如果您有java.io.InputStream对象,应该如何处理该对象并生成String?


假设我有一个包含文本数据的InputStream,我想将其转换为String,例如,我可以将其写入日志文件。

获取InputStream并将其转换为字符串的最简单方法是什么?

public String convertStreamToString(InputStream is) {
// ???
}

当前回答

下面的代码对我有用。

URL url = MyClass.class.getResource("/" + configFileName);
BufferedInputStream bi = (BufferedInputStream) url.getContent();
byte[] buffer = new byte[bi.available() ];
int bytesRead = bi.read(buffer);
String out = new String(buffer);

请注意,根据Java文档,available()方法可能不适用于InputStream,但始终适用于BufferedInputStream。如果您不想使用available()方法,我们可以始终使用以下代码

URL url = MyClass.class.getResource("/" + configFileName);
BufferedInputStream bi = (BufferedInputStream) url.getContent();
File f = new File(url.getPath());
byte[] buffer = new byte[ (int) f.length()];
int bytesRead = bi.read(buffer);
String out = new String(buffer);

我不确定是否会有任何编码问题。如果代码有任何问题,请发表评论。

其他回答

使用java 9中支持的java.io.InputStream.transferTo(OutputStream)和ByteArrayOutputStream.toString(String),该字符串采用字符集名称:

public static String gobble(InputStream in, String charsetName) throws IOException {
    ByteArrayOutputStream bos = new ByteArrayOutputStream();
    in.transferTo(bos);
    return bos.toString(charsetName);
}

如果使用流读取器,请确保在结束时关闭流

private String readStream(InputStream iStream) throws IOException {
    //build a Stream Reader, it can read char by char
    InputStreamReader iStreamReader = new InputStreamReader(iStream);
    //build a buffered Reader, so that i can read whole line at once
    BufferedReader bReader = new BufferedReader(iStreamReader);
    String line = null;
    StringBuilder builder = new StringBuilder();
    while((line = bReader.readLine()) != null) {  //Read till end
        builder.append(line);
        builder.append("\n"); // append new line to preserve lines
    }
    bReader.close();         //close all opened stuff
    iStreamReader.close();
    //iStream.close(); //EDIT: Let the creator of the stream close it!
                       // some readers may auto close the inner stream
    return builder.toString();
}

编辑:在JDK7+上,可以使用trywithresources构造。

/**
 * Reads the stream into a string
 * @param iStream the input stream
 * @return the string read from the stream
 * @throws IOException when an IO error occurs
 */
private String readStream(InputStream iStream) throws IOException {

    //Buffered reader allows us to read line by line
    try (BufferedReader bReader =
                 new BufferedReader(new InputStreamReader(iStream))){
        StringBuilder builder = new StringBuilder();
        String line;
        while((line = bReader.readLine()) != null) {  //Read till end
            builder.append(line);
            builder.append("\n"); // append new line to preserve lines
        }
        return builder.toString();
    }
}

这个问题的解决方案不是最简单的,但由于没有提到NIO流和通道,这里有一个使用NIO通道和ByteBuffer将流转换为字符串的版本。

public static String streamToStringChannel(InputStream in, String encoding, int bufSize) throws IOException {
    ReadableByteChannel channel = Channels.newChannel(in);
    ByteBuffer byteBuffer = ByteBuffer.allocate(bufSize);
    ByteArrayOutputStream bout = new ByteArrayOutputStream();
    WritableByteChannel outChannel = Channels.newChannel(bout);
    while (channel.read(byteBuffer) > 0 || byteBuffer.position() > 0) {
        byteBuffer.flip();  //make buffer ready for write
        outChannel.write(byteBuffer);
        byteBuffer.compact(); //make buffer ready for reading
    }
    channel.close();
    outChannel.close();
    return bout.toString(encoding);
}

下面是如何使用它的示例:

try (InputStream in = new FileInputStream("/tmp/large_file.xml")) {
    String x = streamToStringChannel(in, "UTF-8", 1);
    System.out.println(x);
}

对于大型文件,此方法的性能应该很好。

String inputStreamToString(InputStream inputStream, Charset charset) throws IOException {
    try (
            final StringWriter writer = new StringWriter();
            final InputStreamReader reader = new InputStreamReader(inputStream, charset)
        ) {
        reader.transferTo(writer);
        return writer.toString();
    }
}

纯Java标准库解决方案-无库自Java 10以来-Reader#transferTo(Java.io.Writer)无环溶液无新行字符处理

这里有一种仅使用标准Java库的方法(请注意,流没有关闭,您的里程可能会有所不同)。

static String convertStreamToString(java.io.InputStream is) {
    java.util.Scanner s = new java.util.Scanner(is).useDelimiter("\\A");
    return s.hasNext() ? s.next() : "";
}

我从“愚蠢的扫描仪技巧”一文中学会了这个技巧。它工作的原因是因为Scanner迭代流中的令牌,在这种情况下,我们使用“输入边界的开始”(\A)来分离令牌,从而为流的整个内容只提供一个令牌。

注意,如果您需要明确输入流的编码,可以向Scanner构造函数提供第二个参数,指示要使用的字符集(例如“UTF-8”)。

雅各布也收到了帽子提示,他曾向我指出了上述文章。