Java入门16

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d13

java.io.FileReader

• 1 核心类　sun.nio.cs.StreamDecoder
• 2 read() 读取一个字符串
• ３ read(char[ ]) 读取多个字符串

java.io.FileWriter

• 核心类　sun.nio.cs.StreamEncoder

缓冲区字符流

• １　BufferedReader
• 2 BufferedWriter
  

装饰模式

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1.实现方法

Buffered类继承Writer类，在类中添加Writer类型的成员变量，
对相应的方法进行重写，调用成员变量的方法进行完成

class BufferedWriter extends Writer{
	Writer out;
	char[ ] = new char[8192] ; 

	public void writer(String str){
	//先将数据写入缓冲区
	cb.xxx
	//如果cb已经满了，在写入到out中
}
public void close(){
	//1.清理cb
	//2.关闭out
}
	
}

设计思路
对原来方法进行一个包裹

public abstract class Writer implements Appendable, Closeable, Flushable {
    private char[] writeBuffer;
    private static final int WRITE_BUFFER_SIZE = 1024;
    protected Object lock;

    protected Writer() {
        this.lock = this;
    }

    protected Writer(Object var1) {
        if (var1 == null) {
            throw new NullPointerException();
        } else {
            this.lock = var1;
        }
    }

==========================================================

BufferedWriter

函数的回调

BufferedWriter 和 BufferedReader为带有默认缓冲的字符输出输入流，比没有缓冲区的效率高。
BufferedWriter

//构造方法
bufferedWriter bf  = new bufferedWriter(Writer out);
//主要方法
void writer(char ch );//写入单个字符
void writer(char [ ] cbuf, int off , int len)//写入字符数据的某一个部分
void writer(String s , int off , int len)//写入字符串的某一部分
void newLine()//写入一个行分隔符
void flush()//
void close()

================================================

import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.IOException;

public class BufferedWriterDemo {
    public static void main(String[] args)throws IOException {
        FileWriter fw = new FileWriter("/media/ifeng/_dde_data/iotest/hello2.txt");
        /*创建一个字符写入流的缓冲区对象，并和指定的要被缓冲的流对象想关联*/
        BufferedWriter bufw = new BufferedWriter(fw);

        //使用缓冲区的方法将数据写入到缓冲区中
        bufw.write("hello world!");
        bufw.newLine();
        bufw.newLine();
        bufw.write("hello world!2");
        bufw.write("hello world!3");

        bufw.close();

    }
}

BufferedReader

构造方法

BufferedReader br = new BufferReader(Reader in);

主要方法

int read( );//读取单个字符
int read(char[ ] ,int off,int len);//将字符读入到数组的某一个部分，返回读取的字符数，达到尾部，返回-1
String readLine( ); //读取一个文本行
void close( ); //

import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;

public class BufferedReaderDemo {
    private FileReader fr;
    private char []buf = new char[1024];
    private int count = 0;
    private int pos = 0;
    public BufferedReaderDemo(FileReader f){
        this.fr = f;
    }
    public int myRead() throws IOException{
        if(count == 0){
            count = fr.read(buf);
            pos = 0;
        }
        if(count < 0 ){
            return -1;
        }
        int ch = buf[pos++];
        count--;
        return ch;
    }

    public String myReadLine() throws IOException{
        StringBuilder sb = new StringBuilder();
        int ch = 0;
        while ((ch = myRead())!= -1){
            if(ch == '\r')
                continue;
            if(ch == '\n')
                return sb.toString();
            sb.append((char) ch);
            if(count == 0)
                return sb.toString();

        }
        return null;
    }
}

复制文本的小程序

BufferedReaderDemo.java

import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;

public class BufferedReaderDemo {
    private FileReader fr;
    private char []buf = new char[1024];
    private int count = 0;
    private int pos = 0;
    public BufferedReaderDemo(FileReader f){
        this.fr = f;
    }
    public int myRead() throws IOException{
        if(count == 0){
            count = fr.read(buf);
            pos = 0;
        }
        if(count < 0 ){
            return -1;
        }
        int ch = buf[pos++];
        count--;
        return ch;
    }

    public String myReadLine() throws IOException{
        StringBuilder sb = new StringBuilder();
        int ch = 0;
        while ((ch = myRead())!= -1){
            if(ch == '\r')
                continue;
            if(ch == '\n')
                return sb.toString();
            sb.append((char) ch);
            if(count == 0)
                return sb.toString();

        }
        return null;
    }
}

BufferedWriterDemo.java

import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.IOException;

public class BufferedWriterDemo {
    public static void main(String[] args)throws IOException {
        FileWriter fw = new FileWriter("/media/ifeng/_dde_data/iotest/hello2.txt");
        /*创建一个字符写入流的缓冲区对象，并和指定的要被缓冲的流对象想关联*/
        BufferedWriter bufw = new BufferedWriter(fw);

        //使用缓冲区的方法将数据写入到缓冲区中
        bufw.write("hello world!");
        bufw.newLine();
        bufw.newLine();
        bufw.write("hello world!2");
        bufw.write("hello world!3");

        bufw.close();

    }
}

TextCopyByBuf.java

import java.io.*;

public class TextCopyByBuf {
    public static void main(String[] args) throws IOException {
        FileReader fr = new FileReader("/media/ifeng/_dde_data/iotest/hello2.txt");
        FileWriter fw = new FileWriter("/media/ifeng/_dde_data/iotest/hello3.txt");
        BufferedReader bufr = new BufferedReader(fr);
        BufferedWriter bufw = new BufferedWriter(fw);

        //一行一行的写入
        String line = null;
        while ((line = bufr.readLine())!=null){
            bufw.write(line);
            bufw.newLine();
            bufw.flush();

        }
/*        //一个字节一个字节的写入
        int ch = 0;
        while ((ch = bufr.read())! = -1){
            bufw.write(ch);
        }*/
        bufr.close();
        bufw.close();
    }
}

字节流

• 基本操作和字符流相同
• 不仅可以操作字符，还可以操作其他媒体文件

===========================================

Junit 单元测试在 intelliJ IDEA 中的应用

ps:单元测试可以没有main运行

===========================================

---

Copy一个jpg文件

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.FileWriter;

public class ByteStreamDemo {
    /*
    *
    * 使用字节流复制图片
    */
    public void main() throws Exception{
        //文件输入流（字节流）
        FileInputStream fin = new FileInputStream("/media/ifeng/_dde_data/iotest/1.jpg");
        //文件输出流
        FileOutputStream fout = new FileOutputStream("/media/ifeng/_dde_data/iotest/qinfang.jpg");

        byte [ ] buffer = new byte[1024];
        int len = -1 ;
        System.out.println("1111111");
        while (((len = fin.read(buffer)) != -1)){
            fout.write(buffer,0,len);
        }
        fin.close();
        fout.close();
        System.out.println("over");
    }
}

================================
使用文件输入流读取文本文件

import java.io.FileOutputStream;

public class ByteStreamDemo2 {
    public static void main(String[] args) throws Exception {
        System.out.println(charset.defaultCharset());
        String str = "你好中国人";
        FileOutputStream fos =  new FileOutputStream("/media/ifeng/_dde_data/iotest/text222.txt");
        fos.write(str.getBytes());
        fos.close();
        System.out.println("over!");
    }
}

==========================================
字节流

---

1.FileInputStream

支持skip()方法，skip向后跳的时候不能文件头地址，可以超过文件末尾地址

2.FileOutputStream

不支持skip

RandomAccessFile

随机访问文件，定位到文件的任意位置