在Java项目中请求HTTPS时，可能会遇到 "unable to find valid certification path to requested target" 错误。这个错误通常是由于SSL证书问题引起的。要解决此问题，可以尝试以下方法

1.忽略SSL验证

        OkHttpClient封装请求

public static OkHttpClient getUnsafeOkHttpClient() {
        try {
            // 创建一个信任所有证书的TrustManager
            final TrustManager[] trustAllCerts = new TrustManager[]{
                    new X509TrustManager() {
                        @Override
                        public void checkClientTrusted(X509Certificate[] chain, String authType) throws CertificateException {
                        }
                        @Override
                        public void checkServerTrusted(X509Certificate[] chain, String authType) throws CertificateException {
                        }
                        @Override
                        public X509Certificate[] getAcceptedIssuers() {
                            return new X509Certificate[0];
                        }
                    }
            };
            // 创建一个不验证证书的 SSLContext，并使用上面的TrustManager初始化
            SSLContext sslContext = SSLContext.getInstance("SSL");
            sslContext.init(null, trustAllCerts, new java.security.SecureRandom());
            // 使用上面创建的SSLContext创建一个SSLSocketFactory
            javax.net.ssl.SSLSocketFactory sslSocketFactory = sslContext.getSocketFactory();
            OkHttpClient.Builder builder = new OkHttpClient.Builder();
            builder.sslSocketFactory(sslSocketFactory, (X509TrustManager) trustAllCerts[0]);
            builder.hostnameVerifier((hostname, session) -> true);
            builder.readTimeout(1, TimeUnit.MINUTES);
            return builder.build();
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }
    public static void main(String[] args) throws Exception {
        
        // 发送请求
        Request request = new Request.Builder()
                .url("https://example.com")
                .build();
        Response response = getUnsafeOkHttpClient().newCall(request).execute();
        System.out.println(response.body().string());
    }

        CloseableHttpClient请求

public static void main(String[] args) throws Exception {
        // 创建SSL上下文，忽略证书验证
        SSLContextBuilder sslContextBuilder = SSLContexts.custom().loadTrustMaterial((chain, authType) -> true);
        SSLConnectionSocketFactory sslSocketFactory = new SSLConnectionSocketFactory(sslContextBuilder.build(), NoopHostnameVerifier.INSTANCE);
        // 创建 CloseableHttpClient 对象
        CloseableHttpClient httpClient = HttpClients.custom()
                .setSSLSocketFactory(sslSocketFactory)
                .build();
        // 创建 HttpGet 对象，并设置请求URL
        HttpGet httpGet = new HttpGet("https://lmg.jj20.com/up/allimg/4k/s/02/2109250006343S5-0-lp.jpg");
        // 设置请求头参数
        httpGet.setHeader("User-Agent", "Mozilla/5.0");
        // 发送请求，获取响应
        HttpResponse response = httpClient.execute(httpGet);
        // 获取响应实体
        HttpEntity entity = response.getEntity();
        // 读取响应内容
        String responseBody = EntityUtils.toString(entity);
        // 输出响应
        System.out.println("Response Code: " + response.getStatusLine().getStatusCode());
        System.out.println("Response Body: " + responseBody);
        // 关闭httpClient
        httpClient.close();
    }

        HttpURLConnection请求

//忽略SSL验证
    public static void ignoreSSL() throws NoSuchAlgorithmException, KeyManagementException {
        SSLContext sslContext = SSLContext.getInstance("TLS");
        TrustManager[] trustManagers = new TrustManager[]{new X509TrustManager() {
            @Override
            public void checkClientTrusted(java.security.cert.X509Certificate[] x509Certificates, String s) {}
            @Override
            public void checkServerTrusted(java.security.cert.X509Certificate[] x509Certificates, String s) {}
            @Override
            public java.security.cert.X509Certificate[] getAcceptedIssuers() {
                return null;
            }
        }};
        sslContext.init(null, trustManagers, new java.security.SecureRandom());
        HttpsURLConnection.setDefaultSSLSocketFactory(sslContext.getSocketFactory());
    }
    public static void main(String[] args) throws Exception {
        ignoreSSL();
        // 创建URL对象
        URL url = new URL("https://lmg.jj20.com/up/allimg/4k/s/02/2109250006343S5-0-lp.jpg");
        // 打开连接
        HttpURLConnection connection = (HttpURLConnection) url.openConnection();
        // 设置请求头参数
        connection.setRequestMethod("GET");
        connection.setRequestProperty("User-Agent", "Mozilla/5.0");
        // 发送请求
        int responseCode = connection.getResponseCode();
        // 读取响应
        BufferedReader reader = new BufferedReader(new InputStreamReader(connection.getInputStream()));
        String line;
        StringBuilder response = new StringBuilder();
        while ((line = reader.readLine()) != null) {
            response.append(line);
        }
        reader.close();
        // 输出响应
        System.out.println("Response Code: " + responseCode);
        System.out.println("Response Body: " + response.toString());
        // 关闭连接
        connection.disconnect();
    }

        RestTemplate请求

public static void ignoreSSL() throws NoSuchAlgorithmException, KeyManagementException {
        SSLContext sslContext = SSLContext.getInstance("TLS");
        TrustManager[] trustManagers = new TrustManager[]{new X509TrustManager() {
            @Override
            public void checkClientTrusted(java.security.cert.X509Certificate[] x509Certificates, String s) {}
            @Override
            public void checkServerTrusted(java.security.cert.X509Certificate[] x509Certificates, String s) {}
            @Override
            public java.security.cert.X509Certificate[] getAcceptedIssuers() {
                return null;
            }
        }};
        sslContext.init(null, trustManagers, new java.security.SecureRandom());
        HttpsURLConnection.setDefaultSSLSocketFactory(sslContext.getSocketFactory());
    }
    public static void main(String str[]) throws Exception{
        ignoreSSL();
        RestTemplate restTemplate = new RestTemplate();
        ResponseEntity response = restTemplate.getForEntity("https://lmg.jj20.com/up/allimg/4k/s/02/2109250006343S5-0-lp.jpg", String.class);
        System.out.println(response.getBody());
    }

2.添加证书到本地证书库

• 获取证书，首先确保您访问的HTTPS网站具有有效的SSL证书。可以通过浏览器访问该网站并查看并导出证书。

   

  • 导入SSL证书：将SSL证书导入到Java的信任存储库中。可以使用keytool命令行工具执行此操作。运行以下命令将证书导入到默认的JDK信任存储库中

    1. keytool -import -alias alias_name -keystore path_to_jdk_cacerts -file path_to_certificate
       -- alias_name 证书指定的别名
       -- path_to_jdk_cacerts是JDK信任存储库的路径，默认路径为$JAVA_HOME/jre/lib/security/cacerts，
       -- path_to_certificate是下载的SSL证书的路径