如何克隆 InputStream? [英] How to clone an InputStream?

问题描述

我有一个 InputStream，我将它传递给一个方法来进行一些处理.我将在其他方法中使用相同的 InputStream，但是在第一次处理之后，InputStream 出现在方法内部.

I have a InputStream that I pass to a method to do some processing. I will use the same InputStream in other method, but after the first processing, the InputStream appears be closed inside the method.

我如何克隆 InputStream 以发送到关闭他的方法?还有其他解决方案吗?

How I can clone the InputStream to send to the method that closes him? There is another solution?

关闭 InputStream 的方法是来自 lib 的外部方法.我无法控制是否关闭.

the methods that closes the InputStream is an external method from a lib. I dont have control about closing or not.

private String getContent(HttpURLConnection con) {
    InputStream content = null;
    String charset = "";
    try {
        content = con.getInputStream();
        CloseShieldInputStream csContent = new CloseShieldInputStream(content);
        charset = getCharset(csContent);            
        return  IOUtils.toString(content,charset);
    } catch (Exception e) {
        System.out.println("Error downloading page: " + e);
        return null;
    }
}

private String getCharset(InputStream content) {
    try {
        Source parser = new Source(content);
        return parser.getEncoding();
    } catch (Exception e) {
        System.out.println("Error determining charset: " + e);
        return "UTF-8";
    }
}

推荐答案

如果您只想多次读取相同的信息，并且输入的数据小到可以放入内存，您可以从您的 InputStream 到 ByteArrayOutputStream.

If all you want to do is read the same information more than once, and the input data is small enough to fit into memory, you can copy the data from your InputStream to a ByteArrayOutputStream.

然后你可以获取相关的字节数组并打开尽可能多的克隆"字节数组.ByteArrayInputStream随你喜欢.

Then you can obtain the associated array of bytes and open as many "cloned" ByteArrayInputStreams as you like.

ByteArrayOutputStream baos = new ByteArrayOutputStream();

// Code simulating the copy
// You could alternatively use NIO
// And please, unlike me, do something about the Exceptions :D
byte[] buffer = new byte[1024];
int len;
while ((len = input.read(buffer)) > -1 ) {
    baos.write(buffer, 0, len);
}
baos.flush();
    
// Open new InputStreams using recorded bytes
// Can be repeated as many times as you wish
InputStream is1 = new ByteArrayInputStream(baos.toByteArray()); 
InputStream is2 = new ByteArrayInputStream(baos.toByteArray()); 

但是如果您确实需要保持原始流打开以接收新数据，那么您将需要跟踪对close() 的外部调用.您需要防止以某种方式调用 close().

But if you really need to keep the original stream open to receive new data, then you will need to track the external call to close(). You will need to prevent close() from being called somehow.

从 Java 9 开始，中间位可以替换为 InputStream.transferTo:

Since Java 9 the the middle bits can be replaced with InputStream.transferTo:

ByteArrayOutputStream baos = new ByteArrayOutputStream();
input.transferTo(baos);
InputStream firstClone = new ByteArrayInputStream(baos.toByteArray()); 
InputStream secondClone = new ByteArrayInputStream(baos.toByteArray()); 

这篇关于如何克隆 InputStream?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！