《HttpClient官方文檔》1.1 執行請求（一）

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

所有HTTP請求都有由方法名，請求URI和HTTP協議版本組成的請求行。

HttpClient支持開箱即用HTTP/1.1規範中定義的所有HTTP方法：GET, HEAD,POST, PUT, DELETE,TRACE and OPTIONS。它們都有一個特定的類對應這些方法類型: HttpGet,HttpHead, HttpPost,HttpPut, HttpDelete,HttpTrace, and HttpOptions.

請求的URI是統一資源定位符，它標識了應用於哪個請求之上的資源。HTTP請求的URI包含協議方案，主機名，可選的端口，資源路徑，可選查詢和可選片段。

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

HttpClient 提供 URIBuilder 實用類來簡化請求 URL的創建和修改.

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());

輸出內容為 >

https://www.google.com/search?q=httpclient&btnG=Google+Search&aq=f&oq=

HTTP響應是服務器端在接收和解釋客戶端請求消息後，返回客戶端的消息。該消息的第一行包含協議版本以及後麵跟著的數字形式的狀態代碼和相關的文本段。

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());

輸出內容為 >

HTTP/1.1
200
OK
HTTP/1.1 200 OK

HTTP消息可以包含多個描述該消息屬性的頭部諸如內容長度，內容類型等，HttpClient的提供方法來檢索，添加，刪除和枚舉這些頭部。

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);

輸出內容為 >

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

獲得所有頭部給定類型的最有效的方法是使用
HeaderIterator 接口.

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());
}

輸出內容為 >

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

它還提供了方便的方法來解析HTTP消息成為獨立頭部元素。

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]);
    }
}

輸出內容為 >

c1 = a
path=/
domain=localhost
c2 = b
path=/
c3 = c
domain=localhost