【Java基础】图片压缩

最近有个需求，需要把图片字节码用Base64 encode之后作为请求报文的一部分调用外部服务方，服务方对图片的大小有要求，不能超过500KB，另一方面，请求报文太大，会出现如下错误：413 请求体过大

先看下现在的图片：

如果是线上的图片，我也写了个获取图片字节码，查看图片大小的小程序

public class GetImgSize {

    public static void main(String[] args) {

        String posUrl = "http://file11info.ppdai.com/4e598e3bd163405d90d8f7b7783d494d.jpg";

        byte[] a = getBy(posUrl);

        System.out.println(a.length);
    }

    private static byte[] getBy(String posUrl){
        try {
            URL url = new URL(posUrl);

            ByteArrayOutputStream outputStream = new ByteArrayOutputStream();

            try(InputStream inputStream = url.openStream()){
                int len = 0;
                byte[] buffer = new byte[1024];
                while (-1 != (len = inputStream.read(buffer))){
                    outputStream.write(buffer, 0, len);
                }
            }
            return outputStream.toByteArray();
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }
}

压缩函数如下

public class GetImgSize {

    public static void main(String[] args) throws IOException {

        String posUrl = "http://file11info.ppdai.com/4e598e3bd163405d90d8f7b7783d494d.jpg";

        byte[] a = compress(posUrl);

        System.out.println(a.length);

        File output = new File("./duke-compressed-005.jpg");
        OutputStream out = null;
        try {
            out = new FileOutputStream(output);
            out.write(a);
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }finally {
            if(out != null){
                out.flush();
                out.close();
            }
        }
    }

private static byte[] compress(String posUrl) throws IOException {
    ByteArrayOutputStream bos = new ByteArrayOutputStream();
    ImageOutputStream ios = null;
    byte [] data = null;
    ImageWriter writer = null;
    try {
        URL url = new URL(posUrl);
        BufferedImage bufferedImage = ImageIO.read(url);

        writer = ImageIO.getImageWritersByFormatName("jpg").next();

        ios = ImageIO.createImageOutputStream(bos);

        writer.setOutput(ios);

        ImageWriteParam param = writer.getDefaultWriteParam();
        if (param.canWriteCompressed()){
            param.setCompressionMode(ImageWriteParam.MODE_EXPLICIT);
            param.setCompressionQuality(0.5f);
        }

        writer.write(null, new IIOImage(bufferedImage, null, null), param);

        data = bos.toByteArray();
        
        return data;
    } catch (Exception e) {
        e.printStackTrace();
    }finally {
        bos.close();

        if(ios != null){
            ios.close();
        }

        if(writer != null){
            writer.dispose();
        }
    }
    return null;
}

 }