图片转为为流的处理

方法一：
        response.setContentType("image/png");
//        try {
//            // 步骤 1：创建 URL 对象
//            URL url = new URL(imageUrl);
//
//            // 步骤 2：打开连接
//            HttpURLConnection connection = (HttpURLConnection) url.openConnection();
//            connection.setRequestMethod("GET"); // 设置请求方法为 GET
//
//            // 步骤 3：获取输入流
//            InputStream inputStream = connection.getInputStream();
//            BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream));
//            String line;
//
//            // 读取数据
//            while ((line = reader.readLine()) != null) {
//                System.out.println(line); // 输出获取到的数据
//                //outputStream.write(buffer, 0, bytesRead);
//            }
//            response.setContentType("image/png");
//            //response.setContentType("text/plan");
//            response.getWriter();
//            // 关闭流
//            reader.close();
//            inputStream.close();
//            connection.disconnect();
//        } catch (Exception e) {
//            e.printStackTrace();
//        }



方法二：

if (imageUrl == null || imageUrl.isEmpty()) {
            return;
        }
        InputStream inputStream = null;
        ByteArrayOutputStream outputStream = null;
        try {
            // 禁用SSL证书验证
            TrustManager[] trustAllCerts = new TrustManager[]{new X509TrustManager() {
                @Override
                public java.security.cert.X509Certificate[] getAcceptedIssuers() {
                    return null;
                }

                @Override
                public void checkClientTrusted(java.security.cert.X509Certificate[] certs, String authType) {
                }

                @Override
                public void checkServerTrusted(java.security.cert.X509Certificate[] certs, String authType) {
                }
            }};

// 创建SSLContext，使用禁用SSL证书验证的TrustManager
            SSLContext sslContext = SSLContext.getInstance("SSL");
            sslContext.init(null, trustAllCerts, new java.security.SecureRandom());

// 设置全局默认的SSLSocketFactory，使RestTemplate使用禁用SSL证书验证的SSLContext
            HttpsURLConnection.setDefaultSSLSocketFactory(sslContext.getSocketFactory());


            URL url = new URL(imageUrl);
            URLConnection connection = url.openConnection();
            inputStream = connection.getInputStream();
            outputStream = new ByteArrayOutputStream();
            //response.setHeader("Content-Disposition","attchment;filename="+ URLEncoder.encode("TEST.png","utf-8"));
            //OutputStream outputStream=response.getOutputStream();

            byte[] buffer = new byte[1024];
            int bytesRead;
            while ((bytesRead = inputStream.read(buffer)) != -1) {
                //System.out.write(buffer,0,bytesRead);
                outputStream.write(buffer, 0, bytesRead);
                //response.getOutputStream().write(bytesRead);
            }

            //response.getOutputStream().close();
            byte[] bytes = outputStream.toByteArray();
            if (bytes.length > 0) {
                response.reset();
                response.setContentType("image/jpeg");
                response.getOutputStream().write(bytes);
                response.getOutputStream().flush();
                //return;
            }
            //response.getWriter(bytes);
            //outputStream.write(System.out);
            //outputStream.flush();
//            inputStream.close();
//            outputStream.close();
        } catch (NoSuchAlgorithmException e) {
            e.printStackTrace();
        } catch (KeyManagementException e) {
            e.printStackTrace();
        } finally {
            // Close resources
            if (inputStream != null) {
                try {
                    inputStream.close();
                } catch (IOException e) {
                    // Log error if needed
                }
            }
            if (outputStream != null) {
                try {
                    outputStream.close();
                } catch (IOException e) {
                    // Log error if needed
                }
            }
        }

方法三：

            // Web request setup
            HttpURLConnection connection = null;
            InputStream inputStream = null;
            ByteArrayOutputStream outputStream = null;

            try {

                // 禁用SSL证书验证
                TrustManager[] trustAllCerts = new TrustManager[]{new X509TrustManager() {
                    @Override
                    public java.security.cert.X509Certificate[] getAcceptedIssuers() {
                        return null;
                    }

                    @Override
                    public void checkClientTrusted(java.security.cert.X509Certificate[] certs, String authType) {
                    }

                    @Override
                    public void checkServerTrusted(java.security.cert.X509Certificate[] certs, String authType) {
                    }
                }};

// 创建SSLContext，使用禁用SSL证书验证的TrustManager
                SSLContext sslContext = SSLContext.getInstance("SSL");
                sslContext.init(null, trustAllCerts, new java.security.SecureRandom());

// 设置全局默认的SSLSocketFactory，使RestTemplate使用禁用SSL证书验证的SSLContext
                HttpsURLConnection.setDefaultSSLSocketFactory(sslContext.getSocketFactory());

                URL url = new URL(imageUrl);
                connection = (HttpURLConnection) url.openConnection();

                connection.setRequestMethod("GET");
                connection.setConnectTimeout(1000 * 60 * 3); // 3 minutes timeout
                connection.setReadTimeout(1000 * 60 * 3);
                connection.setInstanceFollowRedirects(false); // Disable auto redirect

                int responseCode = connection.getResponseCode();
                if (responseCode == HttpURLConnection.HTTP_OK) {
                    inputStream = connection.getInputStream();
                    outputStream = new ByteArrayOutputStream();

                    byte[] buffer = new byte[1024];
                    int bytesRead;
                    while ((bytesRead = inputStream.read(buffer)) != -1) {
                        outputStream.write(buffer, 0, bytesRead);
                    }

                    byte[] imageBytes = outputStream.toByteArray();
                    if (imageBytes.length > 0) {
                        response.reset();
                        response.setContentType("image/jpeg");
                        response.getOutputStream().write(imageBytes);
                        response.getOutputStream().flush();
                        return;
                    }
                }
            } catch (NoSuchAlgorithmException e) {
                e.printStackTrace();
            } catch (KeyManagementException e) {
                e.printStackTrace();
            } finally {
                // Close resources
                if (inputStream != null) {
                    try {
                        inputStream.close();
                    } catch (IOException e) {
                        // Log error if needed
                    }
                }
                if (outputStream != null) {
                    try {
                        outputStream.close();
                    } catch (IOException e) {
                        // Log error if needed
                    }
                }
                if (connection != null) {
                    connection.disconnect();
                }
            }
        }
    }