缓冲流(BufferedOutputStream BufferedInputStream BufferedWriter BufferedReader)
原理:在创建流对象时,在内存中会创建一个默认大小的缓冲数组,在读写时,先将数据写在缓冲数组中,再将缓冲数组交给系统-JVM,减少了系统读写次数,从而提高了读写效率
这跟用数组进行read(byte[] b)和write(byte[] b)差不多
BufferedOutputStream类 extends OutputStream-----字节缓冲输出流
构造方法:
public BufferedOutputStream(OutputStream out) ---缓冲数组默认为8192
public BufferedOutputStream(OutputStream out, int size) ---size设置缓冲数组的大小
使用步骤:
1.创建一个继承了OutputStream的类的对象,构造方法中绑定要输出的目的地
2.创建BufferedOutputStream对象,构造方法中传递继承了OutputStream的类的对象
3.使用BufferedOutputStream对象的write方法,写数据
4.使用BufferedOutputStream对象中flush方法,将内存中缓冲数组的数据,刷新到文件中去
5.释放资源(会先调用flush方法,刷新数据,4可省略,直接关闭BufferedOutputStream,OutputStream会自动关闭)
package iotest.bufferedIOtest; import java.io.BufferedOutputStream; import java.io.FileOutputStream; import java.io.IOException; public class BufferedOutputStreamTest01 { public static void main(String[] args) throws IOException { FileOutputStream fos = new FileOutputStream("src\\iotest\\bufferedIOtest\\a.txt"); BufferedOutputStream bos = new BufferedOutputStream(fos); bos.write(97); bos.flush(); fos.close(); bos.close(); } }
BufferedInputStream 类extends InputStream ---字节缓冲输入流
构造方法:
public BufferedInputStream(InputStream in)---缓冲数组默认为8192
public BufferedInputStream(InputStream in, int size) --size设置缓冲数组的大小
使用步骤:
1.创建一个继承了InputStream 的类的对象,构造方法中绑定要读取的文件的地址
2.创建BufferedInputStream 对象,构造方法中传递继承了InputStream 的类的对象
3.使用BufferedInputStream 对象的read方法,读数据
4.释放资源(直接关闭BufferedOutputStream,OutputStream会自动关闭)
package iotest.bufferedIOtest; import java.io.BufferedInputStream; import java.io.FileInputStream; import java.io.IOException; public class BufferedInputStreamTest01 { public static void main(String[] args) throws IOException { FileInputStream fis = new FileInputStream("src\\iotest\\bufferedIOtest\\a.txt"); BufferedInputStream bis = new BufferedInputStream(fis); //一次读取一个字节 /*int len = 0; while ((len = bis.read()) != -1){ System.out.print((char)len); }*/ //运用数组,一次读取多个字节 int len = 0; byte[] bytes = new byte[1024]; while ((len = bis.read(bytes)) != -1){ System.out.println(new String(bytes)); } bis.close(); } }
不同方式复制文件的效率比较
package iotest.bufferedIOtest.copytest; import java.io.FileInputStream; import java.io.FileOutputStream; import java.io.IOException; //运用字节流,一次读取一个字节,来复制文件 //文件复制共用了429毫秒 public class Copy1 { public static void main(String[] args) throws IOException { long startTime = System.currentTimeMillis(); FileInputStream fis = new FileInputStream("C:\\test\\1.jpg"); FileOutputStream fos = new FileOutputStream("D:\\test\\1.jpg"); int len = 0; while ((len = fis.read()) != -1){ fos.write(len); } fos.close(); fis.close(); long endTime = System.currentTimeMillis(); System.out.println("文件复制共用了"+(endTime-startTime)+"毫秒"); } }
package iotest.bufferedIOtest.copytest; import java.io.FileInputStream; import java.io.FileOutputStream; import java.io.IOException; //运用字节流,运用字节数组来读取文件 //文件复制共用了11毫秒 public class Copy2 { public static void main(String[] args) throws IOException { long startTime = System.currentTimeMillis(); FileInputStream fis = new FileInputStream("C:\\test\\1.jpg"); FileOutputStream fos = new FileOutputStream("D:\\test\\1.jpg"); int len = 0; byte[] bytes = new byte[1024]; while ((len = fis.read(bytes)) != -1){ fos.write(bytes,0,len); } fos.close(); fis.close(); long endTime = System.currentTimeMillis(); System.out.println("文件复制共用了"+(endTime-startTime)+"毫秒"); } }
package iotest.bufferedIOtest.copytest; import java.io.*; //运用字节缓冲流,一次读写一个字节,来复制文件 //文件复制共用了14毫秒 public class Copy3 { public static void main(String[] args) throws IOException { long startTime = System.currentTimeMillis(); FileInputStream fis = new FileInputStream("C:\\test\\1.jpg"); FileOutputStream fos = new FileOutputStream("D:\\test\\1.jpg"); BufferedInputStream bis = new BufferedInputStream(fis); BufferedOutputStream bos = new BufferedOutputStream(fos); int len =0 ; while ((len = bis.read()) != -1){ bos.write(len); } bos.close(); bis.close(); long endTime = System.currentTimeMillis(); System.out.println("文件复制共用了"+(endTime-startTime)+"毫秒"); } }
package iotest.bufferedIOtest.copytest; import java.io.*; //运用字节缓冲流,运用字节数组,来复制文件 //文件复制共用了10毫秒 public class Copy4 { public static void main(String[] args) throws IOException { long startTime = System.currentTimeMillis(); FileInputStream fis = new FileInputStream("C:\\test\\1.jpg"); FileOutputStream fos = new FileOutputStream("D:\\test\\1.jpg"); BufferedInputStream bis = new BufferedInputStream(fis); BufferedOutputStream bos = new BufferedOutputStream(fos); int len = 0; byte[] bytes = new byte[1024]; while ((len = bis.read(bytes)) != -1){ bos.write(bytes,0,len); } bos.close(); bis.close(); long endTime = System.currentTimeMillis(); System.out.println("文件复制共用了"+(endTime-startTime)+"毫秒"); } }
结论:数组+缓冲流 > 只用数组 > 只用缓冲流,来一个字节一个字节的读写 > 一个字节一个字节的读写
BufferedWriter类 extends Writer ---字符缓冲输出流
构造方法:
public BufferedWriter(Writer out) --默认缓冲数组
public BufferedWriter(Writer out, int sz)---size设置缓冲数组的大小
特有的方法:
public void newLine()---获取系统的换行符,写下来,换行(有这个方法不用区分系统换行符了)
package iotest.bufferedIOtest; import java.io.BufferedWriter; import java.io.FileWriter; import java.io.IOException; public class BufferedWriterTest01 { public static void main(String[] args) throws IOException { FileWriter fw = new FileWriter("src\\iotest\\bufferedIOtest\\a.txt"); BufferedWriter bw = new BufferedWriter(fw); bw.write("哈哈哈哈"); bw.newLine(); bw.write("喀斯柯达"); bw.close(); System.out.println(); } }
BufferedReader类extends Reader--字符缓冲输入流
构造方法:
public BufferedReader(Reader in)---默认缓冲数组
public BufferedReader(Reader in, int sz) ---size设置缓冲数组的大小
特有的方法:
public String readLine() ---读取一行数据
行的终止符号:可以是换行\n,回车\r,也可以是\r\n
返回值:
包含该行内容的字符串,不包含任何行终止符,如果到达流末尾,返回null
package iotest.bufferedIOtest; import java.io.BufferedReader; import java.io.FileReader; import java.io.IOException; public class BufferReaderTest01 { public static void main(String[] args) throws IOException { FileReader fr = new FileReader("src\\iotest\\bufferedIOtest\\a.txt"); BufferedReader br = new BufferedReader(fr); /*int len = 0; while ((len = br.read()) != -1){ System.out.println((char) len); }*/ String line = null; while ((line = br.readLine()) != null){ System.out.print(line); } br.close(); } }
练习:对文本内容进行排序
a.txt文本中
4.哈哈哈手机单
1.Adam什么的
3.爱迪生,啊啊大
2.啊看到了
6.asda,;阿克苏达
5.马上打多少吗
b.txt文本中
变成
1.Adam什么的
2.啊看到了
3.爱迪生,啊啊大
4.哈哈哈手机单
5.马上打多少吗
6.asda,;阿克苏达
package iotest.bufferedIOtest; import java.io.*; import java.util.HashMap; import java.util.Iterator; import java.util.Map; public class SortText { public static void main(String[] args) throws IOException { HashMap<Integer,String> hashMap = new HashMap<Integer, String>(); FileReader fr = new FileReader("src\\iotest\\bufferedIOtest\\a.txt"); FileWriter fw = new FileWriter("src\\iotest\\bufferedIOtest\\b.txt"); BufferedReader br = new BufferedReader(fr); BufferedWriter bw = new BufferedWriter(fw); //按行来读取文件 String line = null; while ((line = br.readLine()) != null){ //每行将string按.分割,存储到hashmap中,注意.为转义字符,需要用\\变为普通的. String[] split = line.split("\\."); hashMap.put(Integer.valueOf(split[0]),split[1]); } //对hashmap按key进行排序,hashmap会自动排好序,这儿为手动排序 /* Iterator iter = hashMap.entrySet().iterator(); while (iter.hasNext()) { Map.Entry entry = (Map.Entry) iter.next(); Object key = entry.getKey(); Object val = entry.getValue(); }*/ //按key遍历hashmap,将key和value拼接成完整的一行,写入文件中 for(Integer key:hashMap.keySet()){ bw.write(key+"."+hashMap.get(key)); bw.newLine();//换行 } bw.close(); br.close(); } }