Java-Grundlagen – iO (3)

一、管道流

演示：PipedInputStream  , PipedOutputStream

注意：管道流本身就不建议在一个线程中使用，这是因为向输出流中写的数据，都会存到输入流内部的一个1024字节大小的数组中，如果写的内容超过这个数组的大小，而且没有被输入流读取的话，输出流所在的线程就会等待，如果这时是在同一个线程中，该线程就会死锁，不推荐在同一个线程中使用。（API）

<span style="color: #0000ff">import</span><span style="color: #000000"> java.io.IOException;
</span><span style="color: #0000ff">import</span><span style="color: #000000"> java.io.PipedInputStream;
</span><span style="color: #0000ff">import</span><span style="color: #000000"> java.io.PipedOutputStream;

</span><span style="color: #0000ff">public</span> <span style="color: #0000ff">class</span><span style="color: #000000"> Test17 {
    </span><span style="color: #0000ff">public</span> <span style="color: #0000ff">static</span> <span style="color: #0000ff">void</span> main(String[] args) <span style="color: #0000ff">throws</span><span style="color: #000000"> IOException,
            InterruptedException {
        Sender sender </span>= <span style="color: #0000ff">new</span><span style="color: #000000"> Sender();
        Receiver receiver </span>= <span style="color: #0000ff">new</span><span style="color: #000000"> Receiver();

        PipedOutputStream out </span>=<span style="color: #000000"> sender.getOut();
        PipedInputStream in </span>=<span style="color: #000000"> receiver.getIn();

        in.connect(out);
        </span><span style="color: #008000">//</span><span style="color: #008000"> out.connect(in); </span><span style="color: #008000">//</span><span style="color: #008000">这样也可以</span>
<span style="color: #000000">
        sender.start();

        Thread.sleep(</span>10<span style="color: #000000">);
        receiver.start();
    }
}

</span><span style="color: #008000">//</span><span style="color: #008000"> 发送者</span>
<span style="color: #0000ff">class</span> Sender <span style="color: #0000ff">extends</span><span style="color: #000000"> Thread {
    </span><span style="color: #0000ff">private</span> PipedOutputStream out = <span style="color: #0000ff">new</span><span style="color: #000000"> PipedOutputStream();

    </span><span style="color: #0000ff">public</span> <span style="color: #0000ff">void</span><span style="color: #000000"> run() {
        </span><span style="color: #0000ff">try</span><span style="color: #000000"> {
            </span><span style="color: #0000ff">int</span> i = 1<span style="color: #000000">;
            </span><span style="color: #0000ff">while</span> (<span style="color: #0000ff">true</span><span style="color: #000000">) {
                Thread.sleep(</span>2000<span style="color: #000000">);
                String msg </span>= "你好,这是发送端发的第" + i++ + "条信息"<span style="color: #000000">;
                out.write(msg.getBytes());
            }
        } </span><span style="color: #0000ff">catch</span><span style="color: #000000"> (Exception ex) {
            ex.printStackTrace();
        }
    }

    </span><span style="color: #0000ff">public</span><span style="color: #000000"> PipedOutputStream getOut() {
        </span><span style="color: #0000ff">return</span> <span style="color: #0000ff">this</span><span style="color: #000000">.out;
    }
}

</span><span style="color: #008000">//</span><span style="color: #008000"> 接收者</span>
<span style="color: #0000ff">class</span> Receiver <span style="color: #0000ff">extends</span><span style="color: #000000"> Thread {
    </span><span style="color: #0000ff">private</span> PipedInputStream in = <span style="color: #0000ff">new</span><span style="color: #000000"> PipedInputStream();

    </span><span style="color: #0000ff">public</span> <span style="color: #0000ff">void</span><span style="color: #000000"> run() {
        </span><span style="color: #0000ff">try</span><span style="color: #000000"> {
            </span><span style="color: #0000ff">while</span> (<span style="color: #0000ff">true</span><span style="color: #000000">) {
                </span><span style="color: #0000ff">byte</span>[] buff = <span style="color: #0000ff">new</span> <span style="color: #0000ff">byte</span>[1024<span style="color: #000000">];
                </span><span style="color: #0000ff">int</span> len =<span style="color: #000000"> in.read(buff);
                String str </span>= <span style="color: #0000ff">new</span> String(buff, 0<span style="color: #000000">, len);
                System.out.println(str);
            }
        } </span><span style="color: #0000ff">catch</span><span style="color: #000000"> (Exception ex) {
            ex.printStackTrace();
        }
    }

    </span><span style="color: #0000ff">public</span><span style="color: #000000"> PipedInputStream getIn() {
        </span><span style="color: #0000ff">return</span> <span style="color: #0000ff">this</span><span style="color: #000000">.in;
    }
}

</span><span style="color: #008000">//</span><span style="color: #008000"> Pipe closed 发生在管道关了,发送者还在发的情况下</span>

二、文件切割和合并

<span style="color: #0000ff">public</span> <span style="color: #0000ff">static</span> <span style="color: #0000ff">void</span> merget2() <span style="color: #0000ff">throws</span><span style="color: #000000"> Exception {
        OutputStream out</span>=<span style="color: #0000ff">new</span> FileOutputStream("c:/src_new.zip"<span style="color: #000000">);
        BufferedOutputStream bos</span>=<span style="color: #0000ff">new</span><span style="color: #000000"> BufferedOutputStream(out);
        
        </span><span style="color: #0000ff">for</span>(<span style="color: #0000ff">int</span> i=1;i<=20;i++<span style="color: #000000">){
            InputStream in</span>=<span style="color: #0000ff">new</span> FileInputStream("c:/src_"+<span style="color: #000000">i);
            </span><span style="color: #0000ff">byte</span> [] buff=<span style="color: #0000ff">new</span> <span style="color: #0000ff">byte</span><span style="color: #000000">[in.available()];    
            in.read(buff);
            bos.write(buff);    
            in.close();    
        }
        
        bos.close();
        
        System.out.println(</span>"合并成功"<span style="color: #000000">);
    }
    
    
    </span><span style="color: #0000ff">public</span> <span style="color: #0000ff">static</span> <span style="color: #0000ff">void</span> merge()<span style="color: #0000ff">throws</span><span style="color: #000000"> Exception{
        OutputStream out</span>=<span style="color: #0000ff">new</span> FileOutputStream("c:/src_new.zip"<span style="color: #000000">);
        </span><span style="color: #0000ff">for</span>(<span style="color: #0000ff">int</span> i=1;i<=20;i++<span style="color: #000000">){
            
            InputStream in</span>=<span style="color: #0000ff">new</span> FileInputStream("c:/src_"+<span style="color: #000000">i);
            
            </span><span style="color: #0000ff">byte</span> [] buff=<span style="color: #0000ff">new</span> <span style="color: #0000ff">byte</span><span style="color: #000000">[in.available()];
            
            in.read(buff);
            out.write(buff);
            
            in.close();
            
        }
        
        out.close();
        
        System.out.println(</span>"合并成功"<span style="color: #000000">);
    }</span>

四、File 类概述

流只能操作数据

File 类 是IO包中,唯一代表磁盘文件本身的类

File 定义了一些与平台无关的方法来操作文件

File: 文件和目录路径名的抽象表示形式。//路径也是一种文件

用来将文件或文件夹封装成对象

方便对文件及文件夹的属性信息进行操作

File对象.经常做为参数传给流的构造函数

File类不能访问文件内容,即不能从文件中读数据,也不能写入数据,它只能对文件本身的属性进行操作

五、File 类的常见操作

boolean createNewFile() //创建一个新文件,成功返回true ,否则返回false ,如果文件已经存在,则返回false,和流不一样,流是覆盖

mikdir()  mikdirs  //创建目录,后者可以创建多级目录

boolean delete ()  //删除 删除此抽象路径名表示的文件或目录。如果此路径名表示一个目录，则该目录必须为空才能删除。 否则返回false

void deleteOnExit() //在虚拟机终止时,删除文件或目录 注意它的返回类型是void 因为虚拟机都终止了,当然要返回值也没用了

exists() // 测试此抽象路径名表示的文件或目录是否存在。

isDirectory() // 判断是否是目录

isFile() //判断是否是文件

isHidden() //判断是否是隐藏文件

<span style="color: #0000ff">static</span> <span style="color: #0000ff">void</span> fileDemo() <span style="color: #0000ff">throws</span><span style="color: #000000"> IOException{
        File f1</span>=<span style="color: #0000ff">new</span> File("1.txt"); <span style="color: #008000">//</span><span style="color: #008000">当前路径下</span>
        File f2=<span style="color: #0000ff">new</span> File("c:\\2.txt"<span style="color: #000000">);
        File f3</span>=<span style="color: #0000ff">new</span> File("c:\\","3.txt"<span style="color: #000000">);
        File f4</span>=<span style="color: #0000ff">new</span> File("c:\\"<span style="color: #000000">);
        File f5</span>=<span style="color: #0000ff">new</span> File(f4,"5.txt");  <span style="color: #008000">//</span><span style="color: #008000">File(File parent,String child)</span>
        
        <span style="color: #008000">/*</span><span style="color: #008000">f1.createNewFile();
        f2.createNewFile();
        f3.createNewFile();
        System.out.println(f4.createNewFile());    //返回false
        f5.createNewFile();
</span><span style="color: #008000">*/</span>        
    <span style="color: #008000">/*</span><span style="color: #008000">    System.out.println(f1.delete());  //true
        System.out.println(f2.delete());  //true
        System.out.println(f3.delete());  //true
        System.out.println(f4.delete());  //false
        System.out.println(f5.delete());  //true
        </span><span style="color: #008000">*/</span>
        
        <span style="color: #008000">//</span><span style="color: #008000">System.out.println(    new File("c:/aaa").delete()); </span><span style="color: #008000">//</span><span style="color: #008000">(aaa是个文件夹)如果aaa下有内容,则返回false,否则返回true,并将文件夹删除</span>
        
    <span style="color: #008000">/*</span><span style="color: #008000">    File f=new File("c:\\BBBSSS\\1.txt\\cc\\dd");  //这样写,1.txt也会被做为文件夹的名称
        f.mkdirs();  //创建多级的时候,用mkdirs();
        
        new File("c:/forlder1").mkdir();  //只能创建一级目录
     </span><span style="color: #008000">*/</span>        
        
        <span style="color: #008000">/*</span><span style="color: #008000">File ff=new File("c:\\不存在的文件.txt");
        System.out.println(ff.isDirectory()); //false
        System.out.println(ff.isFile()); //false
        System.out.println(ff.isHidden()); //false
        </span><span style="color: #008000">*/</span>        
    <span style="color: #008000">/*</span><span style="color: #008000">    
        File ff=new File("c:\\不存在的文件.txt");
        ff.createNewFile();
        System.out.println(ff.isDirectory()); //false
        System.out.println(ff.isFile());  //true
        System.out.println(ff.isHidden()); //false
   </span><span style="color: #008000">*/</span><span style="color: #000000">    
        
        File ff</span>=<span style="color: #0000ff">new</span> File("c:\\不存在的文件.txt"<span style="color: #000000">);
        ff.mkdir();
        System.out.println(ff.isDirectory()); </span><span style="color: #008000">//</span><span style="color: #008000">true</span>
        System.out.println(ff.isFile());  <span style="color: #008000">//</span><span style="color: #008000">false</span>
        System.out.println(ff.isHidden()); <span style="color: #008000">//</span><span style="color: #008000">false
        
        </span><span style="color: #008000">//</span><span style="color: #008000">注意,对于还没有创建的文件,或文件夹,isDirectory,isFile 都会返回false 要想得到正确结果,必须先用 exists判断    </span>
<span style="color: #000000">        
    }</span>

六、File 类获取文件信息类操作

String getName(); //返回文件或目录的名称

String getParent(); //返回父目录的名字,没有则返回null

String getPath(); //返回路径字串 ??? 含文件名

String getAbsolutePath(); // 返回绝对路径名字符串

//File getAbsoluteFile(); //返回绝对路径名形式。等同于 new File(this.getAbsolutePath())

long length(); //返回文件长度,以字节为单位

static File[] listRoots() //列出可用的文件系统根 在windows下即列出C D E等盘符

String [] list()  //返回目录中的文件和目录 (即连文件名一起返回)(隐藏文件也会被返回)

String [] list(FilenameFilter filter) //返回经过指定过滤器过滤的文件和目录。

File [] listFiles() //返回当前目录下所有的文件

File[] listFiles(FilenameFilter filter)

<span style="color: #0000ff">public</span> <span style="color: #0000ff">static</span> <span style="color: #0000ff">void</span><span style="color: #000000"> fileInfoDemo(){    
                File f</span>=<span style="color: #0000ff">new</span> File("c:\\Test\\1.txt"<span style="color: #000000">);
                System.out.println(</span>"getName--"+f.getName()); <span style="color: #008000">//</span><span style="color: #008000">1.txt</span>
                System.out.println("getParent()--"+f.getParent()); <span style="color: #008000">//</span><span style="color: #008000">c:\Test</span>
                System.out.println("getPath()--"+f.getPath()); <span style="color: #008000">//</span><span style="color: #008000">c:\Test\1.txt</span>
                System.out.println("getAbsolutePath--"+f.getAbsolutePath()); <span style="color: #008000">//</span><span style="color: #008000">c:\Test\1.txt</span>
                System.out.println("length()--"+f.length()); <span style="color: #008000">//</span><span style="color: #008000">1234</span>
<span style="color: #000000">                
               File[] fileList</span>=<span style="color: #000000">File.listRoots();
               </span><span style="color: #0000ff">for</span><span style="color: #000000">(File file : fileList)  {     
                       System.out.println (file); </span><span style="color: #008000">//</span><span style="color: #008000">打印出 C:\  D:\ 等</span>
<span style="color: #000000">               }
            }
</span>

 如果把上面的文件路径换成     File f=<span style="color: #0000ff">new</span> File("1.txt"); <span style="color: #008000">//</span><span style="color: #008000">使用的是相对路径,则结果为:</span>
                getName--1<span style="color: #000000">.txt
                getParent()</span>--<span style="color: #0000ff">null</span><span style="color: #000000">
                getPath()</span>--1<span style="color: #000000">.txt
                getAbsolutePath</span>--C:\workspace\Lession21\1<span style="color: #000000">.txt
                length()</span>--0<span style="color: #000000">
                A:\
                C:\
                D:\
                E:\</span>

<span style="color: #008000">//</span><span style="color: #008000">例 显示全部</span>
    <span style="color: #0000ff">static</span> <span style="color: #0000ff">void</span><span style="color: #000000"> listDemo(){
    File f</span>=<span style="color: #0000ff">new</span> File("C:/文件夹A/大学毕业论文收集"<span style="color: #000000">);
    String [] nameList</span>=<span style="color: #000000">f.list();
        </span><span style="color: #0000ff">for</span><span style="color: #000000">(String str:nameList){
        System.out.println(str);
    }    
}</span>

<span style="color: #008000">//</span><span style="color: #008000">例子,带过滤的</span>
    <span style="color: #0000ff">static</span> <span style="color: #0000ff">void</span><span style="color: #000000"> filterDemo(){
        File f</span>=<span style="color: #0000ff">new</span> File("C:/文件夹A/大学毕业论文收集/中文系"<span style="color: #000000">);
        File [] fileList</span>=f.listFiles(<span style="color: #0000ff">new</span><span style="color: #000000"> FilenameFilter() {
    </span><span style="color: #0000ff">public</span> <span style="color: #0000ff">boolean</span><span style="color: #000000"> accept(File dir, String name) {
        </span><span style="color: #0000ff">return</span> !name.endsWith(".exe"); <span style="color: #008000">//</span><span style="color: #008000">只看exe文件</span>
<span style="color: #000000">        }
        });
        </span><span style="color: #0000ff">for</span><span style="color: #000000"> (File item: fileList) {
        System.out.println(item.getName());
        }
}</span>

七、递归操作
递归的查看目录中的内容

<span style="color: #0000ff">public</span> <span style="color: #0000ff">static</span> <span style="color: #0000ff">void</span><span style="color: #000000"> main(String[] args) {
    recuDir(</span><span style="color: #0000ff">new</span> File("C:\\作业\\8.13"<span style="color: #000000">));
}
            
    </span><span style="color: #0000ff">static</span> <span style="color: #0000ff">void</span><span style="color: #000000"> recuDir(File dir){
    System.out.println(</span>"------------------"<span style="color: #000000">);
    File [] fileList</span>=<span style="color: #000000"> dir.listFiles();
                
    </span><span style="color: #0000ff">for</span><span style="color: #000000">(File f:fileList){
        </span><span style="color: #0000ff">if</span><span style="color: #000000">(f.isDirectory()){
        recuDir(f);  </span><span style="color: #008000">//</span><span style="color: #008000">递归调用</span>
        }<span style="color: #0000ff">else</span><span style="color: #000000">{
        System.out.println(f.getName());
        }
    }
}</span>

八、RandomAccessFile

java 语言中功能最丰富的文件访问类

支持 "随机访问" 方式

可以跳转到文件的任意位置读写数据

该类对象有个指示器,指向当前读写的位置,当读写n个字节后,文件指示器将指向这n个字节的下一个字节处

刚打开文件的时候,指示器指向指向文件开头,可以移动指示器到新的位置

在等长记录格式文件的随机读取时有极大优势,但它只限于操作文件,不能访问其他io设备,如网络,内存映像等

RandomAccessFile的构造函数

new RandomAccessFile(f,"rw");  //读写方式 (如果文件不存在,会创建)

new RandomAccessFile(f,"r");    //只读方式

<span style="color: #0000ff">public</span> <span style="color: #0000ff">static</span> <span style="color: #0000ff">void</span> main(String[] args) <span style="color: #0000ff">throws</span><span style="color: #000000"> IOException {
                </span><span style="color: #0000ff">final</span> <span style="color: #0000ff">int</span> LEN=8<span style="color: #000000">;
                </span><span style="color: #008000">/*</span><span style="color: #008000">Student stu1=new Student(20,"cat");
                Student stu2=new Student(21,"sheep");
                Student stu3=new Student(15,"duck");
                
                RandomAccessFile r=new RandomAccessFile("c:/stu.txt","rw");
                
                r.write(stu1.name.getBytes());
                r.writeInt(stu1.age);
                
                r.write(stu2.name.getBytes());
                r.writeInt(stu2.age);
                
                r.write(stu3.name.getBytes());
                r.writeInt(stu3.age);
                
                r.close();</span><span style="color: #008000">*/</span><span style="color: #000000">
                
                RandomAccessFile read</span>=<span style="color: #0000ff">new</span> RandomAccessFile("c:/stu.txt","rw"<span style="color: #000000">);
                
                read.skipBytes(</span>12);  <span style="color: #008000">//</span><span style="color: #008000">跳过第一个学生的信息,其中年龄是4个字节,姓名是8个字节</span>
                System.out.println("第二个学生的信息:"<span style="color: #000000">);
                    
                String str</span>=""<span style="color: #000000">;
                </span><span style="color: #0000ff">for</span>(<span style="color: #0000ff">int</span> i=0;i<LEN;i++<span style="color: #000000">){
                    str</span>+=(<span style="color: #0000ff">char</span><span style="color: #000000">)read.readByte();
                }
                System.out.println(</span>"name:"+<span style="color: #000000">str);
                System.out.println(</span>"age:"+<span style="color: #000000">read.readInt());
                
                System.out.println(</span>"第一个学生的信息:"<span style="color: #000000">);
                read.seek(</span>0<span style="color: #000000">);
                str</span>=""<span style="color: #000000">;
                </span><span style="color: #0000ff">for</span>(<span style="color: #0000ff">int</span> i=0;i<LEN;i++<span style="color: #000000">){
                    str</span>+=(<span style="color: #0000ff">char</span><span style="color: #000000">)read.readByte();
                }
                System.out.println(</span>"name:"+<span style="color: #000000">str);
                System.out.println(</span>"age:"+<span style="color: #000000">read.readInt());
                
                System.out.println(</span>"第三个学生的信息:"<span style="color: #000000">);
                read.skipBytes(</span>12<span style="color: #000000">);
                str</span>=""<span style="color: #000000">;
                </span><span style="color: #0000ff">for</span>(<span style="color: #0000ff">int</span> i=0;i<LEN;i++<span style="color: #000000">){
                    str</span>+=(<span style="color: #0000ff">char</span><span style="color: #000000">)read.readByte();
                }
                System.out.println(</span>"name:"+<span style="color: #000000">str);
                System.out.println(</span>"age:"+<span style="color: #000000">read.readInt());
                
                read.close();
        
            }</span>

九、Properties 类详解

Properties是 HashTable 的子类，它增加了将键和值保存到流中,或从流中读取的功能。如果要用 properties.store()方法存储其对象内容,则关键字和值必须是String型。可以从流中载入键值对信息 void load(InputStream inStream) 从输入流中读取属性列表（键和元素对）。
Set stringPropertyNames() 返回此属性列表中的键集。
注意：尽量不要用中文

<span style="color: #0000ff">public</span> <span style="color: #0000ff">static</span> <span style="color: #0000ff">void</span> main(String[] args) <span style="color: #0000ff">throws</span><span style="color: #000000">  IOException {
            Properties settings </span>=<span style="color: #0000ff">new</span><span style="color: #000000"> Properties();
            settings.load(</span><span style="color: #0000ff">new</span> FileInputStream("c:/config.ini"<span style="color: #000000">));
            
            System.out.println(settings.getProperty(</span>"port"));  <span style="color: #008000">//</span><span style="color: #008000">8080
                
            </span><span style="color: #008000">//</span><span style="color: #008000">从流中取</span>
            Set<String> set=settings.stringPropertyNames(); <span style="color: #008000">//</span><span style="color: #008000">取所有属性</span>
            <span style="color: #0000ff">for</span><span style="color: #000000">(String key:set){
                System.out.println(key</span>+":"+<span style="color: #000000">settings.getProperty(key));
            }
            
            </span><span style="color: #008000">//</span><span style="color: #008000">输入</span>
            settings.setProperty("niceCat", "this is a niceCat"<span style="color: #000000">); 
            settings.store(</span><span style="color: #0000ff">new</span> FileOutputStream("c:/config.ini"),"this is note"<span style="color: #000000">);
            
            System.out.println(</span>"ok"<span style="color: #000000">);
            
        }</span>