工作中遇到通过图片的url获取图片base64位的需求。一开始是用网上的方法，通过工具类Toolkit，虽然实现的代码比较简短，不过偶尔会遇到图片转成base64位不正确的情况，至今不知道为啥。

之后，又去网上搜了通过获取图片的二进制流转换成base64的方式，两种方式，都是亲测有效，通过Toolkit偶尔会出现，转base64后，展示不完整的问题。所以建议用通过下载二进制流转换的方式进行转换。

下面附上代码：

import java.awt.image.BufferedImage;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;

import javax.imageio.ImageIO;
import javax.swing.ImageIcon;


import java.awt.Graphics;
import java.awt.GraphicsConfiguration;
import java.awt.GraphicsDevice;
import java.awt.GraphicsEnvironment;
import java.awt.HeadlessException;
import java.awt.Image;
import java.awt.Toolkit;
import java.awt.Transparency;
import java.net.HttpURLConnection;
import java.net.URL;


public class ImageUtils {

    
    
    public static String getBase64ByImgUrl(String url){
        String suffix = url.substring(url.lastIndexOf(".") + 1);
        try {
            URL urls = new URL(url);
            ByteArrayOutputStream  baos = new ByteArrayOutputStream();
            Image image = Toolkit.getDefaultToolkit().getImage(urls);
            BufferedImage  biOut = toBufferedImage(image);
            ImageIO.write(biOut, suffix, baos);
            String base64Str = Base64Util.encode(baos.toByteArray());
            return base64Str;
        } catch (Exception e) {
            return "";
        }
        
    }
    
    public static BufferedImage toBufferedImage(Image image) {  
        if (image instanceof BufferedImage) {  
            return (BufferedImage) image;  
        }  
        // This code ensures that all the pixels in the image are loaded  
        image = new ImageIcon(image).getImage();  
        BufferedImage bimage = null;  
        GraphicsEnvironment ge = GraphicsEnvironment  
                .getLocalGraphicsEnvironment();  
        try {  
            int transparency = Transparency.OPAQUE;  
            GraphicsDevice gs = ge.getDefaultScreenDevice();  
            GraphicsConfiguration gc = gs.getDefaultConfiguration();  
            bimage = gc.createCompatibleImage(image.getWidth(null),  
                    image.getHeight(null), transparency);  
        } catch (HeadlessException e) {  
            // The system does not have a screen  
        }  
        if (bimage == null) {  
            // Create a buffered image using the default color model  
            int type = BufferedImage.TYPE_INT_RGB;  
            bimage = new BufferedImage(image.getWidth(null),  
                    image.getHeight(null), type);  
        }  
        // Copy image to buffered image  
        Graphics g = bimage.createGraphics();  
        // Paint the image onto the buffered image  
        g.drawImage(image, 0, 0, null);  
        g.dispose();  
        return bimage;  
    }  
    /**
     * 通过图片的url获取图片的base64字符串
     * @param imgUrl    图片url
     * @return    返回图片base64的字符串
     */
    public static String image2Base64(String imgUrl) {  

        URL url = null;  

        InputStream is = null;   

        ByteArrayOutputStream outStream = null;  

        HttpURLConnection httpUrl = null;  

        try{  

            url = new URL(imgUrl);  

            httpUrl = (HttpURLConnection) url.openConnection();  

            httpUrl.connect();  

            httpUrl.getInputStream();  

            is = httpUrl.getInputStream();            

              

            outStream = new ByteArrayOutputStream();  

            //创建一个Buffer字符串  

            byte[] buffer = new byte[1024];  

            //每次读取的字符串长度，如果为-1，代表全部读取完毕  

            int len = 0;  

            //使用一个输入流从buffer里把数据读取出来  

            while( (len=is.read(buffer)) != -1 ){  

                //用输出流往buffer里写入数据，中间参数代表从哪个位置开始读，len代表读取的长度  

                outStream.write(buffer, 0, len);  

            }  

            // 对字节数组Base64编码  

            return Base64Util.encode(outStream.toByteArray());  

        }catch (Exception e) {  

            e.printStackTrace();  

        }  

        finally{  

            if(is != null)  

            {  

                try {  

                    is.close();  

                } catch (IOException e) {  

                    e.printStackTrace();  

                }  

            }  

            if(outStream != null)  

            {  

                try {  

                    outStream.close();  

                } catch (IOException e) {  

                    e.printStackTrace();  

                }  

            }  

            if(httpUrl != null)  

            {  

                httpUrl.disconnect();  

            }  

        }  

        return imgUrl;  

    }  
}

其中

getBase64ByImgUrl方法为通过Toolkit获取的方式，至于为啥没注释，因为我也看不懂原理，也是抄来的。

image2Base64方法为通过下载二进制流的方式，当然也是抄来的。写出来是为了总结一下。下次遇到相同的问题，不用到处查了。
附上Base64Util的代码：

import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.IOException;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import javax.imageio.stream.FileImageInputStream;

import sun.misc.BASE64Decoder;
import sun.misc.BASE64Encoder;

public class Base64Util{
    /**
     * 字符串转图片
     * @param base64Str
     * @return
     */
    public static byte[] decode(String base64Str){
        byte[] b = null;
        BASE64Decoder decoder = new BASE64Decoder();
        try {
            b = decoder.decodeBuffer(replaceEnter(base64Str));
        } catch (IOException e) {
            e.printStackTrace();
        }
        return b;
    }

    /**
     * 图片转字符串
     * @param image
     * @return
     */
    public static String encode(byte[] image){
        BASE64Encoder decoder = new BASE64Encoder();
        return replaceEnter(decoder.encode(image));
    }

    public static String encode(String uri){
        BASE64Encoder encoder = new BASE64Encoder();
        return replaceEnter(encoder.encode(uri.getBytes()));
    }

    /**
     *
     * @path    图片路径
     * @return
     */

    public static byte[] imageTobyte(String path){
        byte[] data = null;
        FileImageInputStream input = null;
        try {
            input = new FileImageInputStream(new File(path));
            ByteArrayOutputStream output = new ByteArrayOutputStream();
            byte[] buf = new byte[1024];
            int numBytesRead = 0;
            while((numBytesRead = input.read(buf)) != -1){
                output.write(buf, 0, numBytesRead);
            }
            data = output.toByteArray();
            output.close();
            input.close();

        } catch (Exception e) {
            e.printStackTrace();
        }

        return data;
    }



    public static String replaceEnter(String str){
        String reg ="[\n-\r]";
        Pattern p = Pattern.compile(reg);
        Matcher m = p.matcher(str);
        return m.replaceAll("");
    }


}

转载：https://www.cnblogs.com/duck-ifox/p/9084049.html