Httpclient是我们平时中用的比较多的，但是一般用的时候都是去网上百度一下，把demo直接拿过来改一下用就行了，接下来我们来看他的一些具体的用法。Apache HttpComponents™项目负责创建和维护一个专注于HTTP和相关协议的低级Java组件工具集。该项目在Apache软件基金会下运行，并且是更大的开发人员和用户社区的一部分。
很多情况下我们都会用到HttpClient来发送Get请求，下面我来看下具体的代码：
CloseableHttpClient httpclient = HttpClients.createDefalt();
HttpGet httpget = new HttpGet("http://www.baidu.com");
RequestConfig requestConfig = RequestConfig.custom().setConnectTimeout(50000).setSocketTimeout(50000)
.setConnectionRequestTimeout(3000).build();
httpget.setConfig(requestConfig);
CloseableHttpResponse response = httpClient.execute(httpget);
if (response != null) {
HttpEntity entity = response.getEntity(); // 获取返回实体
if (entity != null) {
EntityUtils.toString(entity)
}
}这是CloseableHttpClient的源码可知：
这个类继承自HttpClient，我们继续分析HttpClient类，可以看到他是顶级的接口类。
HttpClients的一些工具类，我们来看：
继续看build是个什么东西：
public CloseableHttpClient build() {
// Create main request executor
// We copy the instance fields to avoid changing them, and rename to avoid accidental use of the wrong version
PublicSuffixMatcher publicSuffixMatcherCopy = this.publicSuffixMatcher;
if (publicSuffixMatcherCopy == null) {
publicSuffixMatcherCopy = PublicSuffixMatcherLoader.getDefault();
}
HttpRequestExecutor requestExecCopy = this.requestExec;
if (requestExecCopy == null) {
requestExecCopy = new HttpRequestExecutor();
}
HttpClientConnectionManager connManagerCopy = this.connManager;
if (connManagerCopy == null) {
LayeredConnectionSocketFactory sslSocketFactoryCopy = this.sslSocketFactory;
if (sslSocketFactoryCopy == null) {
final String[] supportedProtocols = systemProperties ? split(
System.getProperty("https.protocols")) : null;
final String[] supportedCipherSuites = systemProperties ? split(
System.getProperty("https.cipherSuites")) : null;
HostnameVerifier hostnameVerifierCopy = this.hostnameVerifier;
if (hostnameVerifierCopy == null) {
hostnameVerifierCopy = new DefaultHostnameVerifier(publicSuffixMatcherCopy);
}
if (sslContext != null) {
sslSocketFactoryCopy = new SSLConnectionSocketFactory(
sslContext, supportedProtocols, supportedCipherSuites, hostnameVerifierCopy);
} else {
if (systemProperties) {
sslSocketFactoryCopy = new SSLConnectionSocketFactory(
(SSLSocketFactory) SSLSocketFactory.getDefault(),
supportedProtocols, supportedCipherSuites, hostnameVerifierCopy);
} else {
sslSocketFactoryCopy = new SSLConnectionSocketFactory(
SSLContexts.createDefault(),
hostnameVerifierCopy);
}
}
}
@SuppressWarnings("resource")
final PoolingHttpClientConnectionManager poolingmgr = new PoolingHttpClientConnectionManager(
RegistryBuilder.<ConnectionSocketFactory>create()
.register("http", PlainConnectionSocketFactory.getSocketFactory())
.register("https", sslSocketFactoryCopy)
.build(),
null,
null,
dnsResolver,
connTimeToLive,
connTimeToLiveTimeUnit != null ? connTimeToLiveTimeUnit : TimeUnit.MILLISECONDS);
if (defaultSocketConfig != null) {
poolingmgr.setDefaultSocketConfig(defaultSocketConfig);
}
if (defaultConnectionConfig != null) {
poolingmgr.setDefaultConnectionConfig(defaultConnectionConfig);
}
if (systemProperties) {
String s = System.getProperty("http.keepAlive", "true");
if ("true".equalsIgnoreCase(s)) {
s = System.getProperty("http.maxConnections", "5");
final int max = Integer.parseInt(s);
poolingmgr.setDefaultMaxPerRoute(max);
poolingmgr.setMaxTotal(2 * max);
}
}
if (maxConnTotal > 0) {
poolingmgr.setMaxTotal(maxConnTotal);
}
if (maxConnPerRoute > 0) {
poolingmgr.setDefaultMaxPerRoute(maxConnPerRoute);
}
connManagerCopy = poolingmgr;
}
ConnectionReuseStrategy reuseStrategyCopy = this.reuseStrategy;
if (reuseStrategyCopy == null) {
if (systemProperties) {
final String s = System.getProperty("http.keepAlive", "true");
if ("true".equalsIgnoreCase(s)) {
reuseStrategyCopy = DefaultClientConnectionReuseStrategy.INSTANCE;
} else {
reuseStrategyCopy = NoConnectionReuseStrategy.INSTANCE;
}
} else {
reuseStrategyCopy = DefaultClientConnectionReuseStrategy.INSTANCE;
}
}
ConnectionKeepAliveStrategy keepAliveStrategyCopy = this.keepAliveStrategy;
if (keepAliveStrategyCopy == null) {
keepAliveStrategyCopy = DefaultConnectionKeepAliveStrategy.INSTANCE;
}
AuthenticationStrategy targetAuthStrategyCopy = this.targetAuthStrategy;
if (targetAuthStrategyCopy == null) {
targetAuthStrategyCopy = TargetAuthenticationStrategy.INSTANCE;
}
AuthenticationStrategy proxyAuthStrategyCopy = this.proxyAuthStrategy;
if (proxyAuthStrategyCopy == null) {
proxyAuthStrategyCopy = ProxyAuthenticationStrategy.INSTANCE;
}
UserTokenHandler userTokenHandlerCopy = this.userTokenHandler;
if (userTokenHandlerCopy == null) {
if (!connectionStateDisabled) {
userTokenHandlerCopy = DefaultUserTokenHandler.INSTANCE;
} else {
userTokenHandlerCopy = NoopUserTokenHandler.INSTANCE;
}
}
String userAgentCopy = this.userAgent;
if (userAgentCopy == null) {
if (systemProperties) {
userAgentCopy = System.getProperty("http.agent");
}
if (userAgentCopy == null) {
userAgentCopy = VersionInfo.getUserAgent("Apache-HttpClient",
"org.apache.http.client", getClass());
}
}
ClientExecChain execChain = createMainExec(
requestExecCopy,
connManagerCopy,
reuseStrategyCopy,
keepAliveStrategyCopy,
new ImmutableHttpProcessor(new RequestTargetHost(), new RequestUserAgent(userAgentCopy)),
targetAuthStrategyCopy,
proxyAuthStrategyCopy,
userTokenHandlerCopy);
execChain = decorateMainExec(execChain);
HttpProcessor httpprocessorCopy = this.httpprocessor;
if (httpprocessorCopy == null) {
final HttpProcessorBuilder b = HttpProcessorBuilder.create();
if (requestFirst != null) {
for (final HttpRequestInterceptor i: requestFirst) {
b.addFirst(i);
}
}
if (responseFirst != null) {
for (final HttpResponseInterceptor i: responseFirst) {
b.addFirst(i);
}
}
b.addAll(
new RequestDefaultHeaders(defaultHeaders),
new RequestContent(),
new RequestTargetHost(),
new RequestClientConnControl(),
new RequestUserAgent(userAgentCopy),
new RequestExpectContinue());
if (!cookieManagementDisabled) {
b.add(new RequestAddCookies());
}
if (!contentCompressionDisabled) {
if (contentDecoderMap != null) {
final List<String> encodings = new ArrayList<String>(contentDecoderMap.keySet());
Collections.sort(encodings);
b.add(new RequestAcceptEncoding(encodings));
} else {
b.add(new RequestAcceptEncoding());
}
}
if (!authCachingDisabled) {
b.add(new RequestAuthCache());
}
if (!cookieManagementDisabled) {
b.add(new ResponseProcessCookies());
}
if (!contentCompressionDisabled) {
if (contentDecoderMap != null) {
final RegistryBuilder<InputStreamFactory> b2 = RegistryBuilder.create();
for (final Map.Entry<String, InputStreamFactory> entry: contentDecoderMap.entrySet()) {
b2.register(entry.getKey(), entry.getValue());
}
b.add(new ResponseContentEncoding(b2.build()));
} else {
b.add(new ResponseContentEncoding());
}
}
if (requestLast != null) {
for (final HttpRequestInterceptor i: requestLast) {
b.addLast(i);
}
}
if (responseLast != null) {
for (final HttpResponseInterceptor i: responseLast) {
b.addLast(i);
}
}
httpprocessorCopy = b.build();
}
execChain = new ProtocolExec(execChain, httpprocessorCopy);
execChain = decorateProtocolExec(execChain);
// Add request retry executor, if not disabled
if (!automaticRetriesDisabled) {
HttpRequestRetryHandler retryHandlerCopy = this.retryHandler;
if (retryHandlerCopy == null) {
retryHandlerCopy = DefaultHttpRequestRetryHandler.INSTANCE;
}
execChain = new RetryExec(execChain, retryHandlerCopy);
}
HttpRoutePlanner routePlannerCopy = this.routePlanner;
if (routePlannerCopy == null) {
SchemePortResolver schemePortResolverCopy = this.schemePortResolver;
if (schemePortResolverCopy == null) {
schemePortResolverCopy = DefaultSchemePortResolver.INSTANCE;
}
if (proxy != null) {
routePlannerCopy = new DefaultProxyRoutePlanner(proxy, schemePortResolverCopy);
} else if (systemProperties) {
routePlannerCopy = new SystemDefaultRoutePlanner(
schemePortResolverCopy, ProxySelector.getDefault());
} else {
routePlannerCopy = new DefaultRoutePlanner(schemePortResolverCopy);
}
}
// Optionally, add service unavailable retry executor
final ServiceUnavailableRetryStrategy serviceUnavailStrategyCopy = this.serviceUnavailStrategy;
if (serviceUnavailStrategyCopy != null) {
execChain = new ServiceUnavailableRetryExec(execChain, serviceUnavailStrategyCopy);
}
// Add redirect executor, if not disabled
if (!redirectHandlingDisabled) {
RedirectStrategy redirectStrategyCopy = this.redirectStrategy;
if (redirectStrategyCopy == null) {
redirectStrategyCopy = DefaultRedirectStrategy.INSTANCE;
}
execChain = new RedirectExec(execChain, routePlannerCopy, redirectStrategyCopy);
}
// Optionally, add connection back-off executor
if (this.backoffManager != null && this.connectionBackoffStrategy != null) {
execChain = new BackoffStrategyExec(execChain, this.connectionBackoffStrategy, this.backoffManager);
}
Lookup<AuthSchemeProvider> authSchemeRegistryCopy = this.authSchemeRegistry;
if (authSchemeRegistryCopy == null) {
authSchemeRegistryCopy = RegistryBuilder.<AuthSchemeProvider>create()
.register(AuthSchemes.BASIC, new BasicSchemeFactory())
.register(AuthSchemes.DIGEST, new DigestSchemeFactory())
.register(AuthSchemes.NTLM, new NTLMSchemeFactory())
.register(AuthSchemes.SPNEGO, new SPNegoSchemeFactory())
.register(AuthSchemes.KERBEROS, new KerberosSchemeFactory())
.build();
}
Lookup<CookieSpecProvider> cookieSpecRegistryCopy = this.cookieSpecRegistry;
if (cookieSpecRegistryCopy == null) {
cookieSpecRegistryCopy = CookieSpecRegistries.createDefault(publicSuffixMatcherCopy);
}
CookieStore defaultCookieStore = this.cookieStore;
if (defaultCookieStore == null) {
defaultCookieStore = new BasicCookieStore();
}
CredentialsProvider defaultCredentialsProvider = this.credentialsProvider;
if (defaultCredentialsProvider == null) {
if (systemProperties) {
defaultCredentialsProvider = new SystemDefaultCredentialsProvider();
} else {
defaultCredentialsProvider = new BasicCredentialsProvider();
}
}
List<Closeable> closeablesCopy = closeables != null ? new ArrayList<Closeable>(closeables) : null;
if (!this.connManagerShared) {
if (closeablesCopy == null) {
closeablesCopy = new ArrayList<Closeable>(1);
}
final HttpClientConnectionManager cm = connManagerCopy;
if (evictExpiredConnections || evictIdleConnections) {
final IdleConnectionEvictor connectionEvictor = new IdleConnectionEvictor(cm,
maxIdleTime > 0 ? maxIdleTime : 10, maxIdleTimeUnit != null ? maxIdleTimeUnit : TimeUnit.SECONDS);
closeablesCopy.add(new Closeable() {
@Override
public void close() throws IOException {
connectionEvictor.shutdown();
}
});
connectionEvictor.start();
}
closeablesCopy.add(new Closeable() {
@Override
public void close() throws IOException {
cm.shutdown();
}
});
}
return new InternalHttpClient(
execChain,
connManagerCopy,
routePlannerCopy,
cookieSpecRegistryCopy,
authSchemeRegistryCopy,
defaultCookieStore,
defaultCredentialsProvider,
defaultRequestConfig != null ? defaultRequestConfig : RequestConfig.DEFAULT,
closeablesCopy);
}我们可以看到他这个的实现是非常复杂的，我们来看execute方法：
他是一个抽象类，具体的实现在子类：
@Override
protected final CloseableHttpResponse doExecute(final HttpHost target, final HttpRequest request,
final HttpContext context)
throws IOException, ClientProtocolException {
Args.notNull(request, "HTTP request");
// a null target may be acceptable, this depends on the route planner
// a null context is acceptable, default context created below
HttpContext execContext = null;
RequestDirector director = null;
HttpRoutePlanner routePlanner = null;
ConnectionBackoffStrategy connectionBackoffStrategy = null;
BackoffManager backoffManager = null;
// Initialize the request execution context making copies of
// all shared objects that are potentially threading unsafe.
synchronized (this) {
final HttpContext defaultContext = createHttpContext();
if (context == null) {
execContext = defaultContext;
} else {
execContext = new DefaultedHttpContext(context, defaultContext);
}
final HttpParams params = determineParams(request);
final RequestConfig config = HttpClientParamConfig.getRequestConfig(params);
execContext.setAttribute(ClientContext.REQUEST_CONFIG, config);
// Create a director for this request
director = createClientRequestDirector(
getRequestExecutor(),
getConnectionManager(),
getConnectionReuseStrategy(),
getConnectionKeepAliveStrategy(),
getRoutePlanner(),
getProtocolProcessor(),
getHttpRequestRetryHandler(),
getRedirectStrategy(),
getTargetAuthenticationStrategy(),
getProxyAuthenticationStrategy(),
getUserTokenHandler(),
params);
routePlanner = getRoutePlanner();
connectionBackoffStrategy = getConnectionBackoffStrategy();
backoffManager = getBackoffManager();
}
try {
if (connectionBackoffStrategy != null && backoffManager != null) {
final HttpHost targetForRoute = (target != null) ? target
: (HttpHost) determineParams(request).getParameter(
ClientPNames.DEFAULT_HOST);
final HttpRoute route = routePlanner.determineRoute(targetForRoute, request, execContext);
final CloseableHttpResponse out;
try {
out = CloseableHttpResponseProxy.newProxy(
director.execute(target, request, execContext));
} catch (final RuntimeException re) {
if (connectionBackoffStrategy.shouldBackoff(re)) {
backoffManager.backOff(route);
}
throw re;
} catch (final Exception e) {
if (connectionBackoffStrategy.shouldBackoff(e)) {
backoffManager.backOff(route);
}
if (e instanceof HttpException) {
throw (HttpException)e;
}
if (e instanceof IOException) {
throw (IOException)e;
}
throw new UndeclaredThrowableException(e);
}
if (connectionBackoffStrategy.shouldBackoff(out)) {
backoffManager.backOff(route);
} else {
backoffManager.probe(route);
}
return out;
} else {
return CloseableHttpResponseProxy.newProxy(
director.execute(target, request, execContext));
}
} catch(final HttpException httpException) {
throw new ClientProtocolException(httpException);
}
}这个是他里边的一个实现，可以看出来，也是非常复杂的。HttpClient Get的请求大概就这么多，想深入的同学可以去仔细研究源码。
有问题可以在下面评论，技术问题可以私聊我。