干货来啦！JAVA常用代码（二）

//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.chap11.Widgets");

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