Java经典实例

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1. 获取环境变量

System.getenv("PATH");  System.getenv("JAVA_HOME");

2. 获取系统属性

System.getProperty("pencil color");  // 得到属性值  java -Dpencil color=green  System.getProperty("java.specification.version");  // 得到Java版本号  Properties p = System.getProperties();  // 得到所有属性值  p.list(System.out);

3. StringTokenizer
// 能够同时识别, 和 |  StringTokenizer st = new StringTokenizer("Hello, World|of|Java", ", |");  while (st.hasMoreElements()) {       st.nextToken();  }       // 把分隔符视为token  StringTokenizer st = new StringTokenizer("Hello, World|of|Java", ", |",  true); 
4. StringBuffer(同步)和StringBuilder(非同步)
StringBuilder sb = new StringBuilder();  sb.append("Hello");  sb.append("World");  sb.toString();  new StringBuffer(a).reverse();   // 反转字符串  
5. 数字
// 数字与对象之间互相转换 - Integer转int  Integer.intValue();     // 浮点数的舍入    Math.round()    // 数字格式化      NumberFormat            // 整数 -> 二进制字符串      toBinaryString() 或valueOf()            // 整数 -> 八进制字符串  toOctalString()        // 整数 -> 十六进制字符串  toHexString()        // 数字格式化为罗马数字  RomanNumberFormat()        // 随机数  Random r = new Random();  r.nextDouble();  r.nextInt();  

6. 日期和时间
           // 查看当前日期           Date today = new Date();           Calendar.getInstance().getTime();                  // 格式化默认区域日期输出           DateFormat df = DateFormat.getInstance();           df.format(today);                  // 格式化制定区域日期输出           DateFormat df_cn = DateFormat.getDateInstance(DateFormat.FULL, Locale.CHINA);           String now = df_cn.format(today);                  // 按要求格式打印日期           SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");           sdf.format(today);                  // 设置具体日期           GregorianCalendar d1 = new GregorianCalendar(2009, 05, 06);  // 6月6日           GregorianCalendar d2 = new GregorianCalendar();  // 今天           Calendar d3 = Calendar.getInstance();  // 今天           d1.getTime();  // Calendar或GregorianCalendar转成Date格式           d3.set(Calendar.YEAR, 1999);           d3.set(Calendar.MONTH, Calendar.APRIL);           d3.set(Calendar.DAY_OF_MONTH, 12);                  // 字符串转日期           SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");           Date now = sdf.parse(String);                  // 日期加减           Date now = new Date();           long t = now.getTime();           t += 700*24*60*60*1000;           Date then = new Date(t);                  Calendar now = Calendar.getInstance();           now.add(Calendar.YEAR, -2);                  // 计算日期间隔(转换成long来计算)           today.getTime() - old.getTime();                  // 比较日期           Date 类型，就使用equals(), before(), after()来计算           long类型，就使用==, <, >来计算                  // 第几日           使用 Calendar的get()方法           Calendar c = Calendar.getInstance();           c.get(Calendar.YEAR);                  // 记录耗时           long start = System.currentTimeMillis();           long end = System.currentTimeMillis();           long elapsed = end - start;           System.nanoTime();  //毫秒                  // 长整形转换成秒           Double.toString(t/1000D);

7. 结构化数据
           // 数组拷贝           System.arrayCopy(oldArray, 0, newArray, 0, oldArray.length);                  // ArrayList           add(Object o)  // 在末尾添加给定元素           add(int i, Object o)  // 在指定位置插入给定元素           clear()  // 从集合中删除全部元素           Contains(Object o)  // 如果Vector包含给定元素，返回真值           get(int i)  // 返回 指定位置的对象句柄           indexOf(Object o)  // 如果找到给定对象，则返回其索引值；否则，返回-1           remove(Object o)  // 根据引用删除对象           remove(int i)  // 根据 位置删除对象           toArray()  // 返回包含集合对象的数组                  // Iterator           List list = new ArrayList();           Iterator it = list.iterator();           while (it.hasNext())               Object o = it.next();                  // 链表           LinkedList list = new LinkedList();           ListIterator it = list.listIterator();           while (it.hasNext())               Object o = it.next();                  // HashMap           HashMap<String, String> hm = new HashMap<String, String>();           hm.get(key);  // 通过key得到value           hm.put("No1", "Hexinyu");           hm.put("No2", "Sean");           // 方法1: 获取全部键值           Iterator<String> it = hm.values().iterator();           while (it.hasNext()) {                   String myKey = it.next();                   String myValue = hm.get(myKey);               }           // 方法2: 获取全部键值           for (String key : hm.keySet()) {                   String myKey = key;                   String myValue = hm.get(myKey);               }                  // Preferences - 与系统相关的用户设置，类似名-值对           Preferences prefs = Preferences.userNodeForPackage(ArrayDemo.class);           String text = prefs.get("textFontName", "lucida-bright");           String display = prefs.get("displayFontName", "lucida-balckletter");           System.out.println(text);           System.out.println(display);           // 用户设置了新值，存储回去           prefs.put("textFontName", "new-bright");           prefs.put("displayFontName", "new-balckletter");                  // Properties - 类似名-值对，key和value之间，可以用"="，":"或空格分隔，用"#" 和"!"注释           InputStream in = MediationServer.class.getClassLoader().getResourceAsStream("msconfig.properties");           Properties prop = new Properties();           prop.load(in);           in.close();           prop.setProperty(key, value);           prop.getProperty(key);                  // 排序           数组：Arrays.sort(strings);           List：Collections.sort(list);           自定义类：class SubComp implements Comparator               然 后使用Arrays.sort(strings, new SubComp())                  // 两个接口           1.java.lang.Comparable: 提供对象的自然排序，内置于类中              int compareTo(Object o);               boolean equals(Object o2);           2.java.util.Comparator: 提供特定的比较方法              int compare(Object o1, Object o2)                  // 避免重复排序，可以使用TreeMap           TreeMap sorted = new TreeMap(unsortedHashMap);                  // 排除重复元素           Hashset hs - new HashSet();                  // 搜索对象           binarySearch(): 快 速查询 - Arrays, Collections           contains(): 线型搜 索 - ArrayList, HashSet, Hashtable, linkedList, Properties, Vector           containsKey(): 检 查集合对象是否包含给定 - HashMap, Hashtable, Properties, TreeMap           containsValue(): 主 键(或给定值) - HashMap, Hashtable, Properties, TreeMap           indexOf(): 若 找到给定对象，返回其位置 - ArrayList, linkedList, List, Stack, Vector           search(): 线 型搜素 - Stack                  // 集合转数组           toArray();                  // 集合总结           Collection: Set - HashSet, TreeSet           Collection: List - ArrayList, Vector, LinkedList           Map: HashMap, HashTable, TreeMap
8. 泛型与foreach
// 泛型  List<String> myList = new ArrayList<String>();       // foreach  for (String s : myList) {    System.out.println(s);}
9. 面向对象
// toString()格式化          public class ToStringWith {            int x, y;            public ToStringWith(int anX, int aY) {                x = anX;                y = aY;            }            public String toString() {                return "ToStringWith[" + x + "," + y + "]";            }            public static void main(String[] args) {                System.out.println(new ToStringWith(43, 78));            }        }        // 覆盖equals方法          public boolean equals (Object o){            if (o == this)  // 优化                  return true;            if (!(o instanceof EqualsDemo))  // 可投射到这个类                  return false;            EqualsDemo other = (EqualsDemo) o;  // 类型转换              if (int1 != other.int1)  // 按字段比较                  return false;            if (!obj1.equals(other.obj1))                return false;            return true;        }        // 覆盖hashcode方法          private volatile int hashCode = 0;  //延迟初始化          public int hashCode () {            if (hashCode == 0) {                int result = 17;                result = 37 * result + areaCode;            }            return hashCode;        }        // Clone方法          要 克隆对象，必须先做两步:        覆盖对象的clone() 方法;        实现空的Cloneable接口        public class Clone1 implements Cloneable {            public Object clone() {                return super.clone();            }        }        // Finalize方法          Object f = new Object() {            public void finalize() {                System.out.println("Running finalize()");            }        };        Runtime.getRuntime().addShutdownHook(new Thread() {            public void run() {                System.out.println("Running Shutdown Hook");            }        });        在 调用System.exit(0);        的时候，这两个方法将被执行        // Singleton模式          // 实现1          public class MySingleton () {            public static final MySingleton INSTANCE = new MySingleton();                   private MySingleton() {            }        }        // 实现2          public class MySingleton () {            public static MySingleton instance = new MySingleton();                   private MySingleton() {            }        public static MySingleton getInstance () {            return instance;        }               }        // 自定义异常          Exception:        编 译时检查        RuntimeException:        运行时检查        public class MyException extends RuntimeException {            public MyException() {                super();            }            public MyException(String msg) {                super(msg);            }        }

10. 输入和输出
// Stream, Reader, Writer          Stream:        处 理字节流        Reader / Writer:处理字符，通用Unicode        // 从标准输入设备读数据          用System.in的BufferedInputStream() 读取字节        int b = System.in.read();        System.out.println("Read data: " + (char) b);  // 强 制转换为字符          BufferedReader 读取文本        如果从Stream转成Reader，使用 InputStreamReader类        BufferedReader is = new BufferedReader(new                InputStreamReader(System.in));        String inputLine;        while ((inputLine = is.readLine()) != null) {            System.out.println(inputLine);            int val = Integer.parseInt(inputLine);  // 如果inputLine为整数          }        is.close();        // 向标准输出设备写数据          用System.out的println() 打印数据                用PrintWriter打印        PrintWriter pw = new PrintWriter(System.out);        pw.println("The answer is " + myAnswer + " at this time.");        // Formatter类          格 式化打印内容        Formatter fmtr = new Formatter();        fmtr.format("%1$04d - the year of %2$f", 1951, Math.PI);        或 者System.out.printf();        或者System.out.format();        // 原始扫描      void doFile(Reader is) {        int c;        while ((c = is.read()) != -1) {            System.out.println((char) c);        }    }    // Scanner扫描      Scanner 可以读取File, InputStream, String, Readable           try    {        Scanner scan = new Scanner(new File("a.txt"));        while (scan.hasNext()) {            String s = scan.next();        }    } catch(    FileNotFoundException e)    {        e.printStackTrace();    }}    // 读取文件      BufferedReader is = new BufferedReader(new FileReader("myFile.txt"));    BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream("bytes.bat"));      is.close();            bos.close();            // 复制文件              BufferedIutputStream is=new BufferedIutputStream(new FileIutputStream("oldFile.txt"));            BufferedOutputStream os=new BufferedOutputStream(new FileOutputStream("newFile.txt"));            int b;            while((b=is.read())!=-1){            os.write(b);            }            is.close();            os.close();            // 文件读入字符串              StringBuffer sb=new StringBuffer();            char[]b=new char[8192];            int n;            // 读一个块，如果有字符，加入缓冲区              while((n=is.read(b))>0){            sb.append(b,0,n);            }            return sb.toString();            // 重定向标准流              String logfile="error.log";            System.setErr(new PrintStream(new FileOutputStream(logfile)));            // 读写不同字符集文本              BufferedReader chinese=new BufferedReader(new InputStreamReader(new FileInputStream("chinese.txt"),"ISO8859_1"));            PrintWriter standard=new PrintWriter(new OutputStreamWriter(new FileOutputStream("standard.txt"),"UTF-8"));            // 读取二进制数据              DataOutputStream os=new DataOutputStream(new FileOutputStream("a.txt"));            os.writeInt(i);            os.writeDouble(d);            os.close();            // 从指定位置读数据              RandomAccessFile raf=new RandomAccessFile(fileName,"r");  // r表示已 只读打开              raf.seek(15);  // 从15开始读              raf.readInt();            raf.radLine();            // 串行化对象              对象串 行化，必须实现Serializable接口            // 保存 数据到磁盘              ObjectOutputStream os=new ObjectOutputStream(new BufferedOutputStream(new FileOutputStream(FILENAME)));            os.writeObject(serialObject);            os.close();            // 读出数据              ObjectInputStream is=new ObjectInputStream(new FileInputStream(FILENAME));            is.readObject();            is.close();            // 读写Jar或Zip文档              ZipFile zippy=new ZipFile("a.jar");            Enumeration all=zippy.entries();  // 枚举值列出所有文件清单              while(all.hasMoreElements()){            ZipEntry entry=(ZipEntry)all.nextElement();            if(entry.isFile())            println("Directory: "+entry.getName());            // 读写文件              FileOutputStream os=new FileOutputStream(entry.getName());            InputStream is=zippy.getInputStream(entry);            int n=0;            byte[]b=new byte[8092];            while((n=is.read(b))>0){            os.write(b,0,n);            is.close();            os.close();            }            }            // 读写gzip文档              FileInputStream fin=new FileInputStream(FILENAME);            GZIPInputStream gzis=new GZIPInputStream(fin);            InputStreamReader xover=new InputStreamReader(gzis);            BufferedReader is=new BufferedReader(xover);            String line;            while((line=is.readLine())!=null)            System.out.println("Read: "+line);
11. 目录和文件操作
// 获取文件信息          exists():如 果文件存在，返回true        getCanonicalPath():获 取全名        getName():文件名        getParent():父 目录        canRead():如果文件可读，返回true        canWrite():如 果文件可写，返回true        lastModified():文 件更新时间        length():文件大小        isFile():如 果是文件，返回true        ifDirectory():如 果是目录，返回true        要 调用文件的这些方法，必须        File f = new File(fileName);        // 创建文件          File f = new File("c:\\test\\mytest.txt");        f.createNewFile();  // 创建mytest.txt文件到test目录下          // 修改文件名          File f = new File("c:\\test\\mytest.txt");        f.renameTo(new File("c:\\test\\google.txt"));        把 mytest.txt修改成google.txt        // 删除文件          File f = new File("c:\\test\\mytest.txt");        f.delete();        // 临时文件          File f = new File("C:\\test");  // 指定一个文件夹          // 在test文件夹中创建foo前缀，tmp后缀的临时文件          File tmp = File.createTempFile("foo", "tmp", f);        tmp.deleteOnExit();  // 在程序结束时删除该临时文件          // 更改文件属性          setReadOnly():设 置为只读        setlastModified():设置最后更改时间        // 列出当前文件夹的文件列表          String[] dir = new java.io.File(".").list();        java.util.Arrays.sort(dir);        for (int i = 0; i < dir.length; i++) {            System.out.println(dir[i]);        }        // 过滤文件列表          class OnlyJava implements FilenameFilter {            public boolean accept(File dir, String s) {                if (s.endsWith(".java") || s.endsWith(".class") || s.endsWith(".jar"))                    return true;            }        }        // 获取根目录          File[] rootDir = File.listRoots();        for (int i = 0; i < rootDir.length; i++) {            System.out.println(rootDir[i]);        }        // 创建新目录          new File("/home/ian/bin").mkdir();  // 如果"/home/ian"存在，则可以创建bin目录          new File("/home/ian/bin").mkdirs();  // 如果"/home/ian"不存在，会创建所有的目录  

12. 国际化和本地化
// I18N资源          ResourceBundle rb = ResourceBundle.getBundle("Menus");        String label = rb.getString("exit.label");        // ResourceBundle相当于名值对，获取Menus按钮的区域属性          Menus_cn.properties:不 同区域的属性文件        // 列出有效区域          Locale[] list = Locale.getAvailableLocales()；        // 指定区域          Locale cnLocale = Locale.CHINA;        // 设置默认区域          Locale.setDefault(Locale.CHINA);        // 格式化消息          public class MessageFormatDemo {            static Object[] data = {                    new java.util.Date(),                    "myfile.txt",                    "could nto be opened"            };            public static void main(String[] args) {                String result = MessageFormat.format("At {0,time} on {0,date}, {1} {2}.", data);                System.out.println(result);            }        }        输 出:At 10:10:08 on 2009 - 6 - 18, myfile.txt could nto be opened.        // 从资源文件中读消息          Widgets.properties 在com.sean.cook.chap11下        ResourceBundle rb = ResourceBundle.getBundle("com.sean.cook.chapWidgets");        String propt = rb.getString("filedialogs.cantopen.string");        String result = MessageFormat.format(rb.getString("filedialogs.cantopen.format"), data);
13. 网络客户端
// 访问服务器          Socket socket = new Socket("127.0.0.1", 8080);        // todo something          socket.close();        // 查找网络地址          InetAddress.getByName(hostName).getHostAddress()); // 根据主机名得到IP地址          InetAddress.getByName(ipAddr).getHostName()); // 根据IP地址得到主机名          // 连接具体异常          UnknownHostException                NoRouteToHostException        ConnectException        // Socket读写文本数据          BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));        String remoteTime = in.readline();        PrintWriter out = new PrintWriter(socket.getOutputStream(), true);        out.print("send message to client \r\n");        out.flush();        // Socket读写二进制数据          DataInputStream in = new DataInputStream(new BufferedInputStream(socket.getInputStream()));        long remoteTime = (long) (in.readUnsignedByte() << 24);        DataOutputStream out = new DataOutputStream(socket.getOutputStream(), true);        // Socket读写串行化数据          ObjectInputStream in = new ObjectInputStream(new BufferedInputStream(socket.getInputStream()));        Object o = in.readObject();        if (o instanceof Date) // 验证对象类型              ObjectOutputStream out = new ObjectOutputStream(socket.getOutputStream(), true);        // UDP数据报          private final static int PACKET_SIZE = 1024;        String host = "EV001B389673DE";        InetAddress serverAddr = InetAddress.getByName(host);        DatagramSocket socket = new DatagramSocket();        byte[] buffer = new byte[PACKET_SIZE]; // 分配数据缓冲空间          DatagramPacket packet = new DatagramPacket(buffer, PACKET_SIZE, serverAddr, 8080);        packet.setLength(PACKET_SIZE - 1); // 设置数据长度          socket.send(packet);        socket.receive(packet); // 接收数据  

14. 服务器端: Socket 
// 创建ServerSocket        ServerSocket serverSocket;        Socket clientSocket;        serverSocket = new ServerSocket(9999);        while ((clientSocket = serverSocket.accept()) != null) {            System.out.println("Accept from client " + s.getInetAddress());            s.close();        }        // 监听内部网        public static final short PORT = 9999;        public static final String INSIDE_HOST = "acmewidgets-inside"; // 网络接口名        public static final int BACKLOG = 10; // 待发数        serverSocket = new ServerSocket(PORT, BACKLOG, InetAddress.getByName(INSIDE_HOST));        // 返回相应对象        ServerSocket serverSocket = new ServerSocket(9999);        ;        Socket clientSocket;        BufferedReader in = null;        PrintWriter out = null;        while (true) {            clientSocket = serverSocket.accept();            in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream(), "8859_1"));            out = new PrintWriter(new OutputStreamWriter(clientSocket.getOutputStream(), "8859_1"), true);            String echoLine;            while ((echoLine = in.readLine()) != null) {                System.out.println("Read " + echoLine);                out.print(echoLine + "\r\n");            }        }        以 上例子返回字符串，如果返回二进制，则使用DataOutputStream；返回对象，使用ObjectOutputStream        // 处理多客户端        需要 把接收数据的处理放入多线程中        public class EchoServerThreaded {            public static final int ECHOPORT = 7;            public static final int NUM_THREADS = 4;            public static void main(String[] av) {                new EchoServerThreaded(ECHOPORT, NUM_THREADS);            }            public EchoServerThreaded2(int port, int numThreads) {                ServerSocket servSock;                Socket clientSocket;                try {                    servSock = new ServerSocket(ECHOPORT);                } catch (IOException e) {                    throw new RuntimeException("Could not create ServerSocket " + e);                }                for (int i = 0; i < numThreads; i++) {                    new Handler(servSock, i).start();                }            }        }        class Handler extends Thread {            ServerSocket servSock;            int threadNumber;            Handler(ServerSocket s, int i) {                super();                servSock = s;                threadNumber = i;                setName("Thread " + threadNumber);            }            public void run() {                while (true) {                    try {                        System.out.println(getName() + " waiting");                        Socket clientSocket;                        synchronized (servSock) {                            clientSocket = servSock.accept();                        }                        System.out.println(getName() + " starting, IP=" + clientSocket.getInetAddress());                        BufferedReader is = new BufferedReader(new InputStreamReader(                                clientSocket.getInputStream()));                        PrintStream os = new PrintStream(clientSocket.getOutputStream(), true);                        String line;                        while ((line = is.readLine()) != null) {                            os.print(line + "\r\n");                            os.flush();                        }                        System.out.println(getName() + " ENDED ");                        clientSocket.close();                    } catch (IOException ex) {                        System.out.println(getName() + ": IO Error on socket " + ex);                        return;                    }                }            }        }        // 使用SSL和JSSE保护Web服务器        SSLServerSocketFactory ssf = (SSLServerSocketFactory) SSLServerSocketFactory.getDefault()；        ServerSocket serverSocket = ssf.createServerSocket(8080);        // Log4j        Level 级别:DEBUG<INFO<WARN<ERROR<FATAL<OFF        Appender:        输 出信息        ConsoleAppender:        输出控制台 System.out        // 找到网络接口        Enumeration list = NetworkInterface.getNetworkInterfaces();        while (list.hasMoreElements()) {            NetworkInterface iface = (NetworkInterface) list.nextElement();            System.out.println(iface.getDisplayName());            Enumeration addrs = iface.getInetAddresses();            while (addrs.hasMoreElements()) {                InetAddress addr = (InetAddress) addrs.nextElement();                System.out.println(addr);            }        }

15. Java Mail
// 发送Mail          protected String msgRecIp = "hxydream@163.com";        protected String msgSubject = "babytree";        protected String msgCc = "nobody@erewhon.com";        protected String msgBody = "test body";        protected Session session;        protected Message msg;        public void doSend () {            // 创建属性文件              Properties props = new Properties();            props.put("mail.smtp.host", "mailhost");            // 创建Session对象              session = Session.getDefaultInstance(props, null);            session.setDebug(true);            msg = new MimeMessage(session); // 创建邮件              msg.setFrom(new InternetAddress("nobody@host.domain"));            InternetAddress toAddr = new InternetAddress(msgRecIp);            msg.addRecipient(Message.RecipientType.TO, toAddr);            InternetAddress ccAddr = new InternetAddress(msgCc);            msg.addRecipient(Message.RecipientType.CC, ccAddr);            msg.setSubject(msgSubject);            msg.setText(msgBody);            Transport.send(msg);        }        // 发送MIME邮件          Multipart mp = new MimeMultipart();        BodyPart textPart = new MimeBodyPart();        textPart.setText(message_body);  // 设置类型"text/plain"          BodyPart pixPart = new MimeBodyPart();        pixPart.setContent(html_data, "text/html");        mp.addBodyPart(textPart);        mp.addBodyPart(pixPart);        mesg.setContent(mp);        Transport.send(mesg);        // 读Mail          Store store = session.getStore(protocol);        store.connect(host, user, password);        Folder rf;        rf = store.getFolder(root);        rf = store.getDefaultFolder();        rf.open(Folder.READ_WRITE);


16. 数据库访问 
// JDO          Properties p = new Properties();        p.load(new FileInputStream("jdo.properties"));        PersistenceManagerFactory pmf = JDOHelper.getPersistenceManagerFactory(p);        PersistenceManager pm = pmf.getPersistenceManager();        // 提交数据          pm.currentTransaction().begin();        if (o instanceof Collection) {            pm.makePersistentAll((Collection) o);        } else {            pm.makePersistent(o);        }        pm.currentTransaction().commit();        pm.close();        // 取出数据          Object[] data = new Object[3];        pm.retrieveAll(data);        for (int i = 0; i < data.length; i++) {            System.out.println(data[i]);        }        pm.close();        // 数据操作          Class clz = Class.forName("oracle.jdbc.driver.OracleDriver");        String dbUrl = "jdbc:oracle:thin:@192.168.0.23:1521#:nms";        Connection conn = DriverManager.getConnection(dbUrl, "su", "1234");        Statement stmt = conn.createStatement();        ResultSet rs = stmt.executeQuery("select * from pmtable");        while (rs.next()) {            String name = rs.getString(1);            String otherName = rs.getString("name");        }        // 使用PreparedStatement提高性能，除了查询，都使用executeUpdate执行操作           PreparedStatement pstmt = conn.prepareStatement("select * from pmtable where name = ?");        pstmt.setString(1, "sean");        ResultSet rs = pstmt.executeQuery();        // 调用存储过程                     CallableStatement cs = conn.prepareCall("{ call ListDefunctUsers }");        ResultSet rs = cs.executeQuery();        // 显示数据库表信息           DatabaseMetaData meta = conn.getMetaData();        meta.getDatabaseProductName();        meta.getDatabaseProductVersion();        meta.getDefaultTransactionIsolation();
17. XML
    SAX: 在读取文档提取相应的标记事件(元素起始、元素结束、文档起始)    DOM: 在内存中构造与文档中元素相应的树，可以遍历、搜索、修改    DTD: 验证文档是否正确    JAXP: 用于XML处理的Java API    Castor: 开源项目，用于Java对象与XML映射
// 从对象中生成XML        private final static String FILENAME = "serial.xml";        public static void main (String[]args) throws IOException {            String a = "hard work and best callback";            new SerialDemoXML().write(a);            new SerialDemoXML().dump();        }        public void write (Object obj) throws IOException {            XMLEncoder os = new XMLEncoder(new BufferedOutputStream(new FileOutputStream(FILENAME)));            os.writeObject(obj);            os.close();        }        public void dump () throws IOException {            XMLDecoder out = new XMLDecoder(new BufferedInputStream(new FileInputStream(FILENAME)));            System.out.println(out.readObject());            out.close();        }        serial.xml 格式内容如下:           <?xml version = "1.0" encoding = "UTF-8" ?>           <java version = "1.6.0_02" class="java.beans.XMLDecoder" >                       <string > hard work and best callback</string >                   </java >                控 制台输出        hard work and best callback        // XSLT转换XML        XSLT 可以用来对输出格式进行各种控制        Transformer tx = TransformerFactory.newInstance().newTransformer(new StreamSource("people.xml"));        tx.transform(new StreamSource("people.xml"), new StreamResult("people.html"));        // 用SAX解析XML - 主要用于查找关键元素，不用全文遍历           public SaxLister() throws SAXException, IOException {            XMLReader parser = XMLReaderFactory.createXMLReader("org.apache.xerces.parsers.SAXParser");            parser.setContentHandler(new PeopleHandler());            parser.parse("C:\\StudySource\\javacooksrc2\\xml\\people.xml");        }        class PeopleHandler extends DefaultHandler {            boolean parent = false;            boolean kids = false;            public void startElement(String nsURI, String localName, String rawName, Attributes attr) throws SAXException {                System.out.println("startElement: " + localName + "," + rawName);                if (rawName.equalsIgnoreCase("name"))                    parent = true;                if (rawName.equalsIgnoreCase("children"))                    kids = true;            }            public void characters(char[] ch, int start, int length) {                if (parent) {                    System.out.println("Parent: " + new String(ch, start, length));                    parent = false;                } else if (kids) {                    System.out.println("Children: " + new String(ch, start, length));                    kids = false;                }            }            public PeopleHandler() throws SAXException {                super();            }        }        // DOM解析XML - 遍历整个树        String uri = "file:" + new File("C:\\StudySource\\javacooksrc2\\xml\\people.xml").getAbsolutePath();        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();        DocumentBuilder builder = factory.newDocumentBuilder();        Document doc = builder.parse(uri);        NodeList nodes = doc.getChildNodes();        for (int i = 0; i < nodes.getLength(); i++) {            Node n = nodes.item(i);            switch (n.getNodeType()) {                case Node.ELEMENT_NODE:                    // todo                    break;                case Node.TEXT_NODE:                    // todo                    break;            }        }        // 使用DTD或者XSD验证        定 义好DTD或XSD文件        XmlDocument doc = XmlDocument.createXmlDocument(uri, true);        // 用DOM生成XML        DocumentBuilderFactory fact = DocumentBuilderFactory.newInstance();        DocumentBuilder parser = fact.newDocumentBuilder();        Document doc = parser.newDocument();        Node root = doc.createElement("Poem");        doc.appendChild(root);        Node stanza = doc.createElement("Stanza");        root.appendChild(stanza);        Node line = doc.createElement("Line");        stanza.appendChild(line);        line.appendChild(doc.createTextNode("Once, upon a midnight dreary"));        line = doc.createElement("Line");        stanza.appendChild(line);        line.appendChild(doc.createTextNode("While I pondered, weak and weary"));
18. RMI
a.定义 客户端与服务器之间的通信接口        public interface RemoteDate extends Remote {            public Date getRemoteDate() throws RemoteException;            public final static String LOOKUPNAME = "RemoteDate";        }        b.编 写RMI服务器        public class RemoteDateImpl extends UnicastRemoteObject implements RemoteDate {            public RemoteDateImpl() throws RemoteException {                super();            }            public Date getRemoteDate() throws RemoteException {                return new Date();            }        }        RemoteDateImpl im = new RemoteDateImpl();        System.out.println("DateServer starting...");        Naming.rebind(RemoteDate.LOOKUPNAME, im);        System.out.println("DateServer ready.");        c.运 行rmic生成stub        javac RemoteDateImpl.java        rmic RemoteDateImpl        d.编 写客户端        netConn = (RemoteDate) Naming.lookup(RemoteDate.LOOKUPNAME);        Date today = netConn.getRemoteDate();        System.out.println(today.toString());        e.确 保RMI注册表运行        rmiregistry        f.启 动服务器        java RemoteDateImpl        g.运 行客户端        java DateClient
19. 包和包装机制
jar cvf /tmp/test.jar .  // 当前目录压缩到test.jar中    jar xvf /tmp/test.jar  // 把test.jar解压到当前目录    从指定class运行jar文件    a. Main-Class: HelloWord  // 注意中间有一个空格    b. jar cvmf manifest.mf hello.jar HelloWorld.class    c. java -jar hello.jar
20. Java线程
// 停止线程 - 不要使用stop()方法          private boolean done = false;        public void run () {            while (!done) {                //todo              }        }        public void shutDown () {            done = true;        }        可 以调用shutDown () 方法来结束线程        // 如果读取IO的时候出现堵塞，那么可以使用下面方法          public void shutDown () throws IOException {            if (io != null)                io.close();        }        // 启动一线程，等待控制台输入，使用join()方法来暂停当前线程，直到其他线程调用          Thread t = new Thread() {            public void run() {                System.out.println("Reading");                try {                    System.in.read();                } catch (IOException e) {                    System.err.println(e);                }                System.out.println("Thread finished.");            }        };        System.out.println("Starting");        t.start();        System.out.println("Joining");        try {            t.join();        } catch (InterruptedException e) {            System.out.println("Who dares imterrupt my sleep?");        }        System.out.println("Main finished.");        // 加锁保证同步          Lock lock = new ReentrantLock();        try {            lock.lock();            // todo          } finally {            lock.unlock();        }        线 程通信wait (), notify(), notifyAll()        生产者 - 消费者模式        Executors
21. 内省或“命令类的类”
// 反射          Class c = Class.forName("java.lang.String");        Constructor[] cons = c.getConstructors();        for (int i = 0; i < cons.length; i++) {            System.out.println(cons[i].toString());        }        Method[] meths = c.getMethods();        for (int i = 0; i < meths.length; i++) {            System.out.println(meths[i].toString());        }        // 动态装载类          Class c = Class.forName("java.lang.String");        Object obj = c.newInstance();        // 通过反射调用类的方法          class X {            public void master(String s) {                System.out.println("Working on \"" + s + "\"");            }        }        Class clx = X.class;        Class[] argTypes = {String.class};        Method worker = clx.getMethod("master", argTypes);        Object[] theData = {"Chocolate chips"};        worker.invoke(new X(), theData);        输 出:Working on "Chocolate chips"
22. Java与其他语言的结合
// 执行CMD命令，在Eclipse控制台输出          Process p = Runtime.getRuntime().exec("C:/StudySource/ver.cmd");        p.waitFor(); // 等待命令执行完          BufferedReader br = new BufferedReader(new InputStreamReader(p.getInputStream()));        String s;        while ((s = br.readLine()) != null)            System.out.println(s);        // 调用Jython - 计算22.0/7          BSFManager manager = new BSFManager();        String[] fntypes = {".py"};        manager.registerScriptingEngine("jython", "org.apache.bsf.engines.jython.JythonEngine", fntypes);        Object r = manager.eval("jython", "testString", 0, 0, "22.0/7");        System.out.println("Result type is " + r.getClass().getName());        System.out.println("Result value is " + r);
原文：http://blog.csdn.net/qq_35101189/article/details/62217430

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