HttpClient ---------- 服務器請求外部service

HttpClient是Apache Jakarta Common下的子項目，可以用來提供高校的、最新的、功能豐富的支持HTTP協議的客戶端編程工具包，並支持HTTP協議最新的版本和建議。
基於httpClient4.5總結，不同版本有一些變化

功能

1. 實現了所有HTTP的方法（GET, POST, PUT, HEAD等）
2. 支持自動轉向
3. 支持HTTPS協議
4. 支持代理服務器等

實現步驟

1. 創建HttpClient實例
   “`java
   HttpClient client = HttpClients.createDefault();

2. 創建某種連接方法的實例Method(GET,POST等)
```java
HttpPost post = new HttpPost(url);
HttpGet get = new HttpGet(url);




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1. 參數設置
   兩種方式設置參數的方法：

   • Request-line
     在請求行上通過URI直接提供參數

   直接拼接在URI後面
   pl url? paramA=a¶mB=b
   URIUtils工具類
   pl.
   “`java
   URI uri = URIUtils.createURI(scheme, host, port, path, query, fragment);
   URI uri = URIUtils.createURI(“http”, “localhost”, 80, “/login.html”, “paramA=A¶mB=B”, null);
   URLEncoder.encode(“中國”, “UTF-8”) 解決中文亂碼問題

    URLEncodedUtils工具類
    pl.
    ```java
List <NameValuePair> list = new ArrayList<NameValuePair>();
list.add(new BasicNameValuePair("params", "A"));
list.add(new BasicNameValuePair("paramB", "B"));
String param = URLEncodedUtils.format(list, "UTF-8");
//調用URIUtils方法




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• request-body
  將參數放到request-body中。僅用於POST請求
  (1) UrlEncodedFormEntity類
  pl.
  “`java
  List list = new ArrayList();
  list.add(new BasicNameValuePair(“params”, “A”));
  list.add(new BasicNameValuePair(“paramB”, “B”));
  HttpEntity entity = new UrlEncodedFormEntity(list);
  HttpPost post = new HttpPost(url);
  post.setEntity(entity);

    (2) MultipartEntity類
    pl.
    ```java
HttpPost post = new HttpPost(url);
MultipartEntity entity = new MultipartEntity();
ntity.addPart("ParamA", new StringBody("中國", Charset.forName("UTF-8")));
entity.addPart("paramb", new FileBody(new File("c.txt")));
post.setEntity(entity);




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詳解： http://http://blog.csdn.net/chenyi_home/article/details/17240457
(3) MultipartEntityBuilder
pl.

MultipartEntityBuilder  builder = MultipartEntityBuilder.create();
builder.addBinaryBody(name, stream, ContentType.MULTIPART_FORM_DATA, filename);
builder.addTextBody(name, text);
builder.addPart(name, contentBody);
HttpEntity entity = (HttpEntity) builder.create();




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1. HttpClient來執行Method
   pl.

HttpResponse res =  client.execute(post);




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狀態判斷：

StatusLine statusLine =  res.getStatusLine();
int statusCode = statusLine.getStatusCode();
statusCode == HttpStatus.SC_OK




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HttpStatus 擁有請求的不同的狀態:
404 HttpStatus.SC_NOT_ACCEPTABLE
500 HttpStatus.SC_INTERNAL_SERVER_ERROR
200 HttpStatus.SC_OK
請求轉發的狀態碼：
301 HttpStatus.SC_MOVED_TEMPORARILY
302 HttpStatus.SC_MOVED_PERMANENTLY
303 HttpStatus.SC_SEE_OTHER
307 HttpStatus.SC_TEMPORARY_REDIRECT
轉發代碼（自動轉向）：

if (statusCode == HttpStatus.SC_SEE_OTHER) {
    Header[] Headers = res.getHeaders("location");
    for (Header header: Headers) {
        String newUrl = header.getValue();
        //重新請求
    }
}




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Http協議狀態碼：http://www.cnblogs.com/shanyou/archive/2012/05/06/2486134.html

1. 讀取response
   pl.

HttpEntity entity =  res.getEntity();
InputStream in = entity.getContent();
String content = entity.toString();

6 釋放鏈接，處理業務
最新幾個版本不需要自己釋放鏈接
得到in, content處理業務

HttpEntity

BasicHttpEntity  底層流的基本實體， 通常爲在http報文中獲取的實體
ByteArrayEntity  從指定字節數組中取出內容實體
StringEntity   通過String創建的實體
InputStreamEntity
FileEntity
EntityTemplete    從ContentProducer獲取內容的實體
HttpEntityWrapper  實體類的代理類
BufferedHttpEntity HttpEntityWrapper的子類

詳情：http://blog.csdn.net/haluoluo211/article/details/52085880