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Android中使用HTTP服务的用法详解

作者:liuhe688

这篇文章主要介绍了Android中使用HTTP服务的用法详解,有需要的可以了解一下。

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,项目结构如图:

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:

<?xml version="1.0" encoding="utf-8"?> 
<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:

package com.scot.http.test; 
 
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,如图:

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:

package com.scott.web.servlet; 
 
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。

改进后的项目结构如图:

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

package com.scott.http; 
 
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:

package com.scott.http; 
 
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()); 
  } 
} 

点击“execute”按钮,执行结果如下:

以上就是本文的全部内容,希望对大家的学习有所帮助,也希望大家多多支持脚本之家。

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