零、前言

1.字符流只能操作文本
2.本质底层依然是使用字节操作，只不过坐了一层封装
3.字符流是由Java虚拟机将字节转化为2个字节的Unicode字符为单位的字符而成的，对多国语言支持性比较好

一、字符流之FileWriter和FileReader

1.字符流之FileWriter的使用

注：new FileWriter(fileName,true) 追加模式添加数据

FileWriter fileWriter = null;
try {String fileName = "I:\\Java\\Base\\Thinking\\src\\IOTest\\FileWriter.txt";//1.创建一个输出流--写出文件：需明确被操作文件----文件不存在,会自动创建文件(同名覆盖)fileWriter = new FileWriter(fileName);//2.写入数据fileWriter.write("Line1 第一行\r\n");//3.刷新流中的缓冲fileWriter.flush();fileWriter.write("Line2 第二行");//获取文件编码格式
System.out.println(fileWriter.getEncoding());//UTF8
} catch (IOException e) {e.printStackTrace();
} finally {//4.关闭流也会刷新缓冲try {//不为空,才能关闭流if (fileWriter != null) {fileWriter.close();}} catch (IOException e) {e.printStackTrace();}
}

FileWriter.png

2.字符流之FileReader的使用

注：为了简单起见，将FileWriter.txt中的Line2 第二行删除

public class Client {public static void main(String[] args) {String fileName = "I:\\Java\\Base\\Thinking\\src\\IOTest\\FileWriter.txt";try {//1.创建一个输入流--读取文件FileReader fileReader = new FileReader(fileName);//2.读取字符//readOneByOne(fileReader);//一个一个读//readOneByWhile(fileReader);//循环一个一个读//readByCharArray(fileReader);//字符数组读取//readByCharArrayByWhile(fileReader);///字符数组循环读取fileReader.close();} catch (IOException e) {e.printStackTrace();}}

1).read()方法，一次读一个字符

private static void readOneByOne(FileReader fileReader) throws IOException {int ch1 = fileReader.read();System.out.println(ch1 + "=" + (char) ch1);//76=Lint ch2 = fileReader.read();System.out.println(ch2 + "=" + (char) ch2);//105=iint ch3 = fileReader.read();System.out.println(ch3 + "=" + (char) ch3);//110=nint ch4 = fileReader.read();System.out.println(ch4 + "=" + (char) ch4);//101=eint ch5 = fileReader.read();System.out.println(ch5 + "=" + (char) ch5);//49=1int ch6 = fileReader.read();System.out.println(ch6 + "=" + (char) ch6);//32=int ch7 = fileReader.read();System.out.println(ch7 + "=" + (char) ch7);//31532=第int ch8 = fileReader.read();System.out.println(ch8 + "=" + (char) ch8);//19968=一int ch9 = fileReader.read();System.out.println(ch9 + "=" + (char) ch9);//34892=行int ch10 = fileReader.read();System.out.println(ch10 + "=" + (char) ch10);//-1 //结束标志
}

read.png

2).循环读取

可见一个一个读十分麻烦，既然有结束标识，每次read()都会走到下一个位置，很像迭代器模式

 private static void readOneByWhile(FileReader fileReader) throws IOException {int ch = 0;while ((ch = fileReader.read()) != -1) {System.out.println(ch + "=" + (char) ch);}}

结果

76=L
105=i
110=n
101=e
49=1
32=
31532=第
19968=一
34892=行

3).使用字符数组读取

private static void readByCharArray(FileReader fileReader) throws IOException {//字符数组char[] buf = new char[8];int len = fileReader.read(buf);System.out.println("len=" + len + "---->" + new String(buf));//len=8---->Line1 第一char[] buf2 = new char[8];int len2 = fileReader.read(buf2);System.out.println("len=" + len2 + "---->" + new String(buf2));//len=3---->行\r\nchar[] buf3 = new char[8];int len3 = fileReader.read(buf3);System.out.println("len=" + len3 + "---->" + new String(buf3));//len=-1---->读完后len为-1
}

4).使用字符数组循环读取

private static void readByCharArrayByWhile(FileReader fileReader) throws IOException {//字符数组循环读取char[] buf = new char[8];int len = 0;while ((len = fileReader.read(buf)) != -1) {System.out.println(new String(buf, 0, len));//Line1 第一//行}
}

read.png

二、使用字符流FileWriter和FileReader拷贝文件

/*** 作者：张风捷特烈* 时间：2018/10/9 0009:12:47* 邮箱：1981462002@qq.com* 说明：将 I:\Java\Base\Thinking\src\IOTest\Activity.md*      拷贝到 F:\javaTest\IO 文件夹中*/
public class Copy {public static void main(String[] args) {FileWriter fileWriter = null;FileReader fileReader = null;try {//创建一个输出流--写出文件:到F:\javaTest\IO\Activity.mdfileWriter = new FileWriter("F:\\javaTest\\IO\\Activity.md");//创建一个输入流--读取文件：I:\Java\Base\Thinking\src\IOTest\Activity.mdfileReader = new FileReader("I:\\Java\\Base\\Thinking\\src\\IOTest\\Activity.md");int len = 0;//读取的长度char[] buf = new char[1024];//2K的字符数组while ((len = fileReader.read(buf)) != -1) {fileWriter.write(buf, 0, len);//写有效个字符}} catch (IOException e) {throw new RuntimeException("读取失败");}finally {try {//关闭输入流if (fileReader != null) {fileReader.close();}} catch (IOException e) {e.printStackTrace();}try {//关闭输出流if (fileWriter != null) {fileWriter.close();}} catch (IOException e) {e.printStackTrace();}}}
}

三、字符缓冲：BufferedWriter和BufferedReader

将字符读入内存缓冲区，避免频繁执行读写操作，提高流的操作效率默认字符数组缓冲区大小：8192 (即16K的缓冲)

1.BufferedWriter：缓存写出

BufferedWriter bfw = null;
try {String fileName = "I:\\Java\\Base\\Thinking\\src\\IOTest\\BufferedWriter.txt";//1.创建一个输出流--写出文件：需明确被操作文件----文件不存在,会自动创建文件(同名覆盖)bfw = new BufferedWriter(new FileWriter(fileName));//2.写入数据bfw.write("Line1 第一行");bfw.newLine();//换行 BufferedWriter特有方法，可区分不同平台换行//3.刷新流中的缓冲bfw.flush();bfw.write("Line2 第二行");
} catch (IOException e) {e.printStackTrace();
} finally {//4.关闭流也会刷新缓冲try {//不为空,才能关闭流if (bfw != null) {bfw.close();}} catch (IOException e) {e.printStackTrace();}
}

2.BufferedReader:缓存读取

public static void main(String[] args) {String fileName = "I:\\Java\\Base\\Thinking\\src\\IOTest\\Activity.md";try {//1.创建一个输入流--读取文件BufferedReader  bfr= new BufferedReader(new FileReader(fileName));//2.读取字符//读取一行：BufferedReader特有方法String line = null;while ((line = bfr.readLine()) != null) {System.out.println(line);}bfr.close();} catch (IOException e) {e.printStackTrace();}
}

四、效率测试

通过读取一个1275K的文件看时间消耗情况

/*** 一个一个字符读取测试** @param fileName* @return*/
private static String readOneByOne(String fileName) {FileReader fileReader = null;try {StringBuilder sb = new StringBuilder();fileReader = new FileReader(fileName);int ch = 0;while ((ch = fileReader.read()) != -1) {sb.append(new String((new char[]{(char) ch})));}return sb.toString();} catch (Exception e) {e.printStackTrace();return null;} finally {try {if (fileReader != null) {fileReader.close();}} catch (IOException e) {e.printStackTrace();}}
}

    /*** 字符数组效率测试** @param fileName* @return*/private static String readByArray(String fileName) {FileReader fileReader = null;try {StringBuilder sb = new StringBuilder();fileReader = new FileReader(fileName);int len = 0;char[] buf = new char[1024];while ((len = fileReader.read(buf)) != -1) {sb.append(new String(buf, 0, len));}return sb.toString();} catch (Exception e) {e.printStackTrace();return null;} finally {try {if (fileReader != null) {fileReader.close();}} catch (IOException e) {e.printStackTrace();}}}

    /*** BufferedReader效率测试** @param fileName* @return*/private static String readByBuffer(String fileName) {BufferedReader bfr = null;try {StringBuilder sb = new StringBuilder();bfr = new BufferedReader(new FileReader(fileName));String line = null;while ((line = bfr.readLine()) != null) {sb.append(line);}return sb.toString();} catch (Exception e) {e.printStackTrace();return null;} finally {try {if (bfr != null) {bfr.close();}} catch (IOException e) {e.printStackTrace();}}}

后记：捷文规范

1.本文成长记录及勘误表

2.更多关于我

3.声明

1----本文由张风捷特烈原创,转载请注明
2----欢迎广大编程爱好者共同交流
3----个人能力有限，如有不正之处欢迎大家批评指证，必定虚心改正
4----看到这里，我在此感谢你的喜欢与支持