Java IO流 字符流 與 轉換流 詳解

字符流

一個字符字符的讀 只能用來操作文本(不能寫其他格式)

字符輸出流(Writer)

寫入字符流的抽象類

實現子類 FileWriter
代碼示例:

public class Demo04 {
    public static void main(String[] args) throws IOException {
        FileWriter fWriter = new FileWriter("/Users/james/Desktop/level/haha.txt");
        fWriter.write(100);
        // 注意 字符輸出流 在寫入文件的時候需要調用刷新方法
        // 建議 每次寫入最好都刷新一次
        fWriter.flush();
        char[] c = {'l','o','n','g'};
        fWriter.write(c);
        fWriter.flush();
        fWriter.write(c, 1,3);
        fWriter.flush();
        // 使用字符串直接寫入
        fWriter.write("抽刀斷水水更流\n");
        fWriter.flush();
        fWriter.write("借酒消愁愁更愁\n");
        fWriter.flush();
        fWriter.write("百日依山盡", 1, 2);
        // 關閉資源前 刷新
        fWriter.close();
    }
}

字符輸入流(Reader)

用於讀取字符流的抽象類

實現子類:FileReader
代碼示例:

public class Demo05 {
    public static void main(String[] args) throws IOException {
        FileReader reader = new FileReader("/Users/james/Desktop/level/haha.txt");
        // 循環讀取
        char[] bs = new char[1024];
        int len = 0;
        while ((len = reader.read(bs)) != -1) {
            System.out.println(new String(bs, 0, len));
        }
        reader.close();
    }
}

字符流中輸出流中可以直接寫字符串類型 但是輸入流纔行 這是爲什麼呢?

因爲字符串類型很難判斷什麼時候結束 因此輸入流不能直接讀字符串

例題聯繫:

利用字符流複製文件

public class Demo06 {
    public static void main(String[] args) {

        File file = new File("/Users/james/Desktop/level/haha.txt");
        File file2 = new File("/Users/james/Desktop/level/ha.txt");
        copyFileTxt(file, file2);

    }

    // 字符流複製文件
    public static void copyFileTxt(File src ,File dest) {
        FileReader reader = null;
        FileWriter writer = null;

        try {
            reader = new FileReader(src);
            writer = new FileWriter(dest);
            char[] c = new char[1024];
            int len = 0;
            while ((len = reader.read(c)) != -1) {
                writer.write(c, 0, len);
            }               
        } catch (FileNotFoundException e) {
            throw new RuntimeException("找不到文件");
        } catch (IOException e) {
            throw new RuntimeException("編譯異常");
        }finally {
            try {
                if (reader != null) {
                    reader.close();
                }               
            } catch (IOException e) {
                throw new RuntimeException("資源關閉異常");
            }finally {
                try {
                    if (writer != null) {
                        writer.close();
                    }
                } catch (IOException e) {
                    throw new RuntimeException("資源關閉異常");
                }
            }
        }
    }
}

轉換流

OutputStreamWriter(字符流轉向字節流)

字符流轉向字節流 可以使用不同編碼格式寫入 需要使用到FileOutStream類

InputStreamReader(字節流轉向字符流)

可以讀取不同編碼格式的文件 需要使用到 FileInputStream類

代碼示例:

public class Demo07 {
    public static void main(String[] args) throws IOException {
        //getUTF8();
//      getGBK();
//      readUTF8();
        readGBK();
    }

    // 利用轉換流寫文件 OutputStreamWriter 默認UTF-8寫
    public static void getUTF8() throws IOException {
        FileOutputStream fos = new FileOutputStream("/Users/james/Desktop/level/utf-8.txt");
        // 創建轉換流 字符流轉向字節流
        OutputStreamWriter osw = new OutputStreamWriter(fos);
        // 寫文件
        osw.write("雪中智代雨中杏,櫻下小渚花田汐");
        // 關閉資源(只關閉外層流 就可以)
        osw.close();

    }
    // 利用轉換流寫文件 OutputStreamWriter 使用GBK
    public static void getGBK() throws IOException {
            FileOutputStream fos = new FileOutputStream("/Users/james/Desktop/level/GBK.txt");
        // 構建轉換流 傳入編碼格式(編碼格式的字符串 忽略大小寫)
        OutputStreamWriter osw = new OutputStreamWriter(fos, "GBK");
        osw.write("雪中智代雨中杏,櫻下小渚花田汐");
        osw.close();    
    }

    public static void readUTF8() throws IOException {
        FileInputStream fis = new FileInputStream("/Users/james/Desktop/level/utf-8.txt");
        InputStreamReader isr = new InputStreamReader(fis); 
        int len = 0;
        char[] b = new char[1024];
        while ((len = isr.read(b)) != -1) {
            System.out.println(new String(b, 0, len));
        }

        isr.close();
    }

    public static void readGBK() throws IOException {
        FileInputStream fis = new FileInputStream("/Users/james/Desktop/level/GBK.txt");
        InputStreamReader isr = new InputStreamReader(fis,"GBK"); 
        int len = 0;
        char[] b = new char[1024];
        while ((len = isr.read(b)) != -1) {
            System.out.println(new String(b, 0, len));
        }
        isr.close();
    }
}