Java常用IO流详解

Posted 2020-11-18 xianya

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一、流的分类：

按照数据流向的不同：输入流输出流
按照处理数据的单位的不同：字节流字符流（处理的文本文件）
按照角色的不同：节点流（直接作用于文件的）处理流

二、IO的体系

抽象基类节点流（文件流）缓冲流（处理流的一种）
InputStream FileInputStream BufferedInputStream
OutputStream FileOutputStream BufferedOutputStream
Reader FileReader BufferedReader
Writer FileWriter BufferedWriter

三、实例

基类InputStream、OutputStream 字节流既可以用来处理媒体数据也可以用来处理文本数据

1. FileInputStream和FileOutputStream

package com.yyx.test;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;

public class FileInputStreamOutputStreamDemo {
    public static void main(String[] args) {
        testFileInputStreamOne();
        System.out.println("=================");
        testFileInputStreamTwo();
        System.out.println("=================");
        testFileOutputStreamOne();
        System.out.println("=================");
        testInputStreamOutputStreamOne();
        System.out.println("=================");
        testInputStreamOutputStreamTwo();
    }

    /**
     * 读取文本文件
     */
    public static void testFileInputStreamOne() {
        String pathname = "F:" + File.separator + "source.txt";
        File file = new File(pathname);
        FileInputStream fis = null;
        try {
            fis = new FileInputStream(file);
            // 读取到的数据要写入的数组
            byte[] b = new byte[5];
            // 每次读入到byte中的字节的长度
            int len;
            while ((len = fis.read(b)) != -1) {
                String str = new String(b, 0, len);
                System.out.print(str);
            }
            System.out.println();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (fis != null) {
                try {
                    fis.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    /**
     * 读取文本文件
     */
    public static void testFileInputStreamTwo() {
        String pathname = "F:" + File.separator + "source.txt";
        File file = new File(pathname);
        FileInputStream fis = null;
        try {
            fis = new FileInputStream(file);
            int b;
            /*
             * read():读取文件的一个字节。当执行到文件结尾时，返回-1 此方法如文件内容有中文名出现乱码
             */
            while ((b = fis.read()) != -1) {
                System.out.print((char) b);
            }
            System.out.println();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (fis != null) {
                try {
                    fis.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    /**
     * 写入文本文件
     */
    public static void testFileOutputStreamOne() {
        String pathname = "F:" + File.separator + "target.txt";
        File file = new File(pathname);
        FileOutputStream fos = null;
        try {
            fos = new FileOutputStream(file);
            String str = "*中国--China*";
            fos.write(str.getBytes());
            System.out.println("写入成功");
            fos.flush();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (fos != null) {
                try {
                    fos.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    /**
     * 复制文本文件
     */
    public static void testInputStreamOutputStreamOne() {
        // 此处两个文件都已存在
        String sourcePathName = "F:" + File.separator + "source.txt";
        String targetPathName = "F:" + File.separator + "target.txt";
        File sourceFile = new File(sourcePathName);
        File targetFile = new File(targetPathName);
        FileInputStream fileInputStream = null;
        FileOutputStream fileOutputStream = null;
        try {
            fileInputStream = new FileInputStream(sourceFile);
            fileOutputStream = new FileOutputStream(targetFile);
            // 3.实现文件的复制
            byte[] b = new byte[1024];
            int len;
            while ((len = fileInputStream.read(b)) != -1) {
                fileOutputStream.write(b, 0, len);
            }
            fileOutputStream.flush();
            System.out.println("复制文本成功");
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (fileInputStream != null) {
                try {
                    fileInputStream.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (fileOutputStream != null) {
                try {
                    fileOutputStream.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    /**
     * 复制图片文件
     */
    public static void testInputStreamOutputStreamTwo() {
        // 此处两个文件都已存在
        String sourcePathName = "F:" + File.separator + "source.jpg";
        String targetPathName = "F:" + File.separator + "target.jpg";
        File sourceFile = new File(sourcePathName);
        File targetFile = new File(targetPathName);
        FileInputStream fileInputStream = null;
        FileOutputStream fileOutputStream = null;
        try {
            fileInputStream = new FileInputStream(sourceFile);
            fileOutputStream = new FileOutputStream(targetFile);
            // 3.实现文件的复制
            byte[] b = new byte[1024];
            int len;
            while ((len = fileInputStream.read(b)) != -1) {
                fileOutputStream.write(b, 0, len);
            }
            System.out.println("复制图片成功");
            fileOutputStream.flush();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (fileInputStream != null) {
                try {
                    fileInputStream.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (fileOutputStream != null) {
                try {
                    fileOutputStream.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

2. BufferedInputStream和BufferedOutputStream

package com.yyx.test;

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;

public class FileInputStreamOutputStreamDemo {
    public static void main(String[] args) {
        // 此处两个文件都已存在
        String sourcePathName = "F:" + File.separator + "source.jpg";
        String targetPathName = "F:" + File.separator + "target.jpg";
        File sourceFile = new File(sourcePathName);
        File targetFile = new File(targetPathName);
        FileInputStream fileInputStream = null;
        FileOutputStream fileOutputStream = null;
        BufferedInputStream bufferedInputStream = null;
        BufferedOutputStream bufferedOutputStream = null;
        try {
            fileInputStream = new FileInputStream(sourceFile);
            fileOutputStream = new FileOutputStream(targetFile);
            bufferedInputStream = new BufferedInputStream(fileInputStream);
            bufferedOutputStream = new BufferedOutputStream(fileOutputStream);
            // 3.实现文件的复制
            byte[] b = new byte[1024];
            int len;
            while ((len = bufferedInputStream.read(b)) != -1) {
                bufferedOutputStream.write(b, 0, len);
            }
            System.out.println("复制图片成功");
            bufferedOutputStream.flush();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (bufferedInputStream != null) {
                try {
                    bufferedInputStream.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (bufferedOutputStream != null) {
                try {
                    bufferedOutputStream.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

基类Reader、Writer 字符流只用来处理文本数据

1. FileReader和FileWriter

package com.yyx.test;

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

public class FileReaderWriterDemo {
    public static void main(String[] args) {
        testReaderOne();
        System.out.println("=================");
        testReaderTwo();
        System.out.println("=================");
        testWriter();
        System.out.println("=================");
        testReaderWriter();
    }

    /**
     * 推荐:使用字节组读取
     */
    public static void testReaderOne() {
        // 方法中文件已经存在
        String pathname = "F:" + File.separator + "source.txt";
        File file = new File(pathname);
        FileReader fr = null;
        try {
            fr = new FileReader(file);
            char[] buf = new char[6];
            int num = 0;
            while ((num = fr.read(buf)) != -1) {
                String str = new String(buf, 0, num);
                System.out.print(str);
            }
            System.out.println();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    /**
     * 使用单个字母读取
     */
    public static void testReaderTwo() {
        // 方法中文件已经存在
        String pathname = "F:" + File.separator + "source.txt";
        File file = new File(pathname);
        FileReader fr = null;
        try {
            fr = new FileReader(file);
            int ch;
            while ((ch = fr.read()) != -1) {
                System.out.print((char) ch);
            }
            System.out.println();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public static void testWriter() {
        String pathname = "F:" + File.separator + "target.txt";
        File file = new File(pathname);
        FileWriter fw = null;
        try {
            fw = new FileWriter(file);
            String str = "*中国--China*";
            fw.write(str);
            System.out.println("写入成功");
            /*
             * flush和close的区别：flush刷新后可以继续输入，close刷新后不能继续输入
             */
            fw.flush();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (fw != null) {
                try {
                    fw.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    /**
     * 复制文件
     */
    public static void testReaderWriter() {
        // 此处两个文件都已存在
        String sourcePathName = "F:" + File.separator + "source.txt";
        String targetPathName = "F:" + File.separator + "target.txt";
        File sourceFile=new File(sourcePathName);
        File targetFile=new File(targetPathName);
        FileReader fileReader = null;
        FileWriter fileWriter = null;
        try {
            fileReader = new FileReader(sourceFile);
            // true表示追加写入，默认是false
            fileWriter = new FileWriter(targetFile, true);
            char[] buf = new char[1024];
            // 将文件读取到buf数组中
            int num = 0;
            while ((num = fileReader.read(buf)) != -1) {
                fileWriter.write(new String(buf, 0, num));
            }
            System.out.println("复制成功");
            fileWriter.flush();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (fileReader != null) {
                try {
                    fileReader.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (fileWriter != null) {
                try {
                    fileWriter.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

2. BufferedReader和BufferedWriter

BufferedWriter:将文本写入字符输出流，缓冲各个字符，从而提供单个字符、数组和字符串的高效写入
BufferedReader:从字符输入流中读取文本，缓冲各个字符，从而实现字符、数组和行的高效读取

package com.yyx.test;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;

public class FileReaderWriterDemo {
    public static void main(String[] args) {
        // 此处两个文件都已存在
        String sourcePathName = "F:" + File.separator + "source.txt";
        String targetPathName = "F:" + File.separator + "target.txt";
        File sourceFile=new File(sourcePathName);
        File targetFile=new File(targetPathName);
        FileReader fileReader = null;
        FileWriter fileWriter = null;
        BufferedReader bufferedReader = null;
        BufferedWriter bufferedWriter = null;
        try {
            fileReader = new FileReader(sourceFile);
            // true表示追加写入，默认是false
            fileWriter = new FileWriter(targetFile, true);
            bufferedReader = new BufferedReader(fileReader);
            bufferedWriter = new BufferedWriter(fileWriter);
            char[] buf = new char[1024];
            // 将文件读取到buf数组中
            int num = 0;
            while ((num = bufferedReader.read(buf)) != -1) {
                bufferedWriter.write(new String(buf, 0, num));
            }
            System.out.println("复制成功");
            bufferedWriter.flush();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (bufferedReader != null) {
                try {
                    bufferedReader.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (bufferedWriter != null) {
                try {
                    bufferedWriter.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

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