Java 字符流

Java 中的字符流也称为字符输入/输出流，是把字符数据读入程序或者将字符数据写出程序的流。字符流以字符为单位读取数据，而不是以字节为单位，因此可以更有效地处理文本文件。字符流基于字符集，因此可以以更高效的编码方式来处理文本，从而提高性能。 Java 中提供了两个基本的字符流类：Reader 和 Writer，它们分别用于读取和写入数据。比如，FileReader 用于从文件中读取数据，而 FileWriter 用于将数据写入文件中。

常见的字符流方法：

• InputStreamReader / OutputStreamWriter
• BufferedReader / BufferedWriter
• CharArrayReader / CharArrayWriter
• StringReader / StringWriter
• FileReader / FileWriter

InputStreamReader / OutputStreamWriter

示例：

import java.io.*;

public class StreamReaderWriterDemo {
    public static void main(String[] args) {
        try (
            InputStreamReader isr = new InputStreamReader(System.in);
            OutputStreamWriter osw = new OutputStreamWriter(System.out);
        ) {
            osw.write("Please input something: \n");
            osw.flush();
            char[] buffer = new char[20];
            isr.read(buffer);
            osw.write(("Your input is:"));
            osw.write(buffer); // 乱码
            osw.write("\n");
            osw.flush();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

BufferedReader / BufferedWriter

示例：

import java.io.*;

public class BufferedReaderWriterDemo {

    public static void main(String[] args) {
        try (BufferedReader br = new BufferedReader(new FileReader("input.txt"))) {
            String line;
            while ((line = br.readLine()) != null) {
                System.out.println(line);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }

        try (BufferedWriter bw = new BufferedWriter(new FileWriter("output.txt"))) {
            bw.write("Hello World!");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

CharArrayReader / CharArrayWriter

示例：

import java.io.CharArrayReader;
import java.io.CharArrayWriter;
import java.io.IOException;

public class CharArrayReaderWriterDemo {

    public static void main(String[] args) {
        char[] charArray = {'H', 'e', 'l', 'l', 'o'};
        char[] newCharArray = new char[charArray.length];

        try (CharArrayReader reader = new CharArrayReader(charArray);
             CharArrayWriter writer = new CharArrayWriter())
        {
            int c;
            while ((c = reader.read()) != -1) {
                writer.write(c);
            }
            newCharArray = writer.toCharArray();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

StringReader / StringWriter

示例：

import java.io.IOException;
import java.io.StringReader;
import java.io.StringWriter;

public class StringReaderWriterDemo {

    public static void main(String[] args) {
        String str = "Hello World!";
        StringBuilder builder = new StringBuilder();

        try (StringReader reader = new StringReader(str);
             StringWriter writer = new StringWriter()) {
            int c;
            while ((c = reader.read()) != -1) {
                writer.write(c);
            }
            builder.append(writer);
            System.out.println(builder);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

FileReader / FileWriter

示例：

import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;

public class FileReaderWriterDemo {

    public static void main(String[] args) {
        try (FileReader reader = new FileReader("src.txt");
             FileWriter writer = new FileWriter("dest.txt"))
        {
            int c;
            while ((c = reader.read()) != -1) {
                writer.write(c);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

如何检测字符流的结束标志？—— 字符流的结束标志通常是 -1，当读取到 -1 时，表示字符流已经读取完毕。例如，InputStreamReader 类的 read() 方法返回的是 int 类型，当成功读取一个字符时，返回的是字符的 ASCII 值，而当读取到文件末尾时，返回 -1。

if (inputStreamReader.read() == -1) {
    //字符流已结束
}