java文件读写

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java文件读写涉及到很多IO操作，读写方法较多，下面从字节流、字符流、节点流、处理流等方面进行介绍。

1.基本概念

输出流：程序->文件
输入流：文件->程序
字节流：一次读入或者读出是8位二进制
字符流：一次读入或者读出是16位二进制流
节点流：直接与数据源相连。
处理流：在节点流上再套接一层，对一个已知流的连接和封装，构造方法带一个其他流对象作参数，通过所封装的流的功能调用实现数据读写。一个流对象经过其他流的多次包装，称为流的连接。

2.基本关系

这里写图片描述
红色标记的为与文件读写有关的类，带Buffered前缀的是处理流，会设置一个缓冲区，减少读写磁盘的次数。左边代表字符流，右边代表字节流。

3.例子

import java.io.*;public class Exam1 {    public static void main(String[] args) throws IOException {        String filename ="file"+File.separator+"test1.txt";        String outputfile ="file"+File.separator+"output.txt";        fileInpputStream(filename);        fileOutputStream();        bufferedInputStream(filename);        bufferedOutputStream(filename,outputfile);        readFileByChars(filename);        writeByFileReader(outputfile);        readByBufferedReader(filename);        writeByBufferedReader(outputfile);    }    /**     * 字节流：FileInputStream  FileOutputStream     */    public  static void fileInpputStream(String fileName) {        // 一般先创建file对象        FileInputStream fileInput = null;        try {            File file = new File(fileName);            if (!file.exists()) {                file.createNewFile();            }            byte[] buffer = new byte[1024];            fileInput = new FileInputStream(file);            int byteread = 0;            // byteread表示一次读取到buffers中的数量。            while ((byteread = fileInput.read(buffer)) != -1) {                System.out.write(buffer, 0, byteread);            }        } catch (Exception e) {            // TODO: handle exception        } finally {            try {                if (fileInput != null) {                    fileInput.close();                }            } catch (IOException e) {                // TODO Auto-generated catch block                e.printStackTrace();            }        }    }    public static void fileOutputStream() {        FileOutputStream fop = null;        File file;        String content = "fileOutputStream";        try {            file = new File("file"+File.separator+"test1.txt");            fop = new FileOutputStream(file,true);            if (!file.exists()) {                file.createNewFile();            }            byte[] contentInBytes = content.getBytes();            fop.write(contentInBytes);            fop.flush();            fop.close();        } catch (IOException e) {            e.printStackTrace();        } finally {            try {                if (fop != null) {                    fop.close();                }            } catch (IOException e) {                e.printStackTrace();            }        }    }    /**     * 缓冲字节流：BufferedInputStream     * @throws IOException     */    public static void bufferedInputStream(String filename)throws IOException {        File file = new File(filename);        FileInputStream fis = new FileInputStream(file);        BufferedInputStream bis = new BufferedInputStream(fis);        byte[] contents = new byte[1024];        int byteRead = 0;        String strFileContents;        try {            while((byteRead = bis.read(contents)) != -1){                strFileContents = new String(contents,0,byteRead);                System.out.println(strFileContents);            }        } catch (IOException e) {            // TODO Auto-generated catch block            e.printStackTrace();        }        bis.close();    }    /**     * 缓冲字节流：BufferedOutputStream     * @throws IOException     */    public  static void bufferedOutputStream(String filename,String outputfile) throws IOException {        BufferedInputStream bis = new BufferedInputStream(new FileInputStream(filename));        BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream(outputfile));        int i;        do {            i = bis.read();            if (i != -1) {                bos.write(i);            }        } while (i != -1);        bis.close();        bos.close();    }    /**     * 字符流:FileReader     */    public static void readFileByChars(String fileName) {        FileReader reader = null;        System.out.print("FileReader:");        try {            File file = new File(fileName);            if (!file.exists()) {                file.createNewFile();            }            reader = new FileReader(file);            char[] buffer = new char[1024];            int charread = 0;            while ((charread = reader.read(buffer)) != -1) {                System.out.print(buffer);            }        } catch (IOException e) {            // TODO: handle exception        } finally {            try {                if (reader != null) {                    reader.close();                }            } catch (IOException e) {                // TODO Auto-generated catch block                e.printStackTrace();            }        }    }    /**     * 字符流：FileWriter     */    public static void writeByFileReader(String output) {        try {            String data = " This content will append to the end of the file";            File file = new File(output);            if (!file.exists()) {                file.createNewFile();            }            FileWriter fileWritter = new FileWriter(file.getName(), true);            fileWritter.write(data);            fileWritter.close();        } catch (IOException e) {            e.printStackTrace();        }    }    /** 缓冲字符流 BufferedReader BufferedWriter     *      * @param fileName     */    public static void readByBufferedReader(String fileName) {        System.out.println("BufferedReader:");        try {            File file = new File(fileName);            // 读取文件，并且以utf-8的形式写出去            BufferedReader bufread;            String read;            bufread = new BufferedReader(new FileReader(file));            while ((read = bufread.readLine()) != null) {                System.out.println(read);            }            bufread.close();        } catch (FileNotFoundException ex) {            ex.printStackTrace();        } catch (IOException ex) {            ex.printStackTrace();        }    }    public static void writeByBufferedReader(String output) {        try {            String content = "This is the content to write into file";            File file = new File(output);            if (!file.exists()) {                file.createNewFile();            }            FileWriter fw = new FileWriter(file, true);            BufferedWriter bw = new BufferedWriter(fw);            bw.write(content);            bw.flush();            bw.close();        } catch (IOException e) {            e.printStackTrace();        }    }}

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