摘要：虛擬機讀取其他進程的數據對象的方法可以運行平臺上的其他程序該方法產生一個對象對象代表由該程序啟動啟動的子進程類提供如下三個方法用于和其子進程通信獲取子進程的錯誤流獲取子進程的輸入流獲取子進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,該方法產生一個Process對象,Process對象代表由該Java程序啟動啟動的子進程,Process類提供如下三個方法,用于和其子進程通信:

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

  
這里的輸入流輸出流容易混淆.從程序的角度思考,子進程讀取程序的數據,為輸出流.子進程讀取數據,是讓程序把數據輸出到子進程中.

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程
            Process p = Runtime.getRuntime().exec("java ReadStand");
            //p進程的輸出流創建PrintStream對象
            //對本程序是輸出流,對p進程則是輸入流
            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)));
            //設置文件指針位置
            raf.seek(pos);
            String content;
            /**
             * 將插入點內容保存在臨時文件中
             * 讀取插入點后所有文件內容
             */
            while ((content = raf.readLine()) != null) {
                    //將數據寫入臨時文件
                    bw.write(content);
            }
            bw.flush();
            bw.close();
            //重新設置指針位置
            raf.seek(pos);
            //插入內容
            raf.write(insertContent.getBytes());
            //追加臨時文件中內容
            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 構造函數");
        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對象的數據,而不是Java類,因此采用反序列化恢復Java對象時,必須提供Java對象所屬的class文件,否則引發ClassNotFoundException.

  
Person類只有一個有參數構造器,并沒有無參數構造器,而且構造函數內有打印語句.當反序列化讀取Java對象時,沒有看到程序調用該構造器,這表明反序列化機制無需通過構造器來初始化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時,必須按實際寫入順序讀取.