httpcomponents-client-4.5.3 学习笔记(1) 1.1 发送请求

1.1 发送请求

基本的发送请求例子如下：

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

新建一个HTTPGET请求：

HttpGet httpget = new HttpGet(     "http://www.google.com/search?hl=en&q=httpclient&btnG=Google+Search&aq=f&oq=");

其中的URI可以用URIBuider来构建：

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);System.out.println(httpget.getURI());

服务器响应信息的使用方法：

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());

打印效果：

HTTP/1.1200OKHTTP/1.1 200 OK

遍历响应头部的方法：

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\"");HeaderIterator it = response.headerIterator("Set-Cookie");while (it.hasNext()) {    System.out.println(it.next());}

打印效果：

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

这里还提供了遍历响应头部的另一种方法：

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\"");HeaderElementIterator it = new BasicHeaderElementIterator(    response.headerIterator("Set-Cookie"));while (it.hasNext()) {    HeaderElement elem = it.nextElement();     System.out.println(elem.getName() + " = " + elem.getValue());    NameValuePair[] params = elem.getParameters();    for (int i = 0; i < params.length; i++) {        System.out.println(" " + params[i]);    }}

PS:我认为原始的方法会更实用一点。

HTTP entity

HTTP entity 是保存能重复使用的请求或响应传递的信息。

以下是StringEntity的使用例子：

StringEntity myEntity = new StringEntity("important message",    ContentType.create("text/plain", "UTF-8"));System.out.println(myEntity.getContentType());System.out.println(myEntity.getContentLength());System.out.println(EntityUtils.toString(myEntity));System.out.println(EntityUtils.toByteArray(myEntity).length);

打印效果：

Content-Type: text/plain; charset=utf-817important message17

HttpEntity 的使用例子：

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();}

从HttpEntity获取网页信息：

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,"utf-8"));//utf-8可加可不加        } else {            // Stream content out        }    }} finally {    response.close();}

有时候HttpEntity要重复使用多次，你可以用BufferedHttpEntity把HttpEntity保存下来：

CloseableHttpResponse response = <...>HttpEntity entity = response.getEntity();if (entity != null) {    entity = new BufferedHttpEntity(entity);}

把文件发送post请求给服务器的方法：

File file = new File("somefile.txt");FileEntity entity = new FileEntity(file,     ContentType.create("text/plain", "UTF-8"));        HttpPost httppost = new HttpPost("http://localhost/action.do");httppost.setEntity(entity);

提交HTML表单的方法：

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);

你可以给服务器提供客户端推荐的传输编码，通过StringEntity的setChunked(true)的方法：

StringEntity entity = new StringEntity("important message",        ContentType.create("plain/text", Consts.UTF_8));entity.setChunked(true);HttpPost httppost = new HttpPost("http://localhost/acrtion.do");httppost.setEntity(entity);

你可以通过Response handlers来处理服务器的响应：

CloseableHttpClient httpclient = HttpClients.createDefault();HttpGet httpget = new HttpGet("http://localhost/json");ResponseHandler<MyJsonObject> rh = new ResponseHandler<MyJsonObject>() {    @Override    public JsonObject handleResponse(            final HttpResponse response) throws IOException {        StatusLine statusLine = response.getStatusLine();        HttpEntity entity = response.getEntity();        if (statusLine.getStatusCode() >= 300) {            throw new HttpResponseException(                    statusLine.getStatusCode(),                    statusLine.getReasonPhrase());        }        if (entity == null) {            throw new ClientProtocolException("Response contains no content");        }        Gson gson = new GsonBuilder().create();        ContentType contentType = ContentType.getOrDefault(entity);        Charset charset = contentType.getCharset();        Reader reader = new InputStreamReader(entity.getContent(), charset);        return gson.fromJson(reader, MyJsonObject.class);    }};MyJsonObject myjson = client.execute(httpget, rh);

这应该是一种设计思想，拿到服务器的响应想怎么处理就怎么处理，搞那么多干什么呢？然而你想把代码更具有通用性还是应该按这些设计思想去编写代码。