转：java网络编程-HTTP编程

转自：

java网络编程-HTTP编程_Stillsings的博客-CSDN博客HTTP编程Java HTTP编程支持模拟成浏览器的方式去访问网页URL, Uniform Resource Locator，代表一个资源URLConnection获取资源连接器根据URL的openConnection（）方法获得URLConnectionconnect方法，建立和资源的联系通道getInputStream方法，获取资源的内容示例代码：Get获取网页h...https://blog.csdn.net/Listen_heart/article/details/104448012

---

【1】HTTP编程

Java HTTP编程

    支持模拟成浏览器的方式去访问网页
    URL, Uniform Resource Locator，代表一个资源
    URLConnection
        获取资源连接器
        根据URL的openConnection（）方法获得URLConnection
        connect方法，建立和资源的联系通道
        getInputStream方法，获取资源的内容

【2】URLConnection

示例代码1：Get获取网页html-使用URLConnection

package com.lihuan.network.demo03;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLConnection;
import java.nio.charset.StandardCharsets;
import java.util.List;
import java.util.Map;

public class URLConnectionGetTest {
    public static void main(String[] args) {
        try {
            String urlName = "http://www.baidu.com";
            URL url = new URL(urlName);
            URLConnection connection = url.openConnection();
            //建立联系通道
            connection.connect();

            //打印http的头部信息
            Map<String, List<String>> headers = connection.getHeaderFields();
            for (Map.Entry<String, List<String>> entry : headers.entrySet()){
                String key = entry.getKey();
                for (String value : entry.getValue()){
                    System.out.println(key + ":" + value);
                }
            }

            //输出将要收到的内容属性信息

            System.out.println("-------------");
            System.out.println("getContentType: " + connection.getContentType());
            System.out.println("getContentLength: " + connection.getContentLength());
            System.out.println("getContentEncoding: " + connection.getContentEncoding());
            System.out.println("getDate: " + connection.getDate());
            System.out.println("getExpiration: " + connection.getExpiration());
            System.out.println("getLastModified:" + connection.getLastModified());
            System.out.println("-------------");

            BufferedReader br = new BufferedReader(new InputStreamReader(connection.getInputStream(), StandardCharsets.UTF_8));

            // 输出收到的内容

            String line = "";
            while ((line = br.readLine()) != null){
                System.out.println(line);
            }

            br.close();
        } catch (IOException e) {
            e.printStackTrace();
        }

    }
}

---

实例代码2： Post提交表单-使用 HttpURLConnection

package com.lihuan.network.demo03;

import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.net.*;
import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;

public class URLConnectionPostTest {
    public static void main(String[] args) throws IOException {
        String urlString = "https://tools.usps.com/zip-code-lookup.htm?byaddress";
        Object userAgent = "HTTPie/0.9.2";
        Object redirects = "1";
        CookieHandler.setDefault(new CookieManager(null, CookiePolicy.ACCEPT_ALL));

        Map<String, String> params = new HashMap<String, String>();
        params.put("tAddress", "1 Market Street");
        params.put("tCity", "san Francisco");
        params.put("sState", "CA");

        String result = doPost(new URL(urlString), params,
                userAgent == null ? null : userAgent.toString(),
                redirects == null ? -1 : Integer.parseInt(redirects.toString()));

        System.out.println(result);
    }

    public static String doPost(URL url, Map<String, String> nameValuePairs, String userAgent, int redirects) throws IOException {
        HttpURLConnection connection = (HttpURLConnection) url.openConnection();
        //设置请求头
        if(userAgent != null){
            connection.setRequestProperty("User-Agent", userAgent);
        }
        //设为不自动重定向
        if(redirects >= 0){
            connection.setInstanceFollowRedirects(false);
        }
        //设置可以使用conn.getOutputStream().print
        connection.setDoOutput(true);

        //输出请求的参数
        try (PrintWriter out = new PrintWriter(connection.getOutputStream())){
            boolean first = true;
            for (Map.Entry<String, String> pair : nameValuePairs.entrySet()){
                //参数拼接
                if(first){
                    first = false;
                }else{
                    out.print('&');
                }
                String name = pair.getKey();
                String value = pair.getValue();
                out.print(name);
                out.print("=");
                out.print(URLEncoder.encode(value, "UTF-8"));
            }
        }
        String encoding = connection.getContentEncoding();
        if(encoding == null){
            encoding = "UTF-8";
        }
        if(redirects > 0){
            int responseCode = connection.getResponseCode();
            System.out.println("responseCode: " + responseCode);
            if(responseCode == HttpURLConnection.HTTP_MOVED_PERM
                    || responseCode == HttpURLConnection.HTTP_MOVED_TEMP
                    || responseCode == HttpURLConnection.HTTP_SEE_OTHER){
                String location = connection.getHeaderField("Location");
                if(location != null){
                    URL base = connection.getURL();
                    connection.disconnect();
                    return doPost(new URL(base, location), nameValuePairs, userAgent, redirects - 1);
                }
            }
        }else if(redirects == 0){
            throw new IOException("Too many redirects");
        }

        //接下来获取html内容
        StringBuilder response = new StringBuilder();
        try (Scanner in = new Scanner(connection.getInputStream(), encoding)){
            while (in.hasNextLine()){
                response.append(in.nextLine());
                response.append("\n");
            }
        }catch (IOException e){
            InputStream err = connection.getErrorStream();
            if(err == null) throw e;
            try (Scanner in = new Scanner(err)){
                response.append(in.nextLine());
                response.append("\n");
            }
        }
        return response.toString();
    }
}

---

【3】JDK HttpClient

    JDK 9新增，JDK10更新，JDK11正式发
    java.net.http包
    取代URLConnection
    支持HTTP/1.1和HTTP/2
    实现大部分HTTP方法
    主要类
        HttpClient
        HttpRequest
        HttpResponse

HttpComponents

    是一个集成的Java HTTP工具包
    实现所有HTTP方法: get/post/put/delete
    支持自动转向
    支持https协议
    支持代理服务器等

HttpComponent示例代码3：Get获取网页html

package com.lihuan.network.demo04;

import org.apache.http.HttpResponse;
import org.apache.http.client.config.RequestConfig;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.util.EntityUtils;

import java.io.IOException;

public class HttpComponentGetTest {
    public static void main(String[] args) {
        CloseableHttpClient httpClient = HttpClients.createDefault();
        RequestConfig requestConfig = RequestConfig.custom()
                .setConnectTimeout(5000)
                .setConnectionRequestTimeout(5000)
                .setSocketTimeout(5000)
                .setRedirectsEnabled(true)
                .build();
        HttpGet httpGet = new HttpGet("http://www.baidu.com");
        httpGet.setConfig(requestConfig);
        String strResult = "";
        try {
            HttpResponse httpResponse = httpClient.execute(httpGet);
            if(httpResponse.getStatusLine().getStatusCode() == 200){
                strResult = EntityUtils.toString(httpResponse.getEntity(), "UTF-8");
                System.out.println(strResult);
            }else{

            }
        } catch (IOException e) {
            e.printStackTrace();
        }finally {
            try {
                httpClient.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

HttpComponent实例代码4：Post提交表单

package com.lihuan.network.demo04;

import org.apache.http.HttpResponse;
import org.apache.http.client.config.RequestConfig;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClientBuilder;
import org.apache.http.impl.client.LaxRedirectStrategy;
import org.apache.http.message.BasicNameValuePair;
import org.apache.http.util.EntityUtils;

import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.net.URLEncoder;
import java.util.ArrayList;
import java.util.List;

public class HttpComponentsPostTest {
    public static void main(String[] args) throws UnsupportedEncodingException {
        //获取可关闭的 httpClient
        CloseableHttpClient httpClient = HttpClientBuilder.create().setRedirectStrategy(new LaxRedirectStrategy()).build();

        //配置超时时间
        RequestConfig requestConfig = RequestConfig.custom()
                .setConnectTimeout(10000).setConnectionRequestTimeout(10000)
                .setSocketTimeout(10000).setRedirectsEnabled(false).build();

        HttpPost httpPost = new HttpPost("https://tools.usps.com/zip-code-lookup.htm?byaddress");
        //设置超时时间
        httpPost.setConfig(requestConfig);

        List<BasicNameValuePair> list = new ArrayList<>();
        list.add(new BasicNameValuePair("tAddress", URLEncoder.encode("1 Market Street", "UTF-8")));
        list.add(new BasicNameValuePair("tCity", URLEncoder.encode("san Francisco", "UTF-8")));
        list.add(new BasicNameValuePair("sState", "CA"));

        try {
            UrlEncodedFormEntity entity = new UrlEncodedFormEntity(list, "UTF-8");
            //设置post请求参数
            httpPost.setEntity(entity);
            httpPost.setHeader("User-Agent", "HTTPie/0.9.2");
            HttpResponse httpResponse = httpClient.execute(httpPost);
            String strResult = "";
            if(httpResponse != null){
                System.out.println(httpResponse.getStatusLine().getStatusCode());
                if(httpResponse.getStatusLine().getStatusCode() == 200){
                    strResult = EntityUtils.toString(httpResponse.getEntity());
                }else{
                    strResult = "Error Response：" + httpResponse.getStatusLine().toString();
                }
            }else{

            }
            System.out.println(strResult);
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if(httpClient != null){
                try {
                    httpClient.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}