IO流相关代码整合

简单整理一下IO的知识,如有问题还望指出。

流根据不同维度可以分为  输入流和输出流 、字节流和字符流;输入流为读取信息,输出流为写入信息;字节流是以字节为单位读取,字符流是按字符为单位读取(可以是一个汉字也可以是一个字母、数字、符号等);一般使用字节流比较多,字符流个人认为应该是在按字符处理的时候使用,其他情况均可使用字节流。

*简单说明一下 位(bit)、字节(byte)、字符(char)之间的关系

1byte = 8bit;

1字符 = 1byte 或 2byte;

下面整理了一下IO的相关操作方法,里面大概的基础知识点都可以覆盖,代码如下:

package com.sr;

import java.io.*;

/**
 * Created by sr on 2018/7/21.
 */
public class IO {

    private static final String fileName = "qianming.lic";

    public static void main(String[] args) {
        byte[] bytes1 = getBytesByFileName1(fileName);
        byte[] bytes2 = getBytesByFileName2(fileName);
        byte[] bytes3 = getBytesByFileName3(fileName);

        System.out.println(bytes1.length);
        System.out.println(bytes2.length);
        System.out.println(bytes3.length);


        InputStream inputStream = getInputStreamByString(fileName);
        byte[] bytes4 = getBytesByInputStream(inputStream);

        System.out.println("bytes4");
        System.out.println(new String(bytes4));

        String string1 = getStringByFileName(fileName);

        System.out.println("string1");
        System.out.println(string1);

        String string2 = getStringByFileName2(fileName);

        System.out.println("string2");
        System.out.println(string2);

        String string3 = getStringByFileName3(fileName);

        System.out.println("string3");
        System.out.println(string3);

        file2file(fileName,"testNewFile");

    }


    /**
     *  读取文件获取字节数组1
     * @param fileName
     * @return
     */
    public static byte[] getBytesByFileName1(String fileName){
        try {
            InputStream inputStream = new FileInputStream(fileName);
            ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
            int data = 0;
            while ((data = inputStream.read()) != -1){
                byteArrayOutputStream.write(data);
            }
            return byteArrayOutputStream.toByteArray();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;
    }

    /**
     *  读取文件获取字节数组2
     * @param fileName
     * @return
     */
    public static byte[] getBytesByFileName2(String fileName){
        try {
            InputStream inputStream = new FileInputStream(fileName);
            ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
            int readLength = 1024;
            byte[] bytes = new byte[readLength];
            int len = 0;
            while ((len = inputStream.read(bytes,0,readLength)) != -1){
                byteArrayOutputStream.write(bytes,0,len);
            }
            return byteArrayOutputStream.toByteArray();//byteArrayOutputStream.toString() 可以直接返回字节数组转换的字符串
        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;
    }

    /**
     *  读取文件获取字节数组3
     * @param fileName
     * @return
     */
    public static byte[] getBytesByFileName3(String fileName){
        try {
            InputStream inputStream = new FileInputStream(fileName);
            ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
            int readLength = 200;
            byte[] bytes = new byte[readLength];
            int len = 0;
            while ((len = inputStream.read(bytes)) != -1){
//                byteArrayOutputStream.write(bytes);//可能导致写入的长度多
                byteArrayOutputStream.write(bytes,0,len);
            }
            return byteArrayOutputStream.toByteArray();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;
    }

    /**
     * 将输入流转换为字节数组
     * @param inputStream
     * @return
     */
    public static byte[] getBytesByInputStream(InputStream inputStream){
        try {
            ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
            int readLength = 1024;
            byte[] bytes = new byte[readLength];
            int len = 0;
            while ((len = inputStream.read(bytes,0,readLength)) != -1){
                byteArrayOutputStream.write(bytes,0,len);
            }
            return byteArrayOutputStream.toByteArray();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;
    }

    /**
     * 将字符串转为输入流
     * @param str
     * @return
     */
    public static InputStream getInputStreamByString(String str){
        try {
            ByteArrayInputStream inputStream = new ByteArrayInputStream(str.getBytes());
            return inputStream;
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }

    /**
     * 字节流读取文件内容
     * @param fileName
     * @return
     */
    public static String getStringByFileName(String fileName){
        try {
            return new String(getBytesByFileName2(fileName));
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }

    /**
     * 字符流读取文件内容
     * @param fileName
     * @return
     */
    public static String getStringByFileName2(String fileName){
        try {
            InputStream inputStream = new FileInputStream(fileName);
            InputStreamReader inputStreamReader = new InputStreamReader(inputStream);
            String string = "";
            int i = inputStreamReader.read();
            while (i != -1) {
                string += ((char)i);
                i = inputStreamReader.read();
            }
            return string;
        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;
    }


    /**
     * 字符流读取文件内容 按行读
     * @param fileName
     * @return
     */
    public static String getStringByFileName3(String fileName){
        try {
            InputStream inputStream = new FileInputStream(fileName);
            InputStreamReader inputStreamReader = new InputStreamReader(inputStream);
            BufferedReader bufferedReader = new BufferedReader(inputStreamReader);
            String string = null;
            StringBuffer stringBuffer = new StringBuffer();
            boolean isFirst = true;
            while ((string = bufferedReader.readLine()) != null) {
                if (!isFirst){
                    stringBuffer.append(System.getProperty("line.separator"));//添加换行符
                }
                isFirst = false;
                stringBuffer.append(string);
            }
            return stringBuffer.toString();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;
    }

    /**
     * 字节流复制文件并写入文件
     * 复制文件
     * @param oldFileName
     * @param newFileName
     */
    public static void file2file(String oldFileName,String  newFileName){
        try {
            FileInputStream fileInputStream = new FileInputStream(oldFileName);
            FileOutputStream fileOutputStream = new FileOutputStream(newFileName);
            int data = 0;
            while ((data = fileInputStream.read()) != -1){
                fileOutputStream.write(data);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

}

 

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