今天，我们将学习如何在Java中将InputStream转换为String。
在处理文件时，有时我们必须读取文件，然后将InputStream数据转换为String进行进一步处理。

Java InputStream转换为String

我们可以通过多种方式将InputStream转换为String。

• BufferedReader
• StringWriter
• Scanner

让我们研究一下所有这些类，以将InputStream对象转换为String。

1. BufferedReader

这是一个简单的程序，显示了使用BufferedReader的java InputStream到String的转换。

import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStreamReader;

public class InputStreamToStringUsingBufferedReader {

	final static String fileName = "/Users/hyman/Downloads/file.txt";

	public static void main(String[] args) throws IOException {
		long start = System.currentTimeMillis();
		FileInputStream fileInputStream = null;
		BufferedReader bufferedReader = null;
		StringBuilder inputSB = null;
		try {
			fileInputStream = new FileInputStream(fileName);
			bufferedReader = new BufferedReader(new InputStreamReader(fileInputStream, "UTF-8"));
			inputSB = new StringBuilder();
			String line = bufferedReader.readLine();
			while (line != null) {
				inputSB.append(line);
				line = bufferedReader.readLine();
				if (line != null) {
					//add new line character
					inputSB.append("\n");
				}
			}
		} finally {
			bufferedReader.close();
			fileInputStream.close();
		}
		String str = inputSB.toString();
		long end = System.currentTimeMillis();
		System.out.println("InputStream to String using BufferedReader = " + (end - start) + "ms");
	}

}

2. StringWriter

我们也可以使用StringWriter将InputStream转换为String。
请注意，它也使用了" BufferedReader"，但是将数据写入StringWriter，然后轻松转换为String。

import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.Reader;
import java.io.StringWriter;
import java.io.Writer;

public class InputStreamToStringUsingStringWriter {

	final static String fileName = "/Users/hyman/Downloads/file.txt";

	public static void main(String args[]) throws IOException {
		long start = System.currentTimeMillis();
		FileInputStream fileInputStream = null;
		Reader reader = null;
		Writer writer = new StringWriter();
		char[] buffer = new char[1024];
		try {
			fileInputStream = new FileInputStream(fileName);
			reader = new BufferedReader(new InputStreamReader(fileInputStream, "UTF-8"));
			int n;
			while ((n = reader.read(buffer)) != -1) {
				writer.write(buffer, 0, n);
			}
		} finally {
			reader.close();
			writer.close();
			fileInputStream.close();
		}
		String str = writer.toString();
		long end = System.currentTimeMillis();
		System.out.println("InputStream to String using StringWriter = " + (end - start) + "ms");
	}
}

3.扫描仪

我们还可以使用Scanner类将文件读取为InputStream并转换为String。

import java.io.FileInputStream;
import java.io.IOException;
import java.util.Scanner;

public class InputStreamToStringUsingScanner {

	final static String fileName = "/Users/hyman/Downloads/file.txt";

	public static void main(String[] args) throws IOException {
		long start = System.currentTimeMillis();
		FileInputStream fileInputStream = null;
		Scanner scanner = null;
		try {
			fileInputStream = new FileInputStream(fileName);
			scanner = new Scanner(fileInputStream, "UTF-8");
			String str = scanner.useDelimiter("\A").next();
		} finally {
			fileInputStream.close();
			scanner.close();
		}
		long end = System.currentTimeMillis();
		System.out.println("InputStream to String using Scanner = "+(end-start)+"ms");
	}

}