java非常有用的代码段（关键时候可以看看）

获取环境变量

Java代码

. System.getenv("PATH");

. System.getenv("JAVA_HOME");

. 获取系统属性

Java代码

. 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);

. StringTokenizer

Java代码

. // 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);

. StringBuffer(同步)和StringBuilder(非同步)

Java代码

. StringBuilder sb = new StringBuilder();

. sb.append("Hello");

. sb.append("World");

. sb.toString();

. new StringBuffer(a).reverse(); // 反转字符串

. 数字

Java代码

. // 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();

. 日期和时间

Java代码

. // 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);

. 结构化数据

Java代码

. // 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

. 1. 数组：Arrays.sort(strings);

. 2. List：Collections.sort(list);

. 3. 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

. 泛型与foreach

Java代码

. // 泛型

. List<String> myList = new ArrayList<String>();

.

. // foreach

. for (String s : myList) {

. System.out.println(s);

. }

. 面向对象

Java代码

. // 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: 1. 覆盖对象的clone()方法; 2. 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);

. }

. }

. 输入和输出

Java代码

. // 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

. 1. 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

. 2. 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

. 1. 用System.out的println()打印数据

. 2. 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);

. 目录和文件操作

Java代码

. // 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

. 国际化和本地化

Java代码

. // 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.chap11.Widgets");

. String propt = rb.getString("filedialogs.cantopen.string");

. String result = MessageFormat.format(rb.getString("filedialogs.cantopen.format"), data);

. 网络客户端

Java代码

. // 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

. 服务器端: Socket

Java代码

. // 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);

. }

. }

. Java Mail

Java代码

. // 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);

. 数据库访问

Java代码

. // 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();

. 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

Java代码

. // 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"));

. RMI

Java代码

. 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

. 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

. Java线程

Java代码

. // 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

. 内省或“命令类的类”

Java代码

. // 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"

. Java与其他语言的结合

Java代码

. // 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);