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/1.1
200
OK
HTTP/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=localhost
Set-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-8
17
important message
17

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 formparams = new ArrayList();
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 rh = new ResponseHandler() {

    @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。