003-Spring 中的StreamUtils

一、概述

　　StreamUtils是spring中用于处理流的类，是java.io包中inputStream和outputStream，不是java8中Steam。使用时仅依赖spring-core

二、使用

基本的输入流读取成字符串

    public static String getStringFromInputStream(InputStream input) throws IOException {
        StringWriter writer = new StringWriter();
        IOUtils.copy(input, writer, "UTF-8");
        return writer.toString();
    }

2.1、拷贝inputStream内容至outputStream：StreamUtils.copy(in, out);

两个参数，第一个为输入，第二个为拷贝至的

    @Test
    public void whenCopyInputStreamToOutputStream_thenCorrect() throws IOException {
        String inputFileName = "src/test/resources/input.txt";
        String outputFileName = "src/test/resources/output.txt";
        File outputFile = new File(outputFileName);
        InputStream in = new FileInputStream(inputFileName);
        OutputStream out = new FileOutputStream(outputFile);

        StreamUtils.copy(in, out);

        assertTrue(outputFile.exists());
        String inputFileContent = getStringFromInputStream(new FileInputStream(inputFileName));
        String outputFileContent = getStringFromInputStream(new FileInputStream(outputFileName));
        assertEquals(inputFileContent, outputFileContent);
    }

2.2、拷贝inputStream部分内容至outputStream，使用copyRange()方法拷贝一定范围的内容：

copyRange方法有四个参数，inputStream，outputStream，开始拷贝位置，结束拷贝位置。如果我们指定的长度超过inputStream的长度呢？copyRange方法仅拷贝至流的结尾。

    @Test
    public void whenCopyRangeOfInputStreamToOutputStream_thenCorrect() throws IOException {
        String inputFileName = "src/test/resources/input.txt";
        String outputFileName = "src/test/resources/output.txt";
        File outputFile = new File(outputFileName);
        InputStream in = new FileInputStream(inputFileName);
        OutputStream out = new FileOutputStream(outputFileName);

        StreamUtils.copyRange(in, out, 1, 10);

        assertTrue(outputFile.exists());
        String inputFileContent = getStringFromInputStream(new FileInputStream(inputFileName));
        String outputFileContent = getStringFromInputStream(new FileInputStream(outputFileName));

        assertEquals(inputFileContent.substring(1, 11), outputFileContent);
    }

2.3、拷贝字符串至outputStream

copy方法带三个参数：被拷贝的字符串，写文件时指定的字符集，指定目的地（outputStream）

    @Test
    public void whenCopyStringToOutputStream_thenCorrect() throws IOException {
        String string = "Should be copied to OutputStream.";
        String outputFileName = "src/test/resources/output2.txt";
        File outputFile = new File(outputFileName);
        OutputStream out = new FileOutputStream(outputFileName);

        StreamUtils.copy(string, StandardCharsets.UTF_8, out);

        assertTrue(outputFile.exists());
        String outputFileContent = getStringFromInputStream(new FileInputStream(outputFileName));
        assertEquals(outputFileContent, string);
    }

2.4、将inputStream内容拷贝为字符串

    @Test
    public void whenCopyInputStreamToString_thenCorrect() throws IOException {
        String inputFileName = "src/test/resources/input.txt";
        InputStream is = new FileInputStream(inputFileName);
        String content = StreamUtils.copyToString(is, StandardCharsets.UTF_8);

        String inputFileContent = getStringFromInputStream(new FileInputStream(inputFileName));
        System.out.println(content);
        assertEquals(inputFileContent, content);
    }

2.5、拷贝inputStream内容至字节数组

    @Test
    public void whenCopyInputStreamToByteArray_thenCorrect() throws IOException {
        String inputFileName = "src/test/resources/input.txt";
        InputStream is = new FileInputStream(inputFileName);
        byte[] out = StreamUtils.copyToByteArray(is);

        String content = new String(out);
        String inputFileContent = getStringFromInputStream(new FileInputStream(inputFileName));

        assertEquals(inputFileContent, content);
    }

2.6、删除流中所有剩余数据

StreamUtils.drain(in);

2.7、获得一个有效空输入流

public InputStream getInputStream() {
    return StreamUtils.emptyInput();
}

2.8、两个重载方法nonClosing(),inputStream和outputStream流可以作为参数，用于返回无需关闭的inputStream和outputStream流

public InputStream getNonClosingInputStream() throws IOException {
    InputStream in = new FileInputStream("src/test/resources/input.txt");
    return StreamUtils.nonClosing(in);
}