Java-HttpClient
HttpClient的介绍
一般步骤
- 取得HttpClient对象
- 封装http请求
- 执行http请求
- 处理结果
请求类型
GET, HEAD, POST, PUT, DELETE, TRACE 和 OPTIONS
官方示例
//1.获得一个httpclient对象
CloseableHttpClient httpclient = HttpClients.createDefault();
//2.生成一个get请求
HttpGet httpget = new HttpGet("http://localhost/");
//3.执行get请求并返回结果
CloseableHttpResponse response = httpclient.execute(httpget);
try {
//4.处理结果
} finally {
//5.关闭response
response.close();
}
HTTP request
拼接request
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);
发送HttpPost/HttpGet
举例：HttpGet请求，HttpPost类似
public static String sendGet(String url) {
//1.获得一个httpclient对象
CloseableHttpClient httpclient = HttpClients.createDefault();
//2.生成一个get请求
HttpGet httpget = new HttpGet(url);
CloseableHttpResponse response = null;
//3.执行get请求并返回结果
try {
response = httpclient.execute(httpget);
} catch (IOException e1) {
e1.printStackTrace();
}
String result = null;
//4.处理结果，这里将结果返回为字符串
try {
HttpEntity entity = response.getEntity();
if (entity != null) {
//内部使用完entity的流后，关闭流
result = EntityUtils.toString(entity);
}
} catch (ParseException | IOException e) {
e.printStackTrace();
} finally {
try {
//注意关闭response
response.close();
} catch (IOException e) {
e.printStackTrace();
}
}
return result;
}
带参数的HttpPost
HttpClient通过UrlEncodedFormEntity/StringEntity，来提交带参数的请求
UrlEncodedFormEntity：需要List<? extends NameValuePair>或者Iterable<? extends NameValuePair>
public interface NameValuePair {
String getName();
String getValue();
}
StringEntity：任意的字符串 (推荐使用)
public static String sendPost(String url, Map<String, String> map) {
//1.获得一个httpclient对象
CloseableHttpClient httpclient = HttpClients.createDefault();
List<NameValuePair> formparams = new ArrayList<NameValuePair>();
for (Map.Entry<String, String> entry : map.entrySet()) {
//给参数赋值
formparams.add(new BasicNameValuePair(entry.getKey(), entry.getValue()));
}
UrlEncodedFormEntity entity = new UrlEncodedFormEntity(formparams, Consts.UTF_8);
//2.生成一个post请求
HttpPost httppost = new HttpPost(url);
//3.放入参数
httppost.setEntity(entity);
//4.执行get请求并返回结果
CloseableHttpResponse response = null;
try {
response = httpclient.execute(httppost);
} catch (IOException e) {
e.printStackTrace();
}
//5.处理结果，这里将结果返回为字符串
String result = null;
try {
HttpEntity entity = response.getEntity();
if (entity != null) {
//内部使用完entity的流后，关闭流
result = EntityUtils.toString(entity);
}
} catch (ParseException | IOException e) {
e.printStackTrace();
}finally {
try {
//注意关闭response
response.close();
} catch (IOException e) {
e.printStackTrace();
}
}
return result;
}
用到的jar包有httpclient-4.5.1.jar，httpcore-4.4.3.jar，依赖的jar有commons-logging-1.2.jar
注意是Apache HttpClient，不是commons-httpclient
Response handlers
在处理结果时，我们不但要记得关闭response，还需要记得关闭response中entity的流。这种形式上的要求总是不安全的，一旦我们在编码中忘记了这两个步骤，就会导致连接没有被良好地复用等问题。所以在处理结果时，推荐使用ResponseHandler。
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);