Java HTTP 组件库选型看这篇就够了

最近项目需要使用 Java 重度调用 HTTP API 接口，于是想着封装一个团队公用的 HTTP client lib. 这个库需要支持以下特性：

连接池管理，包括连接创建和超时、空闲连接数控制、每个 host 的连接数配置等。基本上，我们想要一个 go HTTP 标准库自带的连接池管理功能。
域名解析控制。因为调用量会比较大，因此希望在域名解析这一层做一个调用端可控的负载均衡，同时可以对每个服务器 IP 进行失败率统计和健康度检查。
Form/JSON 调用支持良好。
支持同步和异步调用。

在 Java 生态中，虽然有数不清的 HTTP client lib 组件库，但是大体可以分为这三类：

JDK 自带的 HttpURLConnection 标准库；
Apache HttpComponents HttpClient, 以及基于该库的 wrapper, 如 Unirest.
非基于 Apache HttpComponents HttpClient，大量重写应用层代码的 HTTP client 组件库，典型代表是 OkHttp.

HttpURLConnection

使用 HttpURLConnection 发起 HTTP 请求最大的优点是不需要引入额外的依赖，但是使用起来非常繁琐，也缺乏连接池管理、域名机械控制等特性支持。以发起一个 HTTP POST 请求为例：

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&amp;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());
        }
    }

}

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 发起 HTTP 请求是比较原始（low level）的，基本上你可以理解为它就是对网络栈传输层（HTTP 一般为 TCP，HTTP over QUIC 是 UDP）进行了一次浅层次的封装，操作原语就是在打开的连接上面写请求 request 与读响应 response. 而且 HttpURLConnection 无法支持 HTTP/2. 显然,官方是知道这些问题的，因此在 Java 9 中，官方在标准库中引入了一个 high level、支持 HTTP/2 的 HttpClient. 这个库的接口封装就非常主流到位了，发起一个简单的 POST 请求：

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();

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();

封装的最大特点是链式调用非常顺滑，支持连接管理等特性。但是这个库只能在 Java 9 及以后的版本使用，Java 9 和 Java 10 并不是 LTS 维护版本，而接下来的 Java 11 LTS 要在2018.09.25发布，应用到线上还需要等待一段时间。因此，虽然挺喜欢这个自带标准库（毕竟可以不引入三方依赖），但当前是无法在生产环境使用的。

Apache HttpComponents HttpClient

Apache HttpComponents HttpClient 的前身是 Apache Commons HttpClient, 但是 Apache Commons HttpClient 已经停止开发，如果你还在使用它，请切换到 Apache HttpComponents HttpClient 上来。

Apache HttpComponents HttpClient 支持的特性非常丰富，完全覆盖我们的需求，使用起来也非常顺手：

<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();

    // 常规调用
    private String sendPostForm(String url, Map&lt;String, String&gt; params) throws Exception {
        HttpPost request = new HttpPost(url);

        // set header
        request.setHeader("X-Http-Demo", HttpComponentsDemo.class.getSimpleName());

        // set params
        if (params != null) {
            List&lt;NameValuePair&gt; nameValuePairList = new ArrayList&lt;NameValuePair&gt;();
            for (Map.Entry&lt;String, String&gt; 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 链式调用
    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() &gt; 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&lt;String, String&gt; params = new HashMap&lt;String, String&gt;();
        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));
    }
}

<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();

// 常规调用

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 链式调用

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));

}

对 Client 细致的配置和自定义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);

// 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);

完整示例请参考 ClientConfiguration.

基本上，在 Java 原生标准库不给力的情况下，Apache HttpComponents HttpClient 是最佳的 HTTP Client library 选择。但这个库当前还不支持 HTTP/2，支持 HTTP/2 的版本还处于 beta 阶段（2018.09.23），因此并不适合用于 Android APP 中使用。

OkHttp

由于当前 Apache HttpComponents HttpClient 版本并不支持 HTTP/2, 而 HTTP/2 对于移动客户端而言，无论是从握手延迟、响应延迟，还是资源开销看都有相当吸引力。因此这就给了高层次封装且支持 HTTP/2 的 http client lib 足够的生存空间。其中最典型的要数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&lt;String, String&gt; params) throws Exception {
        FormBody.Builder builder = new FormBody.Builder(CharsetUtils.get("UTF-8"));
        if (params != null) {
            for (Map.Entry&lt;String, String&gt; 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&lt;String, String&gt; params = new HashMap&lt;String, String&gt;();
        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));
    }
}

<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 接口设计友好，支持 HTTP/2，并且在弱网和无网环境下有自动检测和恢复机制，因此，是当前 Android APP 开发中使用最广泛的 HTTP clilent lib 之一。

另一方面，OkHttp 提供的接口与 Java 9 中 HttpClint 接口比较类似（严格讲，应该是 Java 9 借鉴了 OkHttp 等开源库的接口设计？），因此，对于喜欢减少依赖，钟情于原生标准库的开发者来说，在 Java 11 中，从 OkHttp 切换到标准库是相对容易的。因此，以 OkHttp 为代表的 http 库以后的使用场景可能会被蚕食一部分。

小结

HttpURLConnection 封装层次太低，并且支持特性太少，不建议在项目中使用。除非你的确不想引入第三方 HTTP 依赖（如减少包大小、目标环境不提供三方库支持等）。
Java 9 中引入的 HttpClient，封装层次和支持特性都不错。但是因为 Java 版本的原因，应用场景还十分有限，建议观望一段时间再考虑在线上使用。
如果你不需要 HTTP/2特性，Apache HttpComponents HttpClient 是你的最佳选择，比如在服务器之间的 HTTP 调用。否则，请使用 OkHttp, 如 Android 开发。

扩展阅读

–EOF–

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行思錄 | Travel Coder

Arch, Coding, Life

Java HTTP 组件库选型看这篇就够了

Java HTTP 组件库选型看这篇就够了

HttpURLConnection

Apache HttpComponents HttpClient

OkHttp

小结

扩展阅读