JAVA核心技术I---JAVA基础知识（文本文件读写）

一：java IO包概述

（一）Java读写文件，只能以(数据)流的形式进行读写

（二）java IO 包

–节点类：直接对文件进行读写

–包装类
• 转化类：字节/字符/数据类型的转化类
• 装饰类：装饰节点类

（三）节点类

–InputStream, OutputStream(字节)
　　• FileInputStream,FileOutputStream

–Reader,Writer(字符)
　　• FileReader, FileWriter

（四）转换类：字符到字节之间的转化

–InputStreamReader：文件读取时字节，转化为Java能理解的字符
–OutputStreamWriter：Java将字符转化为字节输入到文件中

（五）装饰类：装饰节点类

–DataInputStream,DataOutputStream: 封装数据流
–BufferedInputStream,BufferOutputStream：缓存字节流
–BufferedReade, BufferedWriter：缓存字符流

二：文本文件读写

–输出文本字符到文件中
–从文件中读取文本字符串

（一）写文件

–先创建文件，写入数据，关闭文件
–FileOutputStream, OutputStreamWriter, BufferedWriter
–BufferWriter
　　• write
　　• newLine
–try-resource 语句，自动关闭资源
–关闭最外层的数据流，将会把其上所有的数据流关闭

    public static void writeFile1() {
        FileOutputStream fos = null;
        OutputStreamWriter osw = null;
        BufferedWriter bw = null;
        try {
            fos = new FileOutputStream("c:/temp/abc.txt"); // 节点类
            osw = new OutputStreamWriter(fos, "UTF-8"); // 转化类
            //osw = new OutputStreamWriter(fos); // 转化类
            bw = new BufferedWriter(osw); // 装饰类
            // br = new BufferedWriter(new OutputStreamWriter(new
            // FileOutputStream("c:/temp/abc.txt")))
            bw.write("我们是");
            bw.newLine();
            bw.write("Ecnuers.^^");
            bw.newLine();
        } catch (Exception ex) {
            ex.printStackTrace();
        } finally {
            try {
                bw.close(); // 关闭最后一个类，会将所有的底层流都关闭
            } catch (Exception ex) {
                ex.printStackTrace();
            }
        }
    }

    public static void writeFile2() {
        //try-resource 语句，自动关闭资源
        try (BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(new FileOutputStream("c:/temp/abc.txt")))) {
            bw.write("我们是");
            bw.newLine();
            bw.write("Ecnuers.^^");
            bw.newLine();
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }

（二）读文件

–先打开文件，逐行读入数据，关闭文件
–FileInputStream, InputStreamWriter, BufferedReade
–BufferReader
　　• readLine
–try-resource 语句，自动关闭资源
–关闭最外层的数据流，将会把其上所有的数据流关闭

    public static void readFile1() {
        FileInputStream fis = null;
        InputStreamReader isr = null;
        BufferedReader br = null;
        try {
            fis = new FileInputStream("c:/temp/abc.txt"); // 节点类
            isr = new InputStreamReader(fis, "UTF-8"); // 转化类
            //isr = new InputStreamReader(fis);
            br = new BufferedReader(isr); // 装饰类
            // br = new BufferedReader(new InputStreamReader(new
            // FileInputStream("c:/temp/abc.txt")))
            String line;
            while ((line = br.readLine()) != null) // 每次读取一行
            {
                System.out.println(line);
            }
        } catch (Exception ex) {
            ex.printStackTrace();
        } finally {
            try {
                br.close(); // 关闭最后一个类，会将所有的底层流都关闭
            } catch (Exception ex) {
                ex.printStackTrace();
            }
        }
    }

    public static void readFile2() {
        String line;
        //try-resource 语句，自动关闭资源
        try (BufferedReader in = new BufferedReader(new InputStreamReader(new FileInputStream("c:/temp/abc.txt")))) {
            while ((line = in.readLine()) != null) {
                System.out.println(line);
            }
        }
        catch(Exception ex)
        {
            ex.printStackTrace();
        }
    }

（三）混用写入和读取

public class FileW {
    public static void main(String[] args) {
        //写文件
        FileOutputStream fos = null;        //节点类
        OutputStreamWriter osw = null;        //转换类
        BufferedWriter bw=null;                //装饰类

        try {
            fos = new FileOutputStream("D:\\MyJava\\Code\\JH16\\test\\aa\\bb\\E.txt");
            osw = new OutputStreamWriter(fos);
            bw = new BufferedWriter(osw);

            //开始写入
            bw.write("我们是：");
            bw.newLine();
            bw.write("fwawa!");
            bw.newLine();
        }catch(Exception e) {
            System.err.println(e.getMessage());
        }finally{
            try {
                bw.close();
            }catch(Exception e) {
                System.err.println(e.getMessage());
            }
        }

        //读取文件
        String line;
        try(BufferedReader in =
                new BufferedReader(
                        new InputStreamReader(
                                new FileInputStream("D:\\MyJava\\Code\\JH16\\test\\aa\\bb\\E.txt")))){
            while((line=in.readLine())!=null) {
                System.out.println(line);
            }
        }catch(Exception e) {
            System.err.println(e.getMessage());
        }
    }
}

我们是：
fwawa!