最近項(xiàng)目需要使用 Java 重度調(diào)用 HTTP API 接口，于是想著封裝一個(gè)團(tuán)隊(duì)公用的 HTTP client lib. 這個(gè)庫(kù)需要支持以下特性：
連接池管理，包括連接創(chuàng)建和超時(shí)、空閑連接數(shù)控制、每個(gè) host 的連接數(shù)配置等。基本上，我們想要一個(gè) go HTTP 標(biāo)準(zhǔn)庫(kù)自帶的連接池管理功能。
域名解析控制。因?yàn)檎{(diào)用量會(huì)比較大，因此希望在域名解析這一層做一個(gè)調(diào)用端可控的負(fù)載均衡，同時(shí)可以對(duì)每個(gè)服務(wù)器 IP 進(jìn)行失敗率統(tǒng)計(jì)和健康度檢查。
Form/JSON 調(diào)用支持良好。
支持同步和異步調(diào)用。
在 Java 生態(tài)中，雖然有數(shù)不清的 HTTP client lib 組件庫(kù)，但是大體可以分為這三類：
JDK 自帶的?HttpURLConnection?標(biāo)準(zhǔn)庫(kù)；
Apache HttpComponents HttpClient, 以及基于該庫(kù)的 wrapper, 如?Unirest.
非基于 Apache HttpComponents HttpClient， 大量重寫(xiě)應(yīng)用層代碼的 HTTP client 組件庫(kù)，典型代表是?OkHttp.
HttpURLConnection
使用 HttpURLConnection 發(fā)起 HTTP 請(qǐng)求最大的優(yōu)點(diǎn)是不需要引入額外的依賴，但是使用起來(lái)非常繁瑣，也缺乏連接池管理、域名機(jī)械控制等特性支持。以發(fā)起一個(gè) HTTP POST 請(qǐng)求為例：
import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.URL;
public class HttpUrlConnectionDemo {
????public static void main(String[] args) throws Exception {
????????String urlString = "https://httpbin.org/post";
????????String bodyString = "password=e10adc3949ba59abbe56e057f20f883e&username=test3";
????????URL url = new URL(urlString);
????????HttpURLConnection conn = (HttpURLConnection) url.openConnection();
????????conn.setRequestMethod("POST");
????????conn.setDoOutput(true);
????????OutputStream os = conn.getOutputStream();
????????os.write(bodyString.getBytes("utf-8"));
????????os.flush();
????????os.close();
????????if (conn.getResponseCode() == HttpURLConnection.HTTP_OK) {
????????????InputStream is = conn.getInputStream();
????????????BufferedReader reader = new BufferedReader(new InputStreamReader(is));
????????????StringBuilder sb = new StringBuilder();
????????????String line;
????????????while ((line = reader.readLine()) != null) {
????????????????sb.append(line);
????????????}
????????????System.out.println("rsp:" + sb.toString());
????????} else {
????????????System.out.println("rsp code:" + conn.getResponseCode());
????????}
????}
}
可以看到，使用 HttpURLConnection 發(fā)起 HTTP 請(qǐng)求是比較原始（low level）的，基本上你可以理解為它就是對(duì)網(wǎng)絡(luò)棧傳輸層（HTTP 一般為 TCP，HTTP over QUIC 是 UDP）進(jìn)行了一次淺層次的封裝，操作原語(yǔ)就是在打開(kāi)的連接上面寫(xiě)請(qǐng)求 request 與讀響應(yīng) response. 而且 HttpURLConnection 無(wú)法支持 HTTP/2. 顯然,官方是知道這些問(wèn)題的，因此在 Java 9 中，官方在標(biāo)準(zhǔn)庫(kù)中引入了一個(gè) high level、支持 HTTP/2 的?HttpClient. 這個(gè)庫(kù)的接口封裝就非常主流到位了，發(fā)起一個(gè)簡(jiǎn)單的 POST 請(qǐng)求：
HttpRequest request = HttpRequest.newBuilder()
??.uri(new URI("https://postman-echo.com/post"))
??.headers("Content-Type", "text/plain;charset=UTF-8")
??.POST(HttpRequest.BodyProcessor.fromString("Sample request body"))
??.build();
封裝的最大特點(diǎn)是鏈?zhǔn)秸{(diào)用非常順滑，支持連接管理等特性。但是這個(gè)庫(kù)只能在 Java 9 及以后的版本使用，Java 9 和 Java 10 并不是 LTS 維護(hù)版本，而接下來(lái)的 Java 11 LTS 要在2018.09.25發(fā)布，應(yīng)用到線上還需要等待一段時(shí)間。因此，雖然挺喜歡這個(gè)自帶標(biāo)準(zhǔn)庫(kù)（畢竟可以不引入三方依賴），但當(dāng)前是無(wú)法在生產(chǎn)環(huán)境使用的。
Apache HttpComponents HttpClient
Apache HttpComponents HttpClient 的前身是?Apache Commons HttpClient, 但是 Apache Commons HttpClient 已經(jīng)停止開(kāi)發(fā)，如果你還在使用它，請(qǐng)切換到 Apache HttpComponents HttpClient 上來(lái)。
Apache HttpComponents HttpClient 支持的特性非常豐富，完全覆蓋我們的需求，使用起來(lái)也非常順手：
<br />import java.io.ByteArrayOutputStream;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import org.apache.commons.io.IOUtils;
import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.fluent.Request;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.client.methods.RequestBuilder;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.message.BasicNameValuePair;
import org.apache.http.impl.client.HttpClients;
public class HttpComponentsDemo {
????final static CloseableHttpClient client = HttpClients.createDefault();
????// 常規(guī)調(diào)用
????private String sendPostForm(String url, Map<String, String> params) throws Exception {
????????HttpPost request = new HttpPost(url);
????????// set header
????????request.setHeader("X-Http-Demo", HttpComponentsDemo.class.getSimpleName());
????????// set params
????????if (params != null) {
????????????List<NameValuePair> nameValuePairList = new ArrayList<NameValuePair>();
????????????for (Map.Entry<String, String> entry : params.entrySet()) {
????????????????nameValuePairList.add(new BasicNameValuePair(entry.getKey(), entry.getValue()));
????????????}
????????????UrlEncodedFormEntity bodyEntity = new UrlEncodedFormEntity(nameValuePairList, "UTF-8");
????????????//System.out.println("body:" + IOUtils.toString(bodyEntity.getContent()));
????????????request.setEntity(new UrlEncodedFormEntity(nameValuePairList));
????????}
????????// send request
????????CloseableHttpResponse response = client.execute(request);
????????// read rsp code
????????System.out.println("rsp code:" + response.getStatusLine().getStatusCode());
????????// return content
????????String ret = readResponseContent(response.getEntity().getContent());
????????response.close();
????????return ret;
????}
????// fluent 鏈?zhǔn)秸{(diào)用
????private String sendGet(String url) throws Exception {
????????return Request.Get(url)
????????????????.connectTimeout(1000)
????????????????.socketTimeout(1000)
????????????????.execute().returnContent().asString();
????}
????private String readResponseContent(InputStream inputStream) throws Exception {
????????if (inputStream == null) {
????????????return "";
????????}
????????ByteArrayOutputStream out = new ByteArrayOutputStream();
????????byte[] buf = new byte[512];
????????int len;
????????while (inputStream.available() > 0) {
????????????len = inputStream.read(buf);
????????????out.write(buf, 0, len);
????????}
????????return out.toString();
????}
????public static void main(String[] args) throws Exception {
????????HttpComponentsDemo httpUrlConnectionDemo = new HttpComponentsDemo();
????????String url = "https://httpbin.org/post";
????????Map<String, String> params = new HashMap<String, String>();
????????params.put("foo", "bar中文");
????????String rsp = httpUrlConnectionDemo.sendPostForm(url, params);
????????System.out.println("http post rsp:" + rsp);
????????url = "https://httpbin.org/get";
????????System.out.println("http get rsp:" + httpUrlConnectionDemo.sendGet(url));
????}
}
對(duì) Client 細(xì)致的配置和自定義支持也是非常到位的：
????????// Create a connection manager with custom configuration.
????????PoolingHttpClientConnectionManager connManager = new PoolingHttpClientConnectionManager(
????????????????socketFactoryRegistry, connFactory, dnsResolver);
????????// Create socket configuration
????????SocketConfig socketConfig = SocketConfig.custom()
????????????.setTcpNoDelay(true)
????????????.build();
????????// Configure the connection manager to use socket configuration either
????????// by default or for a specific host.
????????connManager.setDefaultSocketConfig(socketConfig);
????????connManager.setSocketConfig(new HttpHost("somehost", 80), socketConfig);
????????// Validate connections after 1 sec of inactivity
????????connManager.setValidateAfterInactivity(1000);
????????// Create message constraints
????????MessageConstraints messageConstraints = MessageConstraints.custom()
????????????.setMaxHeaderCount(200)
????????????.setMaxLineLength(2000)
????????????.build();
????????// Create connection configuration
????????ConnectionConfig connectionConfig = ConnectionConfig.custom()
????????????.setMalformedInputAction(CodingErrorAction.IGNORE)
????????????.setUnmappableInputAction(CodingErrorAction.IGNORE)
????????????.setCharset(Consts.UTF_8)
????????????.setMessageConstraints(messageConstraints)
????????????.build();
????????// Configure the connection manager to use connection configuration either
????????// by default or for a specific host.
????????connManager.setDefaultConnectionConfig(connectionConfig);
????????connManager.setConnectionConfig(new HttpHost("somehost", 80), ConnectionConfig.DEFAULT);
????????// Configure total max or per route limits for persistent connections
????????// that can be kept in the pool or leased by the connection manager.
????????connManager.setMaxTotal(100);
????????connManager.setDefaultMaxPerRoute(10);
????????connManager.setMaxPerRoute(new HttpRoute(new HttpHost("somehost", 80)), 20);
完整示例請(qǐng)參考?ClientConfiguration.
基本上，在 Java 原生標(biāo)準(zhǔn)庫(kù)不給力的情況下，Apache HttpComponents HttpClient 是最佳的 HTTP Client library 選擇。但這個(gè)庫(kù)當(dāng)前還不支持 HTTP/2，支持 HTTP/2 的版本還處于 beta 階段（2018.09.23），因此并不適合用于 Android APP 中使用。
OkHttp
由于當(dāng)前 Apache HttpComponents HttpClient 版本并不支持 HTTP/2, 而 HTTP/2 對(duì)于移動(dòng)客戶端而言，無(wú)論是從握手延遲、響應(yīng)延遲，還是資源開(kāi)銷看都有相當(dāng)吸引力。因此這就給了高層次封裝且支持 HTTP/2 的 http client lib 足夠的生存空間。其中最典型的要數(shù)OkHttp.
<br /><br />import okhttp3.*;
import org.apache.http.util.CharsetUtils;
import java.util.HashMap;
import java.util.Map;
public class OkHttpDemo {
????OkHttpClient client = new OkHttpClient();
????private String sendPostForm(String url, final Map<String, String> params) throws Exception {
????????FormBody.Builder builder = new FormBody.Builder(CharsetUtils.get("UTF-8"));
????????if (params != null) {
????????????for (Map.Entry<String, String> entry: params.entrySet()) {
????????????????builder.add(entry.getKey(), entry.getValue());
????????????}
????????}
????????RequestBody requestBody = builder.build();
????????Request request = new Request.Builder().url(url).post(requestBody).build();
????????return client.newCall(request).execute().body().string();
????}
????private String sendGet(String url) throws Exception {
????????Request request = new Request.Builder().url(url).build();
????????return??client.newCall(request).execute().body().string();
????}
????public static void main(String[] args) throws Exception {
????????OkHttpDemo okHttpDemo = new OkHttpDemo();
????????String url = "https://httpbin.org/post";
????????Map<String, String> params = new HashMap<String, String>();
????????params.put("foo", "bar中文");
????????String rsp = okHttpDemo.sendPostForm(url, params);
????????System.out.println("http post rsp:" + rsp);
????????url = "https://httpbin.org/get";
????????System.out.println("http get rsp:" + okHttpDemo.sendGet(url));
????}
}
OkHttp 接口設(shè)計(jì)友好，支持 HTTP/2，并且在弱網(wǎng)和無(wú)網(wǎng)環(huán)境下有自動(dòng)檢測(cè)和恢復(fù)機(jī)制，因此，是當(dāng)前 Android APP 開(kāi)發(fā)中使用最廣泛的 HTTP clilent lib 之一。
另一方面，OkHttp 提供的接口與 Java 9 中 HttpClint 接口比較類似 （嚴(yán)格講，應(yīng)該是 Java 9 借鑒了 OkHttp 等開(kāi)源庫(kù)的接口設(shè)計(jì)？），因此，對(duì)于喜歡減少依賴，鐘情于原生標(biāo)準(zhǔn)庫(kù)的開(kāi)發(fā)者來(lái)說(shuō)，在 Java 11 中，從 OkHttp 切換到標(biāo)準(zhǔn)庫(kù)是相對(duì)容易的。因此，以 OkHttp 為代表的 http 庫(kù)以后的使用場(chǎng)景可能會(huì)被蠶食一部分。
小結(jié)
HttpURLConnection 封裝層次太低，并且支持特性太少，不建議在項(xiàng)目中使用。除非你的確不想引入第三方 HTTP 依賴（如減少包大小、目標(biāo)環(huán)境不提供三方庫(kù)支持等）。
Java 9 中引入的 HttpClient，封裝層次和支持特性都不錯(cuò)。但是因?yàn)?Java 版本的原因，應(yīng)用場(chǎng)景還十分有限，建議觀望一段時(shí)間再考慮在線上使用。
如果你不需要 HTTP/2特性，Apache HttpComponents HttpClient 是你的最佳選擇，比如在服務(wù)器之間的 HTTP 調(diào)用。否則，請(qǐng)使用 OkHttp, 如 Android 開(kāi)發(fā)。
