黑马程序员之JAVAIO(一)

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一、概述

        IO流用来处理设备之间的数据传输。按操作的数据分为：字节流和字符流；按流向分为：输入流和输出流。

        在JAVA中字节流的抽象基类为：OutputStream和InputStream；字符流的抽象基类为：Reader和Writer。

二、Reader字符读取流，读取文字类文件。

        示例一：

import java.io.FileReader;import java.io.IOException;public class FileReaderDemo {public static void main(String[] args) throws IOException {//创建一个文件读取流对象, 并指定要读取的文件//要保证文件的存在, 否则会报FileNotFindExcptionFileReader fr = new FileReader("D:/dome2.txt");//read()读取字符, 每次读取一个, 读完了返回-1int ch = 0;while (-1 != (ch = fr.read())) {System.out.println((char)ch);}fr.close();}}

        示例二：

import java.io.FileReader;import java.io.IOException;/* * 通过字符数组进行读取 */public class FileReaderDemo2 {public static void main(String[] args) throws IOException {FileReader fr = new FileReader("D:/dome2.txt");// 定义数组, 用于存储读到的字符char[] buffer = new char[512];// int num = fr.read(buffer); 返回读取的个数StringBuffer sb = new StringBuffer();int num = 0;while (-1 != (num = fr.read(buffer))) {sb.append(new String(buffer, 0, num));}fr.close();System.out.println(sb.toString());}}

        示例三：

//将一个.java文件读取出来, 并打印到控制台public class FileReaderTest {public static void main(String[] args) throws IOException {FileReader fr = new FileReader("D:/CalendarDemo.java");char[] buffer = new char[5];int num =0 ;StringBuffer sb = new StringBuffer();while(-1 != (num = fr.read(buffer))){sb.append(new String(buffer,0,num));}System.out.println(sb.toString());fr.close();}}

三、Writer字符输出流。

        示例一：

public class FileWriterDemo {public static void main(String[] args) throws IOException {//创建一个FileWriter对象, 该对象一被初始化就必须明确被操作的文件//该文件被创建在指定的目录下, 如果该目录下已经有同名的文件, 将会被覆盖FileWriter fw = new FileWriter("D:/dome.txt");//将数据写入到流中fw.write("313111");//刷新流对象换缓冲数据, 将数据刷到目的地中fw.flush();//刷新缓冲数据, 并且将流关闭fw.close();}}

        示例二：

/* * 文件续写 */public class FileWriterDemo3 {public static void main(String[] args) {FileWriter fw = null;try {//传递true参数, 表示不会覆盖已有的文件, 并且在文件的后面续写数据fw = new FileWriter("D:/dome2.txt", true);//windows下换行fw.write("121\r\nmmmmm");fw.flush();} catch (Exception e) {System.out.println(e.toString());} finally {try {if (null != fw)fw.close();} catch (IOException e) {e.printStackTrace();}}}}

四、为了提高文件输入和输出流的效率， Java提供了一个增强的功能，那就是流缓冲区， BufferedReader和BufferedWriter。

        示例一：

//字符读取流缓冲区public class BufferedReaderDemo {public static void main(String[] args) throws IOException {//创建一个读取流对象FileReader fr = new FileReader("D:/buffer.txt");//将字符读取流对象作为参数传给缓冲区对象BufferedReader br = new BufferedReader(fr);String line = null;StringBuffer sb = new StringBuffer();//readLine() //读取一行文本, 只会读取回车之前的字符, 不会返回回车//无论是读取一行还是多个字符, 最终还是使用的read()方法, 一个一个的读取while (null != (line = br.readLine())) {sb.append(line);}System.out.println(sb.toString());br.close();}}

        示例二：

//缓冲区是为了提高流的操作效率//所以在创建缓冲区之前必须要有流对象public class BufferedWriterDemo {public static void main(String[] args) throws IOException {//创建一个字符写入流FileWriter fw = new FileWriter("D:/buffer.txt");//为了提高写入流的效率, 加入缓冲区//把流对像作为参数传给缓冲区构造函数即可BufferedWriter bw = new BufferedWriter(fw);bw.write("1aad");for(int i=0;i<3;i++){bw.write("adad" + i);bw.newLine();//换行, 兼容各个系统bw.flush();}bw.flush();//关闭缓冲区, 就是在关闭缓冲区中的流对象bw.close();fw.close();}}

        示例三：

/* * 从C盘拷贝一个文件到D盘 * 运用BufferedReader和BufferedWriter */public class CopyTextByBuffered {public static void main(String[] args) {String srcPath = "C:/FaceProv.log";String descPath = "D:/FaceProv.log";CopyTextByBuffered.copy(srcPath, descPath);}public static void copy(String srcPath, String descPath) {FileReader fr = null;FileWriter fw = null;BufferedReader br = null;BufferedWriter bw = null;try {fr = new FileReader(srcPath);fw = new FileWriter(descPath);br = new BufferedReader(fr);bw = new BufferedWriter(fw);int len = 0;char[] buffer = new char[20];while (-1 != (len = br.read(buffer))) {bw.write(buffer, 0, len);bw.flush();}} catch (Exception e) {throw new RuntimeException("拷贝失败 !");} finally {if (null != br)try {br.close();} catch (IOException e) {e.printStackTrace();}if (null != bw)try {bw.close();} catch (IOException e) {e.printStackTrace();}}}}

五、FileOutputStream字节输出流。

        示例：

//将一个字符串写入到D盘文件中public static void writer() throws IOException{FileOutputStream fos = new FileOutputStream("D:/fos.txt");fos.write("aaad".getBytes());fos.close();}

六、FileInputStream字节输入流。

        示例：

//一个一个读public static void reader() throws IOException{FileInputStream fis = new FileInputStream("D:/fos.txt");int ch =0;while(-1 != (ch = fis.read())){System.out.println((char)ch);}fis.close();}public static void reader2() throws IOException{FileInputStream fis = new FileInputStream("D:/fos.txt");byte[] b = new byte[20];int len = 0;while(-1 != (len = fis.read(b))){System.out.println(new String(b,0,len));}fis.close();}public static void reader3() throws IOException{FileInputStream fis = new FileInputStream("D:/fos.txt");int size = fis.available();//返回文件中字节数大小byte[] b = new byte[size];//定义一个刚好大小的缓冲区, 不用在循环, 此方式不适合读取大文件fis.read(b);System.out.println(new String(b));fis.close();}

七、同样的字节流也有缓冲区的，就是BufferedOutputStream和BufferedInputStream，下面的示例就是利用字节流的缓冲区拷贝一个

        mp3文件。

        示例：

//拷贝一个MP3文件public static void copyMp3(String srcPath, String descPath){BufferedOutputStream bos = null;BufferedInputStream bis = null;try {bos = new BufferedOutputStream(new FileOutputStream(descPath));bis = new BufferedInputStream(new FileInputStream(srcPath));int b = 0;while(-1 != (b = bis.read())){bos.write(b);}} catch (Exception e) {throw new RuntimeException("拷贝失败");}finally {if(null != bis)try {bis.close();} catch (IOException e) {throw new RuntimeException("关闭读取流失败");}if(null != bos)try {bos.close();} catch (IOException e) {throw new RuntimeException("关闭写入流失败");}}}

八、InputStreamReader和OutputStreamWriter转换流

        示例：

//readLine()是字符流BufferedReader类中的方法, 键盘录入的read()则是字节流InputStream类中的方法//可以通过InputStreamReader类来转换//需要注意的是, 只有转换流才可以指定字符的编码集public class TransStreamDemo {public static void main(String[] args) throws IOException {toPrint2();}public static void myPrint() throws IOException {// 获取键盘录入对象InputStream in = System.in;// 将字节流转换成字符流, 需要使用转换流InputStreamReader isr = new InputStreamReader(in);BufferedReader br = new BufferedReader(isr);OutputStream os = System.out;OutputStreamWriter osw = new OutputStreamWriter(os);BufferedWriter bw = new BufferedWriter(osw);String line = null;while (null != (line = br.readLine())) {if ("over".equals(line))break;// System.out.println(line);bw.write(line);bw.newLine();bw.flush();}br.close();bw.close();}// 将控制台的录入, 写入到文件中public static void toFile() throws IOException {BufferedReader br = new BufferedReader(new InputStreamReader(System.in));BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(new FileOutputStream("D:/out.txt")));String line = null;while (null != (line = br.readLine())) {if ("over".equals(line))break;bw.write(line);bw.newLine();bw.flush();}br.close();bw.close();}// 将文件中的数据, 打印到控制台public static void toPrint() throws IOException {BufferedReader br = new BufferedReader(new InputStreamReader(new FileInputStream("D:/out.txt")));BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));String line = null;while (null != (line = br.readLine())) {if ("over".equals(line))break;bw.write(line);bw.newLine();bw.flush();}br.close();bw.close();}// 将文件中的数据, 打印到控制台, 通过改变源public static void toPrint2() throws IOException {//设置标准输入设备System.setIn(new FileInputStream("D:/out.txt"));//设置输出设备//System.setOut(new PrintStream("D:/setout.txt"));BufferedReader br = new BufferedReader(new InputStreamReader(System.in));BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));String line = null;while (null != (line = br.readLine())) {if ("over".equals(line))break;bw.write(line);bw.newLine();bw.flush();}br.close();bw.close();}}