摘要：虛擬機讀取其他進(jìn)程的數(shù)據(jù)對象的方法可以運行平臺上的其他程序該方法產(chǎn)生一個對象對象代表由該程序啟動啟動的子進(jìn)程類提供如下三個方法用于和其子進(jìn)程通信獲取子進(jìn)程的錯誤流獲取子進(jìn)程的輸入流獲取子進(jìn)程的輸出流這里的輸入流輸出流容易混淆從程序的角度思考

Runtime對象的exec方法可以運行平臺上的其他程序,該方法產(chǎn)生一個Process對象,Process對象代表由該Java程序啟動啟動的子進(jìn)程,Process類提供如下三個方法,用于和其子進(jìn)程通信:

InputStream getErrorStream() 獲取子進(jìn)程的錯誤流
InputStream getInputStream() 獲取子進(jìn)程的輸入流
OutputStream getOutputStream() 獲取子進(jìn)程的輸出流

  
這里的輸入流輸出流容易混淆.從程序的角度思考,子進(jìn)程讀取程序的數(shù)據(jù),為輸出流.子進(jìn)程讀取數(shù)據(jù),是讓程序把數(shù)據(jù)輸出到子進(jìn)程中.

java//省略代碼

            Process p = Runtime.getRuntime().exec("javac");
            BufferedReader br = new BufferedReader(new InputStreamReader(p.getErrorStream(),"GBK"));
            String buff;
            while ((buff = br.readLine()) != null ) {
                System.out.println(buff);
            }

//省略代碼

javapublic class WriteToProcess {
    public static void main(String[] args) {
        PrintStream ps = null;
        try {
            //返回運行該命令的子進(jìn)程
            Process p = Runtime.getRuntime().exec("java ReadStand");
            //p進(jìn)程的輸出流創(chuàng)建PrintStream對象
            //對本程序是輸出流,對p進(jìn)程則是輸入流
            ps = new PrintStream(p.getOutputStream());
            BufferedReader br = new BufferedReader(new InputStreamReader(p.getInputStream()));
            String content;
            while ((content = br.readLine()) != null) {
                System.out.println(content);
            }
            ps.println("普通字符串");
            ps.println(new WriteToProcess());
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } finally {
            if (null != ps) {
                ps.close();
            }
        }
    }
}
class ReadStand {
    public static void main(String[] args) {
        PrintStream ps = null;
        Scanner sc = new Scanner(System.in);
        try {
            ps = new PrintStream("src	estout.txt");
            sc.useDelimiter("
");
            while (sc.hasNext()) {
                ps.print("鍵盤輸入的內(nèi)容是:" + sc.next());
            }
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } finally {
            sc.close();
            ps.close();
        }
    }
}

  
計算機中"隨機訪問"是由Random Access兩個單詞單詞翻譯而來.Random不僅有隨機的意思,還有任意的意思.如果

  能這樣理解Random,可以更好的理解Random Access:任意訪問,也就是說可以自由訪問任意存儲點的存儲器(與磁盤,

  磁帶等需要尋道,倒帶才可訪問存儲點的存儲器區(qū)分);而RandomAccessFile的含義是可以自由訪問文件的任意地方(與

  InputStream,Reader依次向后讀取區(qū)分).

    //省略代碼
    RandomAccessFile raf = null;
    //省略代碼
    try {
        raf = new RandomAccessFile("out.txt","rw");
        raf.seek(raf.length());
        raf.write("追加內(nèi)容
".getBytes());
    }

javapublic static void insert(String fileName,long pos,String insertContent) {
        RandomAccessFile raf = null;
        try {
            raf = new RandomAccessFile(fileName, "rw");
            File tmpFile = File.createTempFile("temp", null);
            tmpFile.deleteOnExit();
            BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(tmpFile)));
            BufferedReader br = new BufferedReader(new InputStreamReader(new FileInputStream(tmpFile)));
            //設(shè)置文件指針位置
            raf.seek(pos);
            String content;
            /**
             * 將插入點內(nèi)容保存在臨時文件中
             * 讀取插入點后所有文件內(nèi)容
             */
            while ((content = raf.readLine()) != null) {
                    //將數(shù)據(jù)寫入臨時文件
                    bw.write(content);
            }
            bw.flush();
            bw.close();
            //重新設(shè)置指針位置
            raf.seek(pos);
            //插入內(nèi)容
            raf.write(insertContent.getBytes());
            //追加臨時文件中內(nèi)容
            while ((content = br.readLine()) != null) {
                raf.write(content.getBytes());
            }
            br.close();
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } finally {
            try {
                raf.close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }


    }

javapublic class ObjectOutputStreamTest {
    public static void main(String[] args) {
        ObjectOutputStream oos = null;

        try {
            //創(chuàng)建一個ObjectOutputStream輸出流
            oos = new ObjectOutputStream(new FileOutputStream("src//io//person.txt"));
            Person p1 = new Person("swk", 20);
            //把對象寫入輸出流
            oos.writeObject(p1);
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } finally { 
                try {
                    if (null != oos) {
                        oos.close();
                    }
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
        }
    }

class Person implements Serializable {

    private static final long serialVersionUID = 1L;
    private String name;
    private int age;

    public Person(String name,int age) {
        // TODO Auto-generated constructor stub    
        System.out.println("Person 構(gòu)造函數(shù)");
        this.name = name;
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }


}

java//省略代碼
    ObjectInputStream ois = null;
        try {
            //創(chuàng)建ObjectInputStream輸入流
            ois = new ObjectInputStream(new FileInputStream("src//io//person.txt"));
            //從流中讀取對象,并強制轉(zhuǎn)換為Person類型
            Person p = (Person)ois.readObject();
            System.out.println("Age:" + p.getAge() + ",name:" + p.getName());
        } 
//省略代碼

  
反序列化讀取的只是Java對象的數(shù)據(jù),而不是Java類,因此采用反序列化恢復(fù)Java對象時,必須提供Java對象所屬的class文件,否則引發(fā)ClassNotFoundException.

  
Person類只有一個有參數(shù)構(gòu)造器,并沒有無參數(shù)構(gòu)造器,而且構(gòu)造函數(shù)內(nèi)有打印語句.當(dāng)反序列化讀取Java對象時,沒有看到程序調(diào)用該構(gòu)造器,這表明反序列化機制無需通過構(gòu)造器來初始化Java對象.

  
如果向文件中使用序列化多個Java對象,使用反序列化機制恢復(fù)時,必須按實際寫入順序讀取.