Java4Android之httpclient学习与应用

在Java开发中,不可避免的需要和http打交道。而无论我司的迅雷动漫还是我主导的“搜芽”android客户端开发,都需要使用到http和服务器打交道。。虽然Java也提供了http的接口,但据我了解,更多的公司都是使用Apache的httpclient来进行开发,不仅因为它灵活强大,而且便捷。

今天,我们学习httpclient的基础知识。

关于Http的基础,在此就不再复习了。建议大家去看一本权威制作《HTTP权威指南》,加个略贵,109元人民币,不过,我买了,因为经典的书,还是多备一下,我也没怎么看,但遇到问题就翻即可。


闲话少说,切入正题。

我们发出一个http的请求,在httpclient中一般如下流程模式:

1. 创建HttpClient对象。
2. 创建请求方法的实例,并指定请求URL。如果需要发送GET请求,创建HttpGet对象;如果需要发送POST请求,创建HttpPost对象。
3. 如果需要发送请求参数,可调用HttpGet、HttpPost共同的setParams(HetpParams params)方法来添加请求参数;对于HttpPost对象而言,也可调用setEntity(HttpEntity entity)方法来设置请求参数
4. 调用HttpClient对象的execute(HttpUriRequest request)发送请求,该方法返回一个HttpResponse。
5. 调用HttpResponse的getAllHeaders()、getHeaders(String name)等方法可获取服务器的响应头;调用HttpResponse的getEntity()方法可获取HttpEntity对象,该对象包装了服务器的响应内容。程序可通过该对象获取服务器的响应内容。
6. 释放连接。无论执行方法是否成功,都必须释放连接.

代码示例如下:

CloseableHttpClient httpclient = HttpClients.createDefault();
HttpGet httpget = new HttpGet("http://localhost/");
CloseableHttpResponse response = httpclient.execute(httpget);
try {
<...>
} finally {
response.close();
}

请求:

HttpClient支持所有的HTTP/1.1的所有命令,包含:GET,HEAD,POST,PUT,DELETE,TRACE和OPTIONS。而且都有单独对应的类:HttpGet,HttpHead,....等等。

请求URI是统一资源标识符,标识了你所要请求的资源。它一般包含protocol scheme , host name, optional port, resource path,optional query ,optional fragment这些信息。如:

HttpGet httpget = new HttpGet(
"http://www.google.com/search?hl=en&q=httpclient&btnG=Google+Search&aq=f&oq=");
构造上述URI一个更为好的方法是使用URIBuilder。具体如下:

URI uri = new URIBuilder()
.setScheme("http")
.setHost("www.google.com")
.setPath("/search")
.setParameter("q", "httpclient")
.setParameter("btnG", "Google Search")
.setParameter("aq", "f")
.setParameter("oq", "")
.build();
HttpGet httpget = new HttpGet(uri);


回复:

回复(response)是服务器对客户端的回复。httpclient中的回复是HttpResponse.

HttpResponse response = new BasicHttpResponse(HttpVersion.HTTP_1_1,
HttpStatus.SC_OK, "OK");
System.out.println(response.getProtocolVersion());
System.out.println(response.getStatusLine().getStatusCode());
System.out.println(response.getStatusLine().getReasonPhrase());
System.out.println(response.getStatusLine().toString());
输出:
HTTP/1.1
200
OK
HTTP/1.1 200 OK

消息头部:

如果大家熟悉HTTP包的话,就知道一个HTTP报文是由三个部分组成的:对报文进行描述的起始行(start line),包含属性的首部块(header),以及可选的,包含数据的主体部分(body)。

httpclient的一个关于头部的示例:

HttpResponse response = new BasicHttpResponse(HttpVersion.HTTP_1_1,
HttpStatus.SC_OK, "OK");
response.addHeader("Set-Cookie",
"c1=a; path=/; domain=localhost");
response.addHeader("Set-Cookie",
"c2=b; path=\"/\", c3=c; domain=\"localhost\"");
Header h1 = response.getFirstHeader("Set-Cookie");
System.out.println(h1);
Header h2 = response.getLastHeader("Set-Cookie");
System.out.println(h2);
Header[] hs = response.getHeaders("Set-Cookie");
System.out.println(hs.length);

其输出结果:

Set-Cookie: c1=a; path=/; domain=localhost
Set-Cookie: c2=b; path="/", c3=c; domain="localhost"
2

HTTP 实体(entity):

在httpclient中存在三种实体,streamed,self-contained和wrapping。它们的区别在我们用到的时候再区分,一般而言,流对象适合接收流数据,self-contained自包含适合那些可重复读取的场景。wrapping是对已有实体的一个包装。
下面是一个使用实体的例子:
CloseableHttpClient httpclient = HttpClients.createDefault();
HttpGet httpget = new HttpGet("http://localhost/");
CloseableHttpResponse response = httpclient.execute(httpget);
try {
HttpEntity entity = response.getEntity();
if (entity != null) {
InputStream instream = entity.getContent();
try {
// do something useful
} finally {
instream.close();
}
}
} finally {
response.close();
}

对实体的使用:
CloseableHttpClient httpclient = HttpClients.createDefault();
HttpGet httpget = new HttpGet("http://localhost/");
CloseableHttpResponse response = httpclient.execute(httpget);
try {
HttpEntity entity = response.getEntity();
if (entity != null) {
long len = entity.getContentLength();
if (len != -1 && len < 2048) {
System.out.println(EntityUtils.toString(entity));
} else {
// Stream content out
}
}
} finally {
response.close();
}

那么,如何产生一个实体呢:
实体有分很多种类,所以httpclient也提供了几个产生实体的类,分别产生对应的实体。StringEntity,ByteArrayEntity,InputStreamEntity和FileEntity,它们分别产生string, byte array, input stream ,file。一个fileEntity的示例如下:
File file = new File("somefile.txt");
FileEntity entity = new FileEntity(file,
ContentType.create("text/plain", "UTF-8"));
HttpPost httppost = new HttpP

表单:
httpclient也提供了类似与http表单的功能,比如用户登入页面,需要用户名和密码。
List<NameValuePair> formparams = new ArrayList<NameValuePair>();
formparams.add(new BasicNameValuePair("param1", "value1"));
formparams.add(new BasicNameValuePair("param2", "value2"));
UrlEncodedFormEntity entity = new UrlEncodedFormEntity(formparams, Consts.UTF_8);
HttpPost httppost = new HttpPost("http://localhost/handler.do");
httppost.setEntity(entity);
会产生如下效果:
param1=value1&m2=value2


在最后,我给出我们对httpclient的GET和POST 的方法的一个封装,这里里面的代码会将我们前面讲到的元素都涉及到。
 private InputStream httpGet(String url, String cookie) {
        HttpGet httpGet = new HttpGet(url);
        httpGet.setHeader("Accept-Encoding", "gzip,deflate");
        if (!(TextUtils.isEmpty(cookie))) {
            httpGet.setHeader("Cookie", cookie);
        }
        return httpDo(httpGet, url, null);
    }

    private InputStream httpPost(String url, Map<String, String> headers,
            Map<String, Object> params) {
        HttpPost post = new HttpPost(url);

        HttpEntity entity = null;
        Object value = params.get(POST_ENTITY);
        if (value instanceof HttpEntity) {
            entity = (HttpEntity) value;
        } else {
            List<NameValuePair> pairs = new ArrayList<NameValuePair>();
            for (Map.Entry<String, Object> e : params.entrySet()) {
                value = e.getValue();
                if (value != null) {
                    LOG.debug("param=" + e.getKey() + ":" + value.toString());
                    pairs.add(new BasicNameValuePair(e.getKey(), value
                            .toString()));
                }
            }
            try {
                entity = new UrlEncodedFormEntity(pairs, "UTF-8");
            } catch (UnsupportedEncodingException e1) {
                LOG.warn("UnsupportedEncodingException err={}", e1.toString());
            }
        }

        if (headers != null && !headers.containsKey("Content-Type")) {
            headers.put("Content-Type",
                    "application/x-www-form-urlencoded;charset=UTF-8");
        }
        post.setEntity(entity);

        return httpDo(post, url, headers);
    }

    private InputStream httpDo(HttpUriRequest hr, String url,
            Map<String, String> headers) {
        InputStream in = null;
        if (headers != null) {
            for (String name : headers.keySet()) {
                hr.addHeader(name, headers.get(name));
            }
        }

        DefaultHttpClient client = getClient();
        HttpResponse response;
        try {
            response = client.execute(hr);

            int statusCode = response.getStatusLine().getStatusCode();
            LOG.debug("this={}, response code={}", this, statusCode);

            if (statusCode == HttpStatus.SC_OK) {
                HttpEntity entity = response.getEntity();
                if (null != entity) {
                    Header header = entity.getContentEncoding();
                    if (header != null && header.getValue().equals("gzip")) {
                        in = new GZIPInputStream(entity.getContent());
                    } else {
                        in = entity.getContent();
                    }
                }
            } else {
                LOG.warn("Request HTTP resource failed. StatusCode={} Url={}", statusCode, url);
            }
        } catch (IOException e) {
            LOG.warn("Request HTTP resource failed. {}, err={}", this, e.toString());
        } catch (IllegalStateException e) {
            LOG.warn("Request HTTP resource failed. url={} err={}", url, e.toString());
        }

        return in;
    }

    private static DefaultHttpClient getClient() {
        HttpParams httpParams = new BasicHttpParams();
        HttpConnectionParams.setConnectionTimeout(httpParams, CONNECTION_TIMEOUT);
        HttpConnectionParams.setSoTimeout(httpParams, SO_TIMEOUT);
        // http://stackoverflow.com/questions/5358014/android-httpclient-oom-on-4g-lte-htc-thunderbolt
        HttpConnectionParams.setSocketBufferSize(httpParams, 8192);

        return new DefaultHttpClient(httpParams);
    }

时间有限,今天到此为止。












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