IO流——字节流和字符流基本使用

版权声明：作者：changshuchao https://blog.csdn.net/changshuchao/article/details/89096128

字节流示例

/*字节流*/
public class TestByteStream {

    public static void main(String[] args) throws IOException {

//        testFileOutputStream();
//        testFileInputStream();
        copyContentFormSource2Target();

    }

    public static void testFileOutputStream() throws IOException {
        //1、创建目标对象，输出流表示把数据保存到哪个文件。不写盘符，默认该文件是在该项目的根目录下
        File file  = new File("io"+File.separator+"test.txt");
        System.out.println(file.getAbsolutePath());
        if(!file.exists()){
            file.createNewFile();
        }
        OutputStream outputStream = null;
        try {
            //2、创建文件的字节输出流对象,第二个参数是 Boolean 类型，true 表示后面写入的文件追加到数据后面，false 表示覆盖
            outputStream = new FileOutputStream(file,false);
            outputStream.write(65);
            outputStream.write("csc".getBytes());
            outputStream.write("helloworld".getBytes(),1,4);

        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } finally {
            if(outputStream != null){
                outputStream.close();
            }
        }

    }

    public static void testFileInputStream() throws IOException {
        File source = new File("io"+File.separator+"test.txt");
        InputStream inputStream = null;
        try {
            System.out.println("【测试1】");
            inputStream = new FileInputStream(source);
            int data1 = inputStream.read();
            System.out.println((char)data1);

            System.out.println("【测试2】");
            byte[] data2 = new byte[10];
            int numBytesRead = inputStream.read(data2);
            System.out.println(Arrays.toString(data2));
            System.out.println(new String(data2));
            System.out.println(numBytesRead);

            System.out.println("【测试3】");
            int num = inputStream.read(data2,0,3);
            System.out.println(Arrays.toString(data2));
            System.out.println(new String(data2));
            System.out.println(num);



        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }finally {
            inputStream.close();
        }
    }

    public static void copyContentFormSource2Target() throws IOException {
        File source = new File("io"+File.separator+"source.txt");
        File target = new File("io"+File.separator+"target.txt");
        if(!source.exists()){
            source.createNewFile();
        }
        if(!target.exists()){
            target.createNewFile();
        }

        InputStream input = new FileInputStream(source);
        OutputStream out = new FileOutputStream(target);

        byte[] data = new byte[10];

//        int available = Math.min(10,input.available());
//        while (available > 0){
//            input.read(data,0,available);
//            out.write(data,0,available);
//            available = Math.min(10,input.available());
//        }
        int len;
        while((len = input.read(data))!=-1){
            out.write(data,0,len);
        }


        input.close();
        out.close();
    }
}

上述代码作用是将文本写入项目目录下的io子目录下的txt文件，然后从中读取。

字符流示例

/*字符流*/
public class TestCharStream {

    public static void main(String[] args) throws IOException {
//        testWriter();
        testReader();
//        copyFile();
    }


    private static void testWriter() throws IOException {
        File file = new File("io"+File.separator+"sourceWriter.txt");
        if(!file.exists()){
            file.createNewFile();
        }

        FileWriter writer = new FileWriter(file);
        writer.write(65);
        writer.write("我是");
        writer.write("changshuchao".toCharArray());
        writer.write(",helloa",0,6);
        writer.write(",nice to meet you , haha".toCharArray(),0,17);

        /***
         * 注意如果这里有一个 缓冲的概念，如果写入文件的数据没有达到缓冲的数组长度，那么数据是不会写入到文件中的
         * 解决办法：手动刷新缓冲区 flush()
         * 或者直接调用 close() 方法，这个方法会默认刷新缓冲区
         */
        writer.flush();
        writer.close();
    }

    private static void testReader() throws IOException {
        File file = new File("io"+File.separator+"sourceWriter.txt");
        if(!file.exists()){
            file.createNewFile();
        }

        FileReader reader = new FileReader(file);

        int len;
        while((len = reader.read())!= -1){
            System.out.println((char)len);
        }
        System.out.println("~~~~~~~~~~~~~~~~~~~~~~~~~~~");

        char[] data = new char[10];
        while((len = reader.read(data)) != -1){
            System.out.println("["+new String(data,0,len)+"]");
        }
        System.out.println("~~~~~~~~~~~~~~~~~~~~~~~~~~~");

        while((len = reader.read(data,0,10))!= -1){
            System.out.println(new String(data,0,len));
        }

    }

    private static void copyFile() throws IOException {
        File source = new File("io"+File.separator+"sourceWriter.txt");
        if(!source.exists()){
            source.createNewFile();
        }

        File target = new File("io"+File.separator+"targetWriter.txt");
        if(!target.exists()){
            target.createNewFile();
        }

        FileReader reader = new FileReader(source);
        FileWriter writer = new FileWriter(target);

        int len = -1;
        char[] data = new char[10];
        while((len = reader.read(data))!=-1){
            writer.write(data,0,len);
        }

        reader.close();
        writer.close();


    }

}