java 图片下载

java 图片下载

工作中遇到图片下载，有时候成功，有时候失败；排查后发现 http 协议的下载成功，https 格式的下载不成功，考虑是因为服务器没有安全证书的原因。后面上面说直接去除掉 https 的安全校验

• http 协议图片下载

• 去除 https 协议的安全校验

• 图片编码为 base64 字符串

• 只基于依赖 jdk 和 spring

/**
 * @author 
 * @date 2023/11/29
 */

import org.apache.commons.lang3.ObjectUtils;
import org.apache.commons.lang3.StringUtils;
import org.springframework.util.Base64Utils;
import javax.net.ssl.HttpsURLConnection;
import javax.net.ssl.SSLContext;
import javax.net.ssl.TrustManager;
import javax.net.ssl.X509TrustManager;
import java.io.BufferedInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLConnection;
import java.security.KeyManagementException;
import java.security.NoSuchAlgorithmException;
import java.security.cert.CertificateException;
import java.security.cert.X509Certificate;
import java.util.Objects;

/**
 * 网络连接工具
 */
public class NetUtils {
    /**
     * 更具 url 下载图片，转成 base64字符串（只支持 http 和 https）
     * @param url
     * @return
     * @throws IOException
     */
    public static String downloadImgToBase64(String url) throws IOException, NoSuchAlgorithmException, KeyManagementException {
        URLConnection connection = buildURLConnection(url);
        return downloadImgToBase64(connection);
    }

    /**
     * 下载图片，转成 base64字符串
     * @param connection
     * @return
     * @throws IOException
     */
    public static String downloadImgToBase64(URLConnection connection) throws IOException {
        String base64Img = null;

        if (Objects.isNull(connection)) {
            return base64Img;
        }

        // 下载图片到内存。用字节数组接收
        try (
                InputStream inputStream = new BufferedInputStream(connection.getInputStream());
                ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
        ) {
            byte[] buffer = new byte[1024];
            int bytesRead;
            while ((bytesRead = inputStream.read(buffer)) != -1) {
                outputStream.write(buffer, 0, bytesRead);
            }
            byte[] byteArray = outputStream.toByteArray();
            base64Img = Base64Utils.encodeToString(byteArray);
        }
        return base64Img;
    }

    /**
     * 根据协议创建连接对象
     * @param url
     * @return
     * @throws IOException
     * @throws NoSuchAlgorithmException
     * @throws KeyManagementException
     */
    public static URLConnection buildURLConnection(String url) throws IOException, NoSuchAlgorithmException, KeyManagementException {
        if (StringUtils.isBlank(url)) {
            return null;
        }
        // 创建连接对象
        URL urlObject = new URL(url);
        String protocol = urlObject.getProtocol();

        URLConnection connection = null;
        if ("http".equals(protocol)) {
            connection = buildHttpConnection(urlObject);
        }else if ("https".equals(protocol)){
            connection =  buildUnsafeHttpsConnection(urlObject);
        }

        return connection;
    }

    /**
     * 根据给定的url 建立http连接。如果是https 请求，忽略证书校验
     * @param url
     * @return
     */
    public static HttpsURLConnection buildUnsafeHttpsConnection(URL url) throws IOException, NoSuchAlgorithmException, KeyManagementException {
        if (Objects.isNull(url)) {
            return null;
        }
        // 创建连接对象
        HttpsURLConnection connection = (HttpsURLConnection) url.openConnection();

        // 忽略证书校验
        connection.setHostnameVerifier((hostname,session) -> true);
        SSLContext sslContext = SSLContext.getInstance("TLS");
        sslContext.init(null,new TrustManager[]{new X509TrustManager() {
            public void checkClientTrusted(X509Certificate[] certs, String authType) throws CertificateException {
            }

            public void checkServerTrusted(X509Certificate[] certs, String authType) throws CertificateException {
            }

            public X509Certificate[] getAcceptedIssuers() {
                return new X509Certificate[]{};
            }
        }}, new java.security.SecureRandom());
        connection.setSSLSocketFactory(sslContext.getSocketFactory());

        return connection;
    }

    /**
     * 根据给定的url 建立http连接
     * @param url
     * @return
     * @throws MalformedURLException
     */
    public static HttpURLConnection buildHttpConnection(URL url) throws IOException {
        if (ObjectUtils.isEmpty(url)) {
            return null;
        }

        HttpURLConnection connection = (HttpURLConnection)url.openConnection();
        return connection;
    }
}