在JDK7、8版本中用 ImageIO.write进行图片输出时，如果输出PNG格式图片非常的缓慢 

Poor performances of imwrite, especially for png extension.

上代码-解决前：

@Test
public void testWirte() throws Exception {
        String dir = "/Users/user/Downloads/testimg/";
        final MockMultipartFile file = new MockMultipartFile("big5.png", new FileInputStream(new File(dir + "big5.png")));
        final BufferedImage bufferedImage = ImageIO.read(file.getInputStream());
        long start = System.currentTimeMillis();
        ImageIO.write(bufferedImage,"png",new FileOutputStream(new File(dir + "/out/big5-out.png")));
        System.out.println((System.currentTimeMillis() - start) +  " ms ");
}

5198 ms  

 解决后：

@Test
public void testWirte1() throws Exception {
        String dir = "/Users/user/Downloads/testimg/";
        final MockMultipartFile file = new MockMultipartFile("big5.png", new FileInputStream(new File(dir + "big5.png")));
        final BufferedImage bufferedImage = ImageIO.read(file.getInputStream());
        long start = System.currentTimeMillis();
        ImageWriter writer = ImageIO.getImageWritersByFormatName("png").next();
        ImageWriteParam writeParam = writer.getDefaultWriteParam();
        writeParam.setCompressionMode(ImageWriteParam.MODE_EXPLICIT);
        writeParam.setCompressionQuality(0.9f);
        final FileImageOutputStream stream = new FileImageOutputStream(new File(dir + "/out/big5-out.png"));
        try {
            writer.setOutput(stream);
            writer.write(null, new IIOImage(bufferedImage, null, null), writeParam);
        } finally {
            stream.close();
            writer.dispose();
        }
        System.out.println((System.currentTimeMillis() - start) + " ms ");
}

2127 ms 

测试图片说明：5.7M png格式

问题说明：

这是一个JDK7、8ImageIO的一个BUG，在9进行了修复，详情参加

[JDK-6488522] PNG writer should permit setting compression level and iDAT chunk maximum size - Java Bug Systemhttps://bugs.openjdk.java.net/browse/JDK-6488522解决步骤：

1.下载jdk9-png-writer-backport源码

https://github.com/gredler/jdk9-png-writer-backporthttps://github.com/gredler/jdk9-png-writer-backport2.把对应内容打包到私仓或者直接copy至项目目录

其他方案：

pngencoderhttps://hub.xn--gzu630h.xn--kpry57d/pngencoder/pngencoder 

这个目前还在测试中，速度优于上面的方案 

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