java学习笔记一 2019.6.18 周二三亚特别热

悠悠 2022-01-11 04:59 198阅读 0赞

一、OutputStream write  
import java.io.File;  
import java.io.FileNotFoundException;  
import java.io.FileOutputStream;  
import java.io.IOException;  
import java.io.OutputStream;

public class StreamTest2 \{

public static void main(String[] args) {
        // TODO Auto-generated method stub
        //File file=new File("/Users/hanzhao/Desktop/zhaohanhan.txt");
        //System.out.println(file.exists());
    
        //题外话
        String s="aa我";
        System.out.println(s.length());//返回3个字符char
        byte[]bytes1=s.getBytes();
        System.out.println(bytes1.length);//返回5个字节，一个字母一个字节，一个汉字两个字节
    
        //FileOutputStream fos = null;//局部变量要赋值
        OutputStream fos = null;//用FileOutputStream 的父类来调用，OutputStream是abstract抽象类，不能new
        try {
    //  fos = new FileOutputStream("/Users/hanzhao/Desktop/zhaohanhan.txt");
        fos=new FileOutputStream("/Users/hanzhao/Desktop/daleilei.txt");
        byte[] bytes="aaa找找找adfsdfsdfads的房间都是法律框架上的六块腹肌都是".getBytes();//String类里面的方法，返回byte【】
        fos.write(bytes);
        //fos.close();//如果前面的代码出现问题，那么fos.close();就不会被执行，所以，把这个方法写在finally，保障一定被执行
        //不执行的话，会占用资源，执行一次占用一次
        }catch(FileNotFoundException e) {
            System.out.println("找不到文件");
        }catch(IOException ex) {
            System.out.println("找不到文件流");
        }finally {
            if(fos!=null) {
                try {
                fos.close();
                }catch(IOException e) {
                    //里面可以不写，耍流氓啊啊啊啊啊啊
                }
            }
        }  //结果就是daleilei.txt被写入内容
    
    }

二、InputStream read  
import java.io.FileInputStream;  
import java.io.FileNotFoundException;  
import java.io.IOException;  
import java.io.InputStream;

public class StreamTest1 \{

public static void main(String[] args) {
        // TODO Auto-generated method stub
        InputStream fis = null;
        try {
            fis = new FileInputStream("/Users/hanzhao/Desktop/xiaoshuo.txt");
            //xiaoshuo.txt里面已经放好了内容，把这些内容read到console控制台里面
            byte[] bytes = new byte[50];
            /*int b=fis.read(bytes);//返回值int，代表每次读的字节数
            System.out.println(b);//每次读50个字节
            System.out.println(bytes);//[B@79698539
            System.out.println(new String(bytes));
            //要把read的bytes字节转换为String数据,但是这样只能read到50个字节的内容，所有我们要用while循环以下
            */
            while(fis.read(bytes)>0) {//如果写成fis.read()>0，显示为一片空白
                String s=new String(bytes);
                System.out.print(s);
                System.out.println(s);
            }//read成功，但是有乱码，这是因为读取字节流，按每次50个字节读，有可能会read到半个汉字的原因。
    
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            System.out.println("文件地址不对");
            // e.printStackTrace();
        } catch (IOException e) {
            System.out.println("read❌");
        } finally {
            if (fis != null) {
                try {
                    fis.close();
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    // e.printStackTrace();
                }
            }
        }
    
    }

\}  
三、字节流，read and write  
// 没有调用IOUtils中的copy方法，老老实实自己写  
import java.io.FileInputStream;  
import java.io.FileNotFoundException;  
import java.io.FileOutputStream;  
import java.io.IOException;  
import java.io.InputStream;  
import java.io.OutputStream;

public class StreamTest3 \{

public static void main(String[] args) {
        // TODO Auto-generated method stub
        long startMS = System.currentTimeMillis();
        InputStream fis = null;
        OutputStream fos = null;
        try {
            fis = new FileInputStream("/Users/hanzhao/Desktop/zhaizhai.txt");
            fos = new FileOutputStream("/Users/hanzhao/Desktop/xiaofengfeng.txt");
            byte[] bytes = new byte[1204];
            int len;
            while ((len = fis.read(bytes)) > 0) {
                fos.write(bytes, 0, len);
            }
    
            long endMS = System.currentTimeMillis();
            System.out.println("copytime is" + (endMS - startMS));
    
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            // e.printStackTrace();
            System.out.println("file is not exist" + e.getMessage());
    
        } catch (IOException e) {
            // TODO Auto-generated catch block
            // e.printStackTrace();
            System.out.println();
        } finally {
            IOUtils.closeQuietly(fis);
            IOUtils.closeQuietly(fos);
        }
    
    }

四、调用了IOUtils中的方法了  
import java.io.FileInputStream;  
import java.io.FileNotFoundException;  
import java.io.FileOutputStream;  
import java.io.IOException;  
import java.io.InputStream;  
import java.io.OutputStream;

public class StreamTest5 \{

public static void main(String[] args) {
    
        //调用了IOUtils中的方法了
        long startMS = System.currentTimeMillis();
        InputStream fis = null;
        OutputStream fos = null;
        try {
            fis = new FileInputStream("/Users/hanzhao/Desktop/zhaizhai.txt");
            fos = new FileOutputStream("/Users/hanzhao/Desktop/xiaofengfeng.txt");
            /*byte[] bytes = new byte[1204];
            int len;
            while ((len = fis.read(bytes)) > 0) {
                fos.write(bytes, 0, len);
            }*/
            IOUtils.copy(fis, fos);
    
            long endMS = System.currentTimeMillis();
            System.out.println("copytime is" + (endMS - startMS));
    
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            // e.printStackTrace();
            System.out.println("file is not exist" + e.getMessage());
    
        } catch (IOException e) {
            // TODO Auto-generated catch block
            // e.printStackTrace();
            System.out.println();
        } finally {
            IOUtils.closeQuietly(fis);
            IOUtils.closeQuietly(fos);
        }
    
    }

//自己写的copy方法，好搞笑写的，太×××烂啦，怎么想的，int bufferSize明明指的是1024等等数值，我怎么把它想成返回值了  
//还有，公式不是万能的啊，明明只能代替下面这些，我怎么全写上了，服了，服了。。。。。。  
// byte\[\] bytes = new byte\[1204\];  
// int buffSize1;  
// while ((buffSize1 = inStream1.read(bytes)) > 0) \{  
// outStream1.write(bytes, 0, buffSize1);  
// \}  
//copy方法放在IUOtils类里面了，方便一些存放和调用  
public static void copy(InputStream inStream, OutputStream outStream, int bufferSize) \{

InputStream inStream1 = null;
        OutputStream outStream1 = null;
        try {
            inStream1 = new FileInputStream("/Users/hanzhao/Desktop/zhaizhai.txt");
            outStream1 = new FileOutputStream("/Users/hanzhao/Desktop/xiaofengfeng.txt");
            byte[] bytes = new byte[1204];
            int buffSize1;
            while ((buffSize1 = inStream1.read(bytes)) > 0) {
                outStream1.write(bytes, 0, buffSize1);
            }
    
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            // e.printStackTrace();
            System.out.println("file is not exist" + e.getMessage());
    
        } catch (IOException e) {
            // TODO Auto-generated catch block
            // e.printStackTrace();
            System.out.println();
        } finally {
            IOUtils.closeQuietly(inStream1);
            IOUtils.closeQuietly(outStream1);
        }
    
    }

五、IOUtils类，Utils意思为工具类，里面存放的全部是static静态方法  
import java.io.Closeable;  
import java.io.IOException;  
import java.io.InputStream;  
import java.io.OutputStream;  
import java.io.Reader;  
import java.io.Writer;

public class IOUtils \{

// IOUtils utils代表工具类，里面是static类
    // InputStream OutputStream Reader Writer都implements Closeable
    // 所以都可以调用close();方法，体现了不同对象的多态
    
    public static void closeQuietly(InputStream inStream) {
        if (inStream != null) {
            try {
                inStream.close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    }
    
    public static void closeQuietly(OutputStream outStream) {
        if (outStream != null) {
            try {
                outStream.close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    }
    
    public static void closeQuietly(Reader reader) {
        if (reader != null) {
            try {
                reader.close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    }
    
    public static void closeQuietly(Writer writer) {
        if (writer != null) {
            try {
                writer.close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    }
    
    public static void closeQuietly(Closeable closeable) {
        if (closeable != null) {
            try {
                closeable.close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    }
    
    public static void copy(InputStream inStream, OutputStream outStream, int bufferSize) throws IOException {
        // 程序要严谨，要判断inStream，outStream如果==null，bufferSize如果小于等于0，都要抛出异常
        if (inStream == null) {
            throw new IllegalArgumentException("inStream不能为空");
            // IllegalArgumentException extends RuntimeException   把异常抛出去 由调用着处理
        }
        if (outStream == null) {
            throw new IllegalArgumentException("outStream不能为空");
        }
        if (bufferSize <= 0) {
            throw new IllegalArgumentException("bufferSize不能为负数");
        }
        byte[] buffer = new byte[bufferSize];
        int len;
        while ((len = inStream.read(buffer)) > 0) {// 把异常抛出去 由调用着处理
            outStream.write(buffer, 0, len);
        }
    }
    
    public static void copy(InputStream inStream, OutputStream outStream) throws IOException{
        copy(inStream, outStream, 1024*1024);//把异常抛出去，由调用着处理
    }

六、自己写着实验用的IOUtils  
import java.io.Closeable;  
import java.io.IOException;

public class IOUtils2 implements Closeable \{

public IOUtils2() {
        super();
        // TODO Auto-generated constructor stub
    }
    
    @Override
    public void close() throws IOException {
        // TODO Auto-generated method stub
    
    }

七、自己写着实验用的IOUtils

import java.io.Closeable;  
import java.io.IOException;

public interface IOUtils3 extends Closeable\{

@Override
    default void close() throws IOException {
        // TODO Auto-generated method stub
    
    }

总结；要敢于犯错，在错误中总结经验。

转载于:https://blog.51cto.com/14394144/2410705