22个Java经典实例 带完美注释
1. 获取环境变量
Java代码
1. System.getenv("
ATH");
2. System.getenv("JAVA_HOME");
2. 获取系统属性
Java代码
1. System.getProperty("pencil color"); // 得到属性值
2. java -Dpencil color=green
3. System.getProperty("java.specification.version"); // 得到Java版本号
4. Properties p = System.getProperties(); // 得到所有属性值
5. p.list(System.out);
3. StringTokenizer
Java代码
1. // 能够同时识别, 和 |
2. StringTokenizer st = new StringTokenizer("Hello, World|of|Java", ", |");
3. while (st.hasMoreElements()) {
4. st.nextToken();
5. }
6.
7. // 把分隔符视为token
8. StringTokenizer st = new StringTokenizer("Hello, World|of|Java", ", |", true);
4. StringBuffer(同步)和StringBuilder(非同步)
Java代码
1. StringBuilder sb = new StringBuilder();
2. sb.append("Hello");
3. sb.append("World");
4. sb.toString();
5. new StringBuffer(a).reverse(); // 反转字符串
5. 数字
Java代码
1. // 数字与对象之间互相转换 - Integer转int
2. Integer.intValue();
3.
4. // 浮点数的舍入
5. Math.round()
6.
7. // 数字格式化
8. NumberFormat
9.
10. // 整数 -> 二进制字符串
11. toBinaryString() 或valueOf()
12.
13. // 整数 -> 八进制字符串
14. toOctalString()
15.
16. // 整数 -> 十六进制字符串
17. toHexString()
18.
19. // 数字格式化为罗马数字
20. RomanNumberFormat()
21.
22. // 随机数
23. Random r = new Random();
24. r.nextDouble();
25. r.nextInt();
6. 日期和时间
Java代码
1. // 查看当前日期
2. Date today = new Date();
3. Calendar.getInstance().getTime();
4.
5. // 格式化默认区域日期输出
6. DateFormat df = DateFormat.getInstance();
7. df.format(today);
8.
9. // 格式化制定区域日期输出
10. DateFormat df_cn = DateFormat.getDateInstance(DateFormat.FULL, Locale.CHINA);
11. String now = df_cn.format(today);
12.
13. // 按要求格式打印日期
14. SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
15. sdf.format(today);
16.
17. // 设置具体日期
18. GregorianCalendar d1 = new GregorianCalendar(2009, 05, 06); // 6月6日
19. GregorianCalendar d2 = new GregorianCalendar(); // 今天
20. Calendar d3 = Calendar.getInstance(); // 今天
21. d1.getTime(); // Calendar或GregorianCalendar转成Date格式
22. d3.set(Calendar.YEAR, 1999);
23. d3.set(Calendar.MONTH, Calendar.APRIL);
24. d3.set(Calendar.DAY_OF_MONTH, 12);
25.
26. // 字符串转日期
27. SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
28. Date now = sdf.parse(String);
29.
30. // 日期加减
31. Date now = new Date();
32. long t = now.getTime();
33. t += 700*24*60*60*1000;
34. Date then = new Date(t);
35.
36. Calendar now = Calendar.getInstance();
37. now.add(Calendar.YEAR, -2);
38.
39. // 计算日期间隔(转换成long来计算)
40. today.getTime() - old.getTime();
41.
42. // 比较日期
43. Date 类型，就使用equals(), before(), after()来计算
44. long类型，就使用==, <, >来计算
45.
46. // 第几日
47. 使用 Calendar的get()方法
48. Calendar c = Calendar.getInstance();
49. c.get(Calendar.YEAR);
50.
51. // 记录耗时
52. long start = System.currentTimeMillis();
53. long end = System.currentTimeMillis();
54. long elapsed = end - start;
55. System.nanoTime(); //毫秒
56.
57. // 长整形转换成秒
58. Double.toString(t/1000D);
7. 结构化数据
Java代码
1. // 数组拷贝
2. System.arrayCopy(oldArray, 0, newArray, 0, oldArray.length);
3.
4. // ArrayList
5. add(Object o) // 在末尾添加给定元素
6. add(int i, Object o) // 在指定位置插入给定元素
7. clear() // 从集合中删除全部元素
8. Contains(Object o) // 如果Vector包含给定元素，返回真值
9. get(int i) // 返回 指定位置的对象句柄
10. indexOf(Object o) // 如果找到给定对象，则返回其索引值；否则，返回-1
11. remove(Object o) // 根据引用删除对象
12. remove(int i) // 根据 位置删除对象
13. toArray() // 返回包含集合对象的数组
14.
15. // Iterator
16. List list = new ArrayList();
17. Iterator it = list.iterator();
18. while (it.hasNext())
19. Object o = it.next();
20.
21. // 链表
22. LinkedList list = new LinkedList();
23. ListIterator it = list.listIterator();
24. while (it.hasNext())
25. Object o = it.next();
26.
27. // HashMap
28. HashMap<String, String> hm = new HashMap<String, String>();
29. hm.get(key); // 通过key得到value
30. hm.put("No1", "Hexinyu");
31. hm.put("No2", "Sean");
32. // 方法1: 获取全部键值
33. Iterator<String> it = hm.values().iterator();
34. while (it.hasNext()) {
35. String myKey = it.next();
36. String myValue = hm.get(myKey);
37. }
38. // 方法2: 获取全部键值
39. for (String key : hm.keySet()) {
40. String myKey = key;
41. String myValue = hm.get(myKey);
42. }
43.
44. // Preferences - 与系统相关的用户设置，类似名-值对
45. Preferences prefs = Preferences.userNodeForPackage(ArrayDemo.class);
46. String text = prefs.get("textFontName", "lucida-bright");
47. String display = prefs.get("displayFontName", "lucida-balckletter");
48. System.out.println(text);
49. System.out.println(display);
50. // 用户设置了新值，存储回去
51. prefs.put("textFontName", "new-bright");
52. prefs.put("displayFontName", "new-balckletter");
53.
54. // Properties - 类似名-值对，key和value之间，可以用"="，":"或空格分隔，用"#" 和"!"注释
55. InputStream in = MediationServer.class.getClassLoader().getResourceAsStream("msconfig.properties");
56. Properties prop = new Properties();
57. prop.load(in);
58. in.close();
59. prop.setProperty(key, value);
60. prop.getProperty(key);
61.
62. // 排序
63. 1. 数组：Arrays.sort(strings);
64. 2. List：Collections.sort(list);
65. 3. 自定义类：class SubComp implements Comparator
66. 然 后使用Arrays.sort(strings, new SubComp())
67.
68. // 两个接口
69. 1. java.lang.Comparable: 提供对象的自然排序，内置于类中
70. int compareTo(Object o);
71. boolean equals(Object o2);
72. 2. java.util.Comparator: 提供特定的比较方法
73. int compare(Object o1, Object o2)
74.
75. // 避免重复排序，可以使用TreeMap
76. TreeMap sorted = new TreeMap(unsortedHashMap);
77.
78. // 排除重复元素
79. Hashset hs - new HashSet();
80.
81. // 搜索对象
82. binarySearch(): 快 速查询 - Arrays, Collections
83. contains(): 线型搜 索 - ArrayList, HashSet, Hashtable, linkedList, Properties, Vector
84. containsKey(): 检 查集合对象是否包含给定 - HashMap, Hashtable, Properties, TreeMap
85. containsValue(): 主 键(或给定值) - HashMap, Hashtable, Properties, TreeMap
86. indexOf(): 若 找到给定对象，返回其位置 - ArrayList, linkedList, List, Stack, Vector
87. search(): 线 型搜素 - Stack
88.
89. // 集合转数组
90. toArray();
91.
92. // 集合总结
93. Collection: Set - HashSet, TreeSet
94. Collection: List - ArrayList, Vector, LinkedList
95. Map: HashMap, HashTable, TreeMap
8. 泛型与foreach
Java代码
1. // 泛型
2. List<String> myList = new ArrayList<String>();
3.
4. // foreach
5. for (String s : myList) {
6. System.out.println(s);
7. }
9. 面向对象
Java代码
1. // toString()格式化
2. public class ToStringWith {
3. int x, y;
4. public ToStringWith(int anX, int aY) {
5. x = anX;
6. y = aY;
7. }
8. public String toString() {
9. return "ToStringWith[" + x + "," + y + "]";
10. }
11. public static void main(String[] args) {
12. System.out.println(new ToStringWith(43, 78));
13. }
14. }
15.
16. // 覆盖equals方法
17. public boolean equals(Object o) {
18. if (o == this) // 优化
19. return true;
20. if (!(o instanceof EqualsDemo)) // 可投射到这个类
21. return false;
22. EqualsDemo other = (EqualsDemo)o; // 类型转换
23. if (int1 != other.int1) // 按字段比较
24. return false;
25. if (!obj1.equals(other.obj1))
26. return false;
27. return true;
28. }
29.
30. // 覆盖hashcode方法
31. private volatile int hashCode = 0; //延迟初始化
32. public int hashCode() {
33. if (hashCode == 0) {
34. int result = 17;
35. result = 37 * result + areaCode;
36. }
37. return hashCode;
38. }
39.
40. // Clone方法
41. 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
42. public class Clone1 implements Cloneable {
43. public Object clone() {
44. return super.clone();
45. }
46. }
47.
48. // Finalize方法
49. Object f = new Object() {
50. public void finalize() {
51. System.out.println("Running finalize()");
52. }
53. };
54. Runtime.getRuntime().addShutdownHook(new Thread() {
55. public void run() {
56. System.out.println("Running Shutdown Hook");
57. }
58. });
59. 在 调用System.exit(0);的时候，这两个方法将被执行
60.
61. // Singleton模式
62. // 实现1
63. public class MySingleton() {
64. public static final MySingleton INSTANCE = new MySingleton();
65. private MySingleton() {}
66. }
67. // 实现2
68. public class MySingleton() {
69. public static MySingleton instance = new MySingleton();
70. private MySingleton() {}
71. public static MySingleton getInstance() {
72. return instance;
73. }
74. }
75.
76. // 自定义异常
77. Exception: 编 译时检查
78. RuntimeException: 运行时检查
79. public class MyException extends RuntimeException {
80. public MyException() {
81. super();
82. }
83. public MyException(String msg) {
84. super(msg);
85. }
86. }
10. 输入和输出
Java代码
1. // Stream, Reader, Writer
2. Stream: 处 理字节流
3. Reader/Writer: 处理字符，通用Unicode
4.
5. // 从标准输入设备读数据
6. 1. 用System.in的BufferedInputStream()读取字节
7. int b = System.in.read();
8. System.out.println("Read data: " + (char)b); // 强 制转换为字符
9. 2. BufferedReader 读取文本
10. 如果从Stream转成Reader，使用 InputStreamReader类
11. BufferedReader is = new BufferedReader(new
12. InputStreamReader(System.in));
13. String inputLine;
14. while ((inputLine = is.readLine()) != null) {
15. System.out.println(inputLine);
16. int val = Integer.parseInt(inputLine); // 如果inputLine为整数
17. }
18. is.close();
19.
20. // 向标准输出设备写数据
21. 1. 用System.out的println()打印数据
22. 2. 用PrintWriter打印
23. PrintWriter pw = new PrintWriter(System.out);
24. pw.println("The answer is " + myAnswer + " at this time.");
25.
26. // Formatter类
27. 格 式化打印内容
28. Formatter fmtr = new Formatter();
29. fmtr.format("%1$04d - the year of %2$f", 1951, Math.PI);
30. 或 者System.out.printf();或者System.out.format();
31.
32. // 原始扫描
33. void doFile(Reader is) {
34. int c;
35. while ((c = is.read()) != -1) {
36. System.out.println((char)c);
37. }
38. }
39.
40. // Scanner扫描
41. Scanner 可以读取File, InputStream, String, Readable
42. try {
43. Scanner scan = new Scanner(new File("a.txt"));
44. while (scan.hasNext()) {
45. String s = scan.next();
46. }
47. } catch (FileNotFoundException e) {
48. e.printStackTrace();
49. }
50. }
51.
52. // 读取文件
53. BufferedReader is = new BufferedReader(new FileReader("myFile.txt"));
54. BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream("bytes.bat"));
55. is.close();
56. bos.close();
57.
58. // 复制文件
59. BufferedIutputStream is = new BufferedIutputStream(new FileIutputStream("oldFile.txt"));
60. BufferedOutputStream os = new BufferedOutputStream(new FileOutputStream("newFile.txt"));
61. int b;
62. while ((b = is.read()) != -1) {
63. os.write(b);
64. }
65. is.close();
66. os.close();
67.
68. // 文件读入字符串
69. StringBuffer sb = new StringBuffer();
70. char[] b = new char[8192];
71. int n;
72. // 读一个块，如果有字符，加入缓冲区
73. while ((n = is.read(b)) > 0) {
74. sb.append(b, 0, n);
75. }
76. return sb.toString();
77.
78. // 重定向标准流
79. String logfile = "error.log";
80. System.setErr(new PrintStream(new FileOutputStream(logfile)));
81.
82. // 读写不同字符集文本
83. BufferedReader chinese = new BufferedReader(new InputStreamReader(new FileInputStream("chinese.txt"), "ISO8859_1"));
84. PrintWriter standard = new PrintWriter(new OutputStreamWriter(new FileOutputStream("standard.txt"), "UTF-8"));
85.
86. // 读取二进制数据
87. DataOutputStream os = new DataOutputStream(new FileOutputStream("a.txt"));
88. os.writeInt(i);
89. os.writeDouble(d);
90. os.close();
91.
92. // 从指定位置读数据
93. RandomAccessFile raf = new RandomAccessFile(fileName, "r"); // r表示已 只读打开
94. raf.seek(15); // 从15开始读
95. raf.readInt();
96. raf.radLine();
97.
98. // 串行化对象
99. 对象串 行化，必须实现Serializable接口
100. // 保存 数据到磁盘
101. ObjectOutputStream os = new ObjectOutputStream(new BufferedOutputStream(new FileOutputStream(FILENAME)));
102. os.writeObject(serialObject);
103. os.close();
104. // 读出数据
105. ObjectInputStream is = new ObjectInputStream(new FileInputStream(FILENAME));
106. is.readObject();
107. is.close();
108.
109. // 读写Jar或Zip文档
110. ZipFile zippy = new ZipFile("a.jar");
111. Enumeration all = zippy.entries(); // 枚举值列出所有文件清单
112. while (all.hasMoreElements()) {
113. ZipEntry entry = (ZipEntry)all.nextElement();
114. if (entry.isFile())
115. println("Directory: " + entry.getName());
116.
117. // 读写文件
118. FileOutputStream os = new FileOutputStream(entry.getName());
119. InputStream is = zippy.getInputStream(entry);
120. int n = 0;
121. byte[] b = new byte[8092];
122. while ((n = is.read(b)) > 0) {
123. os.write(b, 0, n);
124. is.close();
125. os.close();
126. }
127. }
128.
129. // 读写gzip文档
130. FileInputStream fin = new FileInputStream(FILENAME);
131. GZIPInputStream gzis = new GZIPInputStream(fin);
132. InputStreamReader xover = new InputStreamReader(gzis);
133. BufferedReader is = new BufferedReader(xover);
134. String line;
135. while ((line = is.readLine()) != null)
136. System.out.println("Read: " + line);
11. 目录和文件操作
Java代码
1. // 获取文件信息
2. exists(): 如 果文件存在，返回true
3. getCanonicalPath(): 获 取全名
4. getName(): 文件名
5. getParent(): 父 目录
6. canRead(): 如果文件可读，返回true
7. canWrite(): 如 果文件可写，返回true
8. lastModified(): 文 件更新时间
9. length(): 文件大小
10. isFile(): 如 果是文件，返回true
11. ifDirectory(): 如 果是目录，返回true
12. 要 调用文件的这些方法，必须
13. File f = new File(fileName);
14.
15. // 创建文件
16. File f = new File("c:\\test\\mytest.txt");
17. f.createNewFile(); // 创建mytest.txt文件到test目录下
18.
19. // 修改文件名
20. File f = new File("c:\\test\\mytest.txt");
21. f.renameTo(new File("c:\\test\\google.txt"));
22. 把 mytest.txt修改成google.txt
23.
24. // 删除文件
25. File f = new File("c:\\test\\mytest.txt");
26. f.delete();
27.
28. // 临时文件
29. File f = new File("C:\\test"); // 指定一个文件夹
30. // 在test文件夹中创建foo前缀，tmp后缀的临时文件
31. File tmp = File.createTempFile("foo", "tmp", f);
32. tmp.deleteOnExit(); // 在程序结束时删除该临时文件
33.
34. // 更改文件属性
35. setReadOnly(): 设 置为只读
36. setlastModified(): 设置最后更改时间
37.
38. // 列出当前文件夹的文件列表
39. String[] dir = new java.io.File(".").list();
40. java.util.Arrays.sort(dir);
41. for (int i = 0; i < dir.length; i++) {
42. System.out.println(dir);
43. }
44.
45. // 过滤文件列表
46. class OnlyJava implements FilenameFilter {
47. public boolean accept(File dir, String s) {
48. if (s.endsWith(".java") || s.endsWith(".class") || s.endsWith(".jar"))
49. return true;
50. }
51. }
52.
53. // 获取根目录
54. File[] rootDir = File.listRoots();
55. for (int i = 0; i < rootDir.length; i++) {
56. System.out.println(rootDir);
57. }
58.
59. // 创建新目录
60. new File("/home/ian/bin").mkdir(); // 如果"/home/ian"存在，则可以创建bin目录
61. 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
Java代码
1. // I18N资源
2. ResourceBundle rb = ResourceBundle.getBundle("Menus");
3. String label = rb.getString("exit.label");
4. // ResourceBundle相当于名值对，获取Menus按钮的区域属性
5. Menus_cn.properties: 不 同区域的属性文件
6.
7. // 列出有效区域
8. Locale[] list = Locale.getAvailableLocales()；
9.
10. // 指定区域
11. Locale cnLocale = Locale.CHINA;
12.
13. // 设置默认区域
14. Locale.setDefault(Locale.CHINA);
15.
16. // 格式化消息
17. public class MessageFormatDemo {
18. static Object[] data = {
19. new java.util.Date(),
20. "myfile.txt",
21. "could nto be opened"
22. };
23. public static void main(String[] args) {
24. String result = MessageFormat.format("At {0,time} on {0,date}, {1} {2}.", data);
25. System.out.println(result);
26. }
27. }
28. 输 出: At 10:10:08 on 2009-6-18, myfile.txt could nto be opened.
29.
30. // 从资源文件中读消息
31. Widgets.properties 在com.sean.cook.chap11下
32. ResourceBundle rb = ResourceBundle.getBundle("com.sean.cook.chap11.Widgets");
33. String propt = rb.getString("filedialogs.cantopen.string");
34. String result = MessageFormat.format(rb.getString("filedialogs.cantopen.format"), data);
13. 网络客户端
Java代码
1. // 访问服务器
2. Socket socket = new Socket("127.0.0.1", 8080);
3. // todo something
4. socket.close();
5.
6. // 查找网络地址
7. InetAddress.getByName(hostName).getHostAddress()); // 根据主机名得到IP地址
8. InetAddress.getByName(ipAddr).getHostName()); // 根据IP地址得到主机名
9.
10. // 连接具体异常
11. UnknownHostException
12. NoRouteToHostException
13. ConnectException
14.
15. // Socket读写文本数据
16. BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
17. String remoteTime = in.readline();
18. PrintWriter out = new PrintWriter(socket.getOutputStream(), true);
19. out.print("send message to client \r\n");
20. out.flush();
21.
22. // Socket读写二进制数据
23. DataInputStream in = new DataInputStream(new BufferedInputStream(socket.getInputStream()));
24. long remoteTime = (long)(in.readUnsignedByte() << 24);
25. DataOutputStream out = new DataOutputStream(socket.getOutputStream(), true);
26.
27. // Socket读写串行化数据
28. ObjectInputStream in = new ObjectInputStream(new BufferedInputStream(socket.getInputStream()));
29. Object o = in.readObject();
30. if (o instanceof Date) // 验证对象类型
31. ObjectOutputStream out = new ObjectOutputStream(socket.getOutputStream(), true);
32.
33. // UDP数据报
34. private final static int PACKET_SIZE = 1024;
35.
36. String host = "EV001B389673DE";
37. InetAddress serverAddr = InetAddress.getByName(host);
38. DatagramSocket socket = new DatagramSocket();
39. byte[] buffer = new byte[PACKET_SIZE]; // 分配数据缓冲空间
40. DatagramPacket packet = new DatagramPacket(buffer, PACKET_SIZE, serverAddr, 8080);
41. packet.setLength(PACKET_SIZE-1); // 设置数据长度
42. socket.send(packet);
43. socket.receive(packet); // 接收数据
14. 服务器端: Socket
Java代码
1. // 创建ServerSocket
2. ServerSocket serverSocket;
3. Socket clientSocket;
4.
5. serverSocket = new ServerSocket(9999);
6. while ((clientSocket = serverSocket.accept()) != null) {
7. System.out.println("Accept from client " + s.getInetAddress());
8. s.close();
9. }
10.
11. // 监听内部网
12. public static final short PORT = 9999;
13. public static final String INSIDE_HOST = "acmewidgets-inside"; // 网络接口名
14. public static final int BACKLOG = 10; // 待发数
15. serverSocket = new ServerSocket(PORT, BACKLOG, InetAddress.getByName(INSIDE_HOST));
16.
17. // 返回相应对象
18. ServerSocket serverSocket = new ServerSocket(9999);;
19. Socket clientSocket;
20. BufferedReader in = null;
21. PrintWriter out = null;
22. while (true) {
23. clientSocket = serverSocket.accept();
24. in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream(), "8859_1"));
25. out = new PrintWriter(new OutputStreamWriter(clientSocket.getOutputStream(), "8859_1"), true);
26. String echoLine;
27. while ((echoLine = in.readLine()) != null) {
28. System.out.println("Read " + echoLine);
29. out.print(echoLine + "\r\n");
30. }
31. }
32. 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
33.
34. // 处理多客户端
35. 需要 把接收数据的处理放入多线程中
36. public class EchoServerThreaded {
37. public static final int ECHOPORT = 7;
38. public static final int NUM_THREADS = 4;
39.
40. public static void main(String[] av) {
41. new EchoServerThreaded(ECHOPORT, NUM_THREADS);
42. }
43.
44. public EchoServerThreaded2(int port, int numThreads) {
45. ServerSocket servSock;
46. Socket clientSocket;
47. try {
48. servSock = new ServerSocket(ECHOPORT);
49. } catch(IOException e) {
50. throw new RuntimeException("Could not create ServerSocket " + e);
51. }
52. for (int i = 0; i < numThreads; i++) {
53. new Handler(servSock, i).start();
54. }
55. }
56. }
57. class Handler extends Thread {
58. ServerSocket servSock;
59. int threadNumber;
60.
61. Handler(ServerSocket s, int i) {
62. super();
63. servSock = s;
64. threadNumber = i;
65. setName("Thread " + threadNumber);
66. }
67.
68. public void run() {
69. while (true) {
70. try {
71. System.out.println(getName() + " waiting");
72. Socket clientSocket;
73. synchronized (servSock) {
74. clientSocket = servSock.accept();
75. }
76. System.out.println(getName() + " starting, IP=" + clientSocket.getInetAddress());
77. BufferedReader is = new BufferedReader(new InputStreamReader(
78. clientSocket.getInputStream()));
79. PrintStream os = new PrintStream(clientSocket.getOutputStream(), true);
80. String line;
81. while ((line = is.readLine()) != null) {
82. os.print(line + "\r\n");
83. os.flush();
84. }
85. System.out.println(getName() + " ENDED ");
86. clientSocket.close();
87. } catch (IOException ex) {
88. System.out.println(getName() + ": IO Error on socket " + ex);
89. return;
90. }
91. }
92. }
93. }
94.
95. // 使用SSL和JSSE保护Web服务器
96. SSLServerSocketFactory ssf = (SSLServerSocketFactory)SSLServerSocketFactory.getDefault()；
97. ServerSocket serverSocket = ssf.createServerSocket(8080);
98.
99. // Log4j
100. Level 级别: DEBUG < INFO < WARN < ERROR < FATAL < OFF
101. Appender: 输 出信息
102. ConsoleAppender: 输出控制台 System.out
103.
104. // 找到网络接口
105. Enumeration list = NetworkInterface.getNetworkInterfaces();
106. while (list.hasMoreElements()) {
107. NetworkInterface iface = (NetworkInterface)list.nextElement();
108. System.out.println(iface.getDisplayName());
109. Enumeration addrs = iface.getInetAddresses();
110. while (addrs.hasMoreElements()) {
111. InetAddress addr = (InetAddress)addrs.nextElement();
112. System.out.println(addr);
113. }
114. }
15. Java Mail
Java代码
1. // 发送Mail
2. protected String msgRecIp = "hxydream@163.com";
3. protected String msgSubject = "babytree";
4. protected String msgCc = "nobody@erewhon.com";
5. protected String msgBody = "test body";
6. protected Session session;
7. protected Message msg;
8.
9. public void doSend() {
10. // 创建属性文件
11. Properties props = new Properties();
12. props.put("mail.smtp.host", "mailhost");
13. // 创建Session对象
14. session = Session.getDefaultInstance(props, null);
15. session.setDebug(true);
16. msg = new MimeMessage(session); // 创建邮件
17. msg. setFrom(new InternetAddress("nobody@host.domain"));
18. InternetAddress toAddr = new InternetAddress(msgRecIp);
19. msg.addRecipient(Message.RecipientType.TO, toAddr);
20. InternetAddress ccAddr = new InternetAddress(msgCc);
21. msg.addRecipient(Message.RecipientType.CC, ccAddr);
22. msg.setSubject(msgSubject);
23. msg.setText(msgBody);
24. Transport.send(msg);
25. }
26.
27. // 发送MIME邮件
28. Multipart mp = new MimeMultipart();
29. BodyPart textPart = new MimeBodyPart();
30. textPart.setText(message_body); // 设置类型"text/plain"
31. BodyPart pixPart = new MimeBodyPart();
32. pixPart.setContent(html_data, "text/html");
33. mp.addBodyPart(textPart);
34. mp.addBodyPart(pixPart);
35. mesg.setContent(mp);
36. Transport.send(mesg);
37.
38. // 读Mail
39. Store store = session.getStore(protocol);
40. store.connect(host, user, password);
41. Folder rf;
42. rf = store.getFolder(root);
43. rf = store.getDefaultFolder();
44. rf.open(Folder.READ_WRITE);
16. 数据库访问
Java代码
1. // JDO
2. Properties p = new Properties();
3. p.load(new FileInputStream("jdo.properties"));
4. PersistenceManagerFactory pmf = JDOHelper.getPersistenceManagerFactory(p);
5. PersistenceManager pm = pmf.getPersistenceManager();
6. // 提交数据
7. pm.currentTransaction().begin();
8. if (o instanceof Collection) {
9. pm.makePersistentAll((Collection) o);
10. } else {
11. pm.makePersistent(o);
12. }
13. pm.currentTransaction().commit();
14. pm.close();
15. // 取出数据
16. Object[] data = new Object[3];
17. pm.retrieveAll(data);
18. for (int i = 0; i < data.length; i++) {
19. System.out.println(data);
20. }
21. pm.close();
22.
23. // 数据操作
24. Class clz = Class.forName("oracle.jdbc.driver.OracleDriver");
25. String dbUrl = "jdbc
racle:thin
192.168.0.23:1521#:nms";
26. Connection conn = DriverManager.getConnection(dbUrl, "su", "1234");
27. Statement stmt = conn.createStatement();
28. ResultSet rs = stmt.executeQuery("select * from pmtable");
29. while (rs.next()) {
30. String name = rs.getString(1);
31. String otherName = rs.getString("name");
32. }
33.
34. // 使用PreparedStatement提高性能，除了查询，都使用executeUpdate执行操作
35. PreparedStatement pstmt = conn.prepareStatement("select * from pmtable where name = ?");
36. pstmt.setString(1, "sean");
37. ResultSet rs = pstmt.executeQuery();
38.
39. // 调用存储过程
40. CallableStatement cs = conn.prepareCall("{ call ListDefunctUsers }");
41. ResultSet rs = cs.executeQuery();
42.
43. // 显示数据库表信息
44. DatabaseMetaData meta = conn.getMetaData();
45. meta.getDatabaseProductName();
46. meta.getDatabaseProductVersion();
47. 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
Java代码
1. // 从对象中生成XML
2. private final static String FILENAME = "serial.xml";
3. public static void main(String[] args) throws IOException {
4. String a = "hard work and best callback";
5. new SerialDemoXML().write(a);
6. new SerialDemoXML().dump();
7. }
8. public void write(Object obj) throws IOException {
9. XMLEncoder os = new XMLEncoder(new BufferedOutputStream(new FileOutputStream(FILENAME)));
10. os.writeObject(obj);
11. os.close();
12. }
13. public void dump() throws IOException {
14. XMLDecoder out = new XMLDecoder(new BufferedInputStream(new FileInputStream(FILENAME)));
15. System.out.println(out.readObject());
16. out.close();
17. }
18. serial.xml 格式内容如下:
19. <?xml version="1.0" encoding="UTF-8"?>
20. <java version="1.6.0_02" class="java.beans.XMLDecoder">
21. <string>hard work and best callback</string>
22. </java>
23. 控 制台输出
24. hard work and best callback
25.
26. // XSLT转换XML
27. XSLT 可以用来对输出格式进行各种控制
28. Transformer tx = TransformerFactory.newInstance().newTransformer(new StreamSource("people.xml"));
29. tx.transform(new StreamSource("people.xml"), new StreamResult("people.html"));
30.
31. // 用SAX解析XML - 主要用于查找关键元素，不用全文遍历
32. public SaxLister() throws SAXException, IOException {
33. XMLReader parser = XMLReaderFactory.createXMLReader("org.apache.xerces.parsers.SAXParser");
34. parser.setContentHandler(new PeopleHandler());
35. parser.parse("C:\\StudySource\\javacooksrc2\\xml\\people.xml");
36. }
37. class PeopleHandler extends DefaultHandler {
38. boolean parent = false;
39. boolean kids = false;
40. public void startElement(String nsURI, String localName, String rawName, Attributes attr) throws SAXException {
41. System.out.println("startElement: " + localName + "," + rawName);
42. if (rawName.equalsIgnoreCase("name"))
43. parent = true;
44. if (rawName.equalsIgnoreCase("children"))
45. kids = true;
46. }
47. public void characters(char[] ch, int start, int length) {
48. if (parent) {
49. System.out.println("arent: " + new String(ch, start, length));
50. parent = false;
51. } else if (kids) {
52. System.out.println("Children: " + new String(ch, start, length));
53. kids = false;
54. }
55. }
56. public PeopleHandler() throws SAXException {
57. super();
58. }
59. }
60.
61. // DOM解析XML - 遍历整个树
62. String uri = "file:" + new File("C:\\StudySource\\javacooksrc2\\xml\\people.xml").getAbsolutePath();
63. DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
64. DocumentBuilder builder = factory.newDocumentBuilder();
65. Document doc = builder.parse(uri);
66. NodeList nodes = doc.getChildNodes();
67. for (int i = 0; i < nodes.getLength(); i++) {
68. Node n = nodes.item(i);
69. switch (n.getNodeType()) {
70. case Node.ELEMENT_NODE:
71. // todo
72. break;
73. case Node.TEXT_NODE:
74. // todo
75. break;
76. }
77. }
78.
79. // 使用DTD或者XSD验证
80. 定 义好DTD或XSD文件
81. XmlDocument doc = XmlDocument.createXmlDocument(uri, true);
82.
83. // 用DOM生成XML
84. DocumentBuilderFactory fact = DocumentBuilderFactory.newInstance();
85. DocumentBuilder parser = fact.newDocumentBuilder();
86. Document doc = parser.newDocument();
87. Node root = doc.createElement("oem");
88. doc.appendChild(root);
89. Node stanza = doc.createElement("Stanza");
90. root.appendChild(stanza);
91. Node line = doc.createElement("Line");
92. stanza.appendChild(line);
93. line.appendChild(doc.createTextNode("Once, upon a midnight dreary"));
94. line = doc.createElement("Line");
95. stanza.appendChild(line);
96. line.appendChild(doc.createTextNode("While I pondered, weak and weary"));
18. RMI
Java代码
1. a. 定义 客户端与服务器之间的通信接口
2. public interface RemoteDate extends Remote {
3. public Date getRemoteDate() throws RemoteException;
4. public final static String LOOKUPNAME = "RemoteDate";
5. }
6.
7. b. 编 写RMI服务器
8. public class RemoteDateImpl extends UnicastRemoteObject implements RemoteDate {
9. public RemoteDateImpl() throws RemoteException {
10. super();
11. }
12. public Date getRemoteDate() throws RemoteException {
13. return new Date();
14. }
15. }
16. RemoteDateImpl im = new RemoteDateImpl();
17. System.out.println("DateServer starting...");
18. Naming.rebind(RemoteDate.LOOKUPNAME, im);
19. System.out.println("DateServer ready.");
20.
21. c. 运 行rmic生成stub
22. javac RemoteDateImpl.java
23. rmic RemoteDateImpl
24.
25. d. 编 写客户端
26. netConn = (RemoteDate)Naming.lookup(RemoteDate.LOOKUPNAME);
27. Date today = netConn.getRemoteDate();
28. System.out.println(today.toString());
29.
30. e. 确 保RMI注册表运行
31. rmiregistry
32.
33. f. 启 动服务器
34. java RemoteDateImpl
35.
36. g. 运 行客户端
37. 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
Java代码
1. // 停止线程 - 不要使用stop()方法
2. private boolean done = false;
3. public void run() {
4. while (!done) {
5. //todo
6. }
7. }
8. public void shutDown() {
9. done = true;
10. }
11. 可 以调用shutDown()方法来结束线程
12.
13. // 如果读取IO的时候出现堵塞，那么可以使用下面方法
14. public void shutDown() throws IOException {
15. if (io != null)
16. io.close();
17. }
18.
19. // 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
20. Thread t = new Thread() {
21. public void run() {
22. System.out.println("Reading");
23. try {
24. System.in.read();
25. } catch (IOException e) {
26. System.err.println(e);
27. }
28. System.out.println("Thread finished.");
29. }
30. };
31. System.out.println("Starting");
32. t.start();
33. System.out.println("Joining");
34. try {
35. t.join();
36. } catch (InterruptedException e) {
37. System.out.println("Who dares imterrupt my sleep?");
38. }
39. System.out.println("Main finished.");
40.
41. // 加锁保证同步
42. Lock lock = new ReentrantLock();
43. try {
44. lock.lock();
45. // todo
46. } finally {
47. lock.unlock();
48. }
49.
50. 线 程通信wait(), notify(), notifyAll()
51. 生产者-消费者模式
52. Executors
21. 内省或“命令类的类”
Java代码
1. // 反射
2. Class c = Class.forName("java.lang.String");
3. Constructor[] cons = c.getConstructors();
4. for (int i = 0; i < cons.length; i++) {
5. System.out.println(cons.toString());
6. }
7. Method[] meths = c.getMethods();
8. for (int i = 0; i < meths.length; i++) {
9. System.out.println(meths.toString());
10. }
11.
12. // 动态装载类
13. Class c = Class.forName("java.lang.String");
14. Object obj = c.newInstance();
15.
16. // 通过反射调用类的方法
17. class X {
18. public void master(String s) {
19. System.out.println("Working on \"" + s + "\"");
20. }
21. }
22. Class clx = X.class;
23. Class[] argTypes = {String.class};
24. Method worker = clx.getMethod("master", argTypes);
25. Object[] theData = {"Chocolate chips"};
26. worker.invoke(new X(), theData);
27. 输 出: Working on "Chocolate chips"
22. Java与其他语言的结合
Java代码
1. // 执行CMD命令，在Eclipse控制台输出
2. Process p = Runtime.getRuntime().exec("C:/StudySource/ver.cmd");
3. p.waitFor(); // 等待命令执行完
4. BufferedReader br = new BufferedReader(new InputStreamReader(p.getInputStream()));
5. String s;
6. while ((s = br.readLine()) != null)
7. System.out.println(s);
8.
9. // 调用Jython - 计算22.0/7
10. BSFManager manager = new BSFManager();
11. String[] fntypes = {".py"};
12. manager.registerScriptingEngine("jython", "org.apache.bsf.engines.jython.JythonEngine", fntypes);
13. Object r = manager.eval("jython", "testString", 0, 0, "22.0/7");
14. System.out.println("Result type is " + r.getClass().getName());
15. System.out.println("Result value is " + r);
