr = new ThreadSafeClientConnManager(params, schReg);
		
		return new DefaultHttpClient(connMgr, params);
	}
	
	//关闭连接管理器并释放资源
	private void shutdownHttpClient() {
		if (httpClient != null && httpClient.getConnectionManager() != null) {
			httpClient.getConnectionManager().shutdown();
		}
	}
	
	//对外提供HttpClient实例
	public HttpClient getHttpClient() {
		return httpClient;
	}
}

我们重写了onCreate()方法,在系统启动时就创建一个HttpClient;重写了onLowMemory()和onTerminate()方法,在内存不足和应用结束时关闭连接,释放资源。需要注意的是,当实例化DefaultHttpClient时,传入一个由ThreadSafeClientConnManager创建的一个ClientConnectionManager实例,负责管理HttpClient的HTTP连接。

然后,想要让我们这个加强版的“Application”生效,需要在AndroidManifest.xml中做如下配置:

<application  android:name=".MyApplication" ...>
...
</application>

如果我们没有配置,系统默认会使用android.app.Application,我们添加了配置,系统就会使用我们的com.scott.http.MyApplication,然后就可以在context中调用getApplication()来获取MyApplication实例。

有了上面的配置,我们就可以在活动中应用了,HttpActivity.java代码如下:

import java.io.ByteArrayOutputStream;
import java.io.InputStream;

import org.apache.http.HttpResponse;
import org.apache.http.HttpStatus;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;

public class HttpActivity extends Activity {
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.main);
		Button btn = (Button) findViewById(R.id.btn);
		btn.setOnClickListener(new View.OnClickListener() {
			@Override
			public void onClick(View v) {
				execute();
			}
		});
		
	}
	
	private void execute() {
		try {
			MyApplication app = (MyApplication) this.getApplication();	//获取MyApplication实例
			HttpClient client = app.getHttpClient();	//获取HttpClient实例
			HttpGet get = new HttpGet("http://192.168.1.57:8080/web/TestServlet?id=1001&name=john&age=60");
			HttpResponse response = client.execute(get);
			if (response.getStatusLine().getStatusCode() == HttpStatus.SC_OK) {
	        	InputStream is = response.getEntity().getContent();
	        	String result = inStream2String(is);
	        	Toast.makeText(this, result, Toast.LENGTH_LONG).show();
	    	}
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
	
	//将输入流转换成字符串
	private String inStream2String(InputStream is) throws Exception {
		ByteArrayOutputStream baos = new ByteArrayOutputStream();
		byte[] buf = new byte[1024];
		int len = -1;
		while ((len = is.read(buf)) != -1) {
			baos.write(buf, 0, len);
		}
		return new String(baos.toByteArray());
	}
}