20个开发人员十分有用的Java功能代码

2012-07-08

20个开发人员非常有用的Java功能代码1. 把Strings转换成int和把int转换成String 5. 通过Java JDBC链接Orac

20个开发人员非常有用的Java功能代码

1. 把Strings转换成int和把int转换成String

5. 通过Java JDBC链接Oracle数据库

public class OracleJdbcTest??{??String driverClass = "oracle.jdbc.driver.OracleDriver";??Connection con;??public void init(FileInputStream fs) throws ClassNotFoundException,?
SQLException, FileNotFoundException, IOException??{??Properties props = new Properties();??props.load(fs);??String url = props.getProperty("db.url");??String userName = props.getProperty("db.user");??String password = props.getProperty("db.password");??Class.forName(driverClass);??con=DriverManager.getConnection(url, userName, password);??}??public void fetch() throws SQLException, IOException??{??PreparedStatement ps = con.prepareStatement("select SYSDATE from dual");??ResultSet rs = ps.executeQuery();??while (rs.next())??{??// do the thing you do??}??rs.close();??ps.close();??}??public static void main(String[] args)??{??OracleJdbcTest test = new OracleJdbcTest();??test.init();??test.fetch();??}??}?
public class OracleJdbcTest{String driverClass = "oracle.jdbc.driver.OracleDriver";
Connection con;
public void init(FileInputStream fs) throws ClassNotFoundException,
SQLException, FileNotFoundException, IOException{Properties props = new Properties();props.load(fs);String url = props.getProperty("db.url");String userName = props.getProperty("db.user");String password = props.getProperty("db.password");Class.forName(driverClass);
con=DriverManager.getConnection(url, userName, password);}
public void fetch() throws SQLException, IOException{PreparedStatement ps = con.prepareStatement("select SYSDATE from
dual");ResultSet rs = ps.executeQuery();
while (rs.next()){// do the thing you do}rs.close();ps.close();}
public static void main(String[] args){OracleJdbcTest test = new OracleJdbcTest();test.init();test.fetch();}}

6.将Java中的util.Date转换成sql.Date

这一片段显示如何将一个java util Date转换成sql Date用于数据库

import java.util.zip.*;import java.io.*;

public class ZipIt {public static void main(String args[]) throws IOException {if (args.length < 2) {System.err.println("usage: java ZipIt Zip.zip file1 file2 file3");System.exit(-1);}File zipFile = new File(args[0]);if (zipFile.exists()) {System.err.println("Zip file already exists, please try another");System.exit(-2);}FileOutputStream fos = new FileOutputStream(zipFile);ZipOutputStream zos = new ZipOutputStream(fos);int bytesRead;byte[] buffer = new byte[1024];CRC32 crc = new CRC32();for (int i=1, n=args.length; i < n; i++) {String name = args[i];File file = new File(name);if (!file.exists()) {?? System.err.println("Skipping: " + name); ?? continue;}BufferedInputStream bis = new BufferedInputStream(?? new FileInputStream(file));crc.reset();while ((bytesRead = bis.read(buffer)) != -1) {?? crc.update(buffer, 0, bytesRead);}bis.close();// Reset to beginning of input streambis = new BufferedInputStream(?? new FileInputStream(file));ZipEntry entry = new ZipEntry(name);entry.setMethod(ZipEntry.STORED);  entry.setCompressedSize(file.length());entry.setSize(file.length());entry.setCrc(crc.getValue());zos.putNextEntry(entry);while ((bytesRead = bis.read(buffer)) != -1) {?? zos.write(buffer, 0, bytesRead);}bis.close();}zos.close();}}16. Parsing / Reading XML file in JavaSample XML file.

???John?B?12???Mary?A?11???Simon?A?18???

JohnB12MaryA<AGE>11SimonA18Java code to parse above XML.

package net.viralpatel.java.xmlparser;??import java.io.File;??import javax.xml.parsers.DocumentBuilder;??import javax.xml.parsers.DocumentBuilderFactory;??import org.w3c.dom.Document;??import org.w3c.dom.Element;??import org.w3c.dom.Node;??import org.w3c.dom.NodeList;??public class XMLParser {??public void getAllUserNames(String fileName) {??try {??DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();??DocumentBuilder db = dbf.newDocumentBuilder();??File file = new File(fileName);??if (file.exists()) {?? ? Document doc = db.parse(file);?? ? Element docEle = doc.getDocumentElement();?? ? // Print root element of the document?? ? System.out.println("Root element of the document: "? ????????? + docEle.getNodeName());?? ? NodeList studentList = docEle.getElementsByTagName("student");?? ? // Print total student elements in document?? ? System.out?? ????????? .println("Total students: " + studentList.getLength());?? ? if (studentList != null && studentList.getLength() > 0) {?? ????? for (int i = 0; i < studentList.getLength(); i++) {?? ????????? Node node = studentList.item(i);?? ????????? if (node.getNodeType() == Node.ELEMENT_NODE) {?? ????????????? System.out?? ????????????????????? .println("=====================");?? ????????????? Element e = (Element) node;?? ????????????? NodeList nodeList = e.getElementsByTagName("name");?? ????????????? System.out.println("Name: "? ????????????????????? + nodeList.item(0).getChildNodes().item(0)?? ???????????????????????????;?? .getNodeValue());?? ????????????? nodeList = e.getElementsByTagName("grade");?? ????????????? System.out.println("Grade: "? ????????????????????? + nodeList.item(0).getChildNodes().item(0)?? ???????????????????????????;?? .getNodeValue());?? ????????????? nodeList = e.getElementsByTagName("age");?? ????????????? System.out.println("Age: "? ????????????????????? + nodeList.item(0).getChildNodes().item(0)?? ???????????????????????????;?? .getNodeValue());?? ????????? }?? ????? }?? ? } else {?? ????? System.exit(1);?? ? }??}??} catch (Exception e) {??System.out.println(e);??}??}??public static void main(String[] args) {??XMLParser parser = new XMLParser();??parser.getAllUserNames("c:\\test.xml");??}??}?

package net.viralpatel.java.xmlparser;

import java.io.File;import javax.xml.parsers.DocumentBuilder;import javax.xml.parsers.DocumentBuilderFactory;

import org.w3c.dom.Document;import org.w3c.dom.Element;import org.w3c.dom.Node;import org.w3c.dom.NodeList;

public class XMLParser {

public void getAllUserNames(String fileName) {try {DocumentBuilderFactory dbf =

DocumentBuilderFactory.newInstance();DocumentBuilder db = dbf.newDocumentBuilder();File file = new File(fileName);if (file.exists()) {Document doc = db.parse(file);Element docEle = doc.getDocumentElement();

// Print root element of the documentSystem.out.println("Root element of the document: "+ docEle.getNodeName());

NodeList studentList = docEle.getElementsByTagName

("student");

// Print total student elements in documentSystem.out .println("Total students: " +

studentList.getLength());

if (studentList != null && studentList.getLength()

> 0) {for (int i = 0; i < studentList.getLength

(); i++) {

Node node = studentList.item(i);

if (node.getNodeType() ==

Node.ELEMENT_NODE) {

System.out?????.println

("=====================");

Element e = (Element) node;NodeList nodeList =

e.getElementsByTagName("name");System.out.println("Name: "+

nodeList.item(0).getChildNodes().item(0)

.getNodeValue());

nodeList =

e.getElementsByTagName("grade");System.out.println("Grade:

nodeList.item(0).getChildNodes().item(0)

.getNodeValue());

nodeList =

e.getElementsByTagName("age");System.out.println("Age: "+

nodeList.item(0).getChildNodes().item(0)

.getNodeValue());}}} else {System.exit(1);}}} catch (Exception e) {System.out.println(e);}}public static void main(String[] args) {

XMLParser parser = new XMLParser();parser.getAllUserNames("c:\\test.xml");}}17. Convert Array to Map in Java

import java.util.Map;??import org.apache.commons.lang.ArrayUtils;??public class Main {??public static void main(String[] args) {??String[][] countries = { { "United States", "New York" }, { "United Kingdom",

"London" },??{ "Netherland", "Amsterdam" }, { "Japan", "Tokyo" }, { "France", "Paris" }

};??Map countryCapitals = ArrayUtils.toMap(countries);??System.out.println("Capital of Japan is " + countryCapitals.get("Japan"));??System.out.println("Capital of France is " + countryCapitals.get("France"));??}??}?

import java.util.Map;import org.apache.commons.lang.ArrayUtils;

public class Main {

public static void main(String[] args) {String[][] countries = { { "United States", "New York" }, { "United Kingdom",

"London" },{ "Netherland", "Amsterdam" }, { "Japan", "Tokyo" }, { "France", "Paris" }

};

Map countryCapitals = ArrayUtils.toMap(countries);

System.out.println("Capital of Japan is " + countryCapitals.get("Japan"));System.out.println("Capital of France is " + countryCapitals.get("France"));}}18. Send Email using Java

import javax.mail.*;??import javax.mail.internet.*;??import java.util.*;??public void postMail( String recipients[ ], String subject, String message , String

from) throws MessagingException??{??boolean debug = false;??//Set the host smtp address??Properties props = new Properties();??props.put("mail.smtp.host", "smtp.example.com");??// create some properties and get the default Session??Session session = Session.getDefaultInstance(props, null);??session.setDebug(debug);??// create a message??Message msg = new MimeMessage(session);??// set the from and to address??InternetAddress addressFrom = new InternetAddress(from);??msg.setFrom(addressFrom);??InternetAddress[] addressTo = new InternetAddress[recipients.length];??for (int i = 0; i < recipients.length; i++)??{??addressTo[i] = new InternetAddress(recipients[i]);??}??msg.setRecipients(Message.RecipientType.TO, addressTo);??// Optional : You can also set your custom headers in the Email if you Want??msg.addHeader("MyHeaderName", "myHeaderValue");??// Setting the Subject and Content Type??msg.setSubject(subject);??msg.setContent(message, "text/plain");??Transport.send(msg);??}?

import javax.mail.*;import javax.mail.internet.*;import java.util.*;

public void postMail( String recipients[ ], String subject, String message , String

from) throws MessagingException{boolean debug = false;

//Set the host smtp addressProperties props = new Properties();props.put("mail.smtp.host", "smtp.example.com");

// create some properties and get the default SessionSession session = Session.getDefaultInstance(props, null);session.setDebug(debug);

// create a messageMessage msg = new MimeMessage(session);

// set the from and to addressInternetAddress addressFrom = new InternetAddress(from);msg.setFrom(addressFrom);

InternetAddress[] addressTo = new InternetAddress[recipients.length];for (int i = 0; i < recipients.length; i++){addressTo[i] = new InternetAddress(recipients[i]);}msg.setRecipients(Message.RecipientType.TO, addressTo);

// Optional : You can also set your custom headers in the Email if you Wantmsg.addHeader("MyHeaderName", "myHeaderValue");

// Setting the Subject and Content Typemsg.setSubject(subject);msg.setContent(message, "text/plain");Transport.send(msg);}19. Send HTTP request & fetching data using Java

import java.io.BufferedReader;??import java.io.InputStreamReader;??import java.net.URL;??public class Main {??public static void main(String[] args)? {??try {??URL my_url = new URL("http://www.viralpatel.net/blogs/"); ?BufferedReader br = new BufferedReader(new InputStreamReader

(my_url.openStream()));??String strTemp = "";??while(null != (strTemp = br.readLine())){??System.out.println(strTemp);??}??} catch (Exception ex) {??ex.printStackTrace();??}??}??}?

import java.io.BufferedReader;import java.io.InputStreamReader;import java.net.URL;

public class Main {public static void main(String[] args)? {try {URL my_url = new URL("http://www.viralpatel.net/blogs/");???BufferedReader br = new BufferedReader(new

InputStreamReader(my_url.openStream()));String strTemp = "";while(null != (strTemp = br.readLine())){System.out.println(strTemp);}} catch (Exception ex) {ex.printStackTrace();}}}20. Resize an Array in Java

/**?* Reallocates an array with a new size, and copies the contents?* of the old array to the new array.?* @param oldArray? the old array, to be reallocated.?* @param newSize?? the new array size.?* @return????????? A new array with the same contents.?*/?private static Object resizeArray (Object oldArray, int newSize) {??int ldSize = java.lang.reflect.Array.getLength(oldArray);??Class elementType = oldArray.getClass().getComponentType();??Object newArray = java.lang.reflect.Array.newInstance(??elementType,newSize);??int preserveLength = Math.min(oldSize,newSize);??if (preserveLength > 0)??System.arraycopy (oldArray,0,newArray,0,preserveLength);??return newArray;??}??// Test routine for resizeArray().??public static void main (String[] args) {??int[] a = {1,2,3};??a = (int[])resizeArray(a,5);??a[3] = 4;??a[4] = 5;??for (int i=0; i????? System.out.println (a[i]);??}?

16. 在Java中解析/读取XML文件

view plaincopy to clipboardprint?<?xml version="1.0"?>?<students>?<student>?<name>John</name>?<grade>B</grade>?<age>12</age>?</student>?<student>?<name>Mary</name>?<grade>A</grade>?<age>11</age>?</student>?<student>?<name>Simon</name>?<grade>A</grade>?<age>18</age>?</student>?</students>??
<?xml version="1.0"?><students><student><name>John</name><grade>B</grade><age>12</age></student><student><name>Mary</name><grade>A</grade><age>11</age></student><student><name>Simon</name><grade>A</grade><age>18</age></student></students>Java code to parse above XML.
view plaincopy to clipboardprint?package net.viralpatel.java.xmlparser;??import java.io.File;??import javax.xml.parsers.DocumentBuilder;??import javax.xml.parsers.DocumentBuilderFactory;??import org.w3c.dom.Document;??import org.w3c.dom.Element;??import org.w3c.dom.Node;??import org.w3c.dom.NodeList;??public class XMLParser {??public void getAllUserNames(String fileName) {??try {??DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();??DocumentBuilder db = dbf.newDocumentBuilder();??File file = new File(fileName);??if (file.exists()) {??Document doc = db.parse(file);??Element docEle = doc.getDocumentElement();??// Print root element of the document??System.out.println("Root element of the document: "?+ docEle.getNodeName());??NodeList studentList = docEle.getElementsByTagName("student");??// Print total student elements in document??System.out??.println("Total students: " + studentList.getLength());??if (studentList != null && studentList.getLength() > 0) {??for (int i = 0; i < studentList.getLength(); i++) {??Node node = studentList.item(i);??if (node.getNodeType() == Node.ELEMENT_NODE) {??System.out??.println("=====================");??Element e = (Element) node;??NodeList nodeList = e.getElementsByTagName("name");??System.out.println("Name: "?+ nodeList.item(0).getChildNodes().item(0)??.getNodeValue());??nodeList = e.getElementsByTagName("grade");??System.out.println("Grade: "?+ nodeList.item(0).getChildNodes().item(0)??.getNodeValue());??nodeList = e.getElementsByTagName("age");??System.out.println("Age: "?+ nodeList.item(0).getChildNodes().item(0)??.getNodeValue());??}??}??} else {??System.exit(1);??}??}??} catch (Exception e) {??System.out.println(e);??}??}??public static void main(String[] args) {??XMLParser parser = new XMLParser();??parser.getAllUserNames("c:\\test.xml");??}??}?
package net.viralpatel.java.xmlparser;
import java.io.File;import javax.xml.parsers.DocumentBuilder;import javax.xml.parsers.DocumentBuilderFactory;
import org.w3c.dom.Document;import org.w3c.dom.Element;import org.w3c.dom.Node;import org.w3c.dom.NodeList;
public class XMLParser {
public void getAllUserNames(String fileName) {try {DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();DocumentBuilder db = dbf.newDocumentBuilder();File file = new File(fileName);if (file.exists()) {Document doc = db.parse(file);Element docEle = doc.getDocumentElement();
// Print root element of the documentSystem.out.println("Root element of the document: "+ docEle.getNodeName());
NodeList studentList = docEle.getElementsByTagName("student");
// Print total student elements in documentSystem.out.println("Total students: " + studentList.getLength());
if (studentList != null && studentList.getLength() > 0) {for (int i = 0; i < studentList.getLength(); i++) {
Node node = studentList.item(i);
if (node.getNodeType() == Node.ELEMENT_NODE) {
System.out.println("=====================");
Element e = (Element) node;NodeList nodeList = e.getElementsByTagName("name");System.out.println("Name: "+ nodeList.item(0).getChildNodes().item(0).getNodeValue());
nodeList = e.getElementsByTagName("grade");System.out.println("Grade: "+ nodeList.item(0).getChildNodes().item(0).getNodeValue());
nodeList = e.getElementsByTagName("age");System.out.println("Age: "+ nodeList.item(0).getChildNodes().item(0).getNodeValue());}}} else {System.exit(1);}}} catch (Exception e) {System.out.println(e);}}public static void main(String[] args) {
XMLParser parser = new XMLParser();parser.getAllUserNames("c:\\test.xml");}}

17. 在Java中将Array转换成Map

view plaincopy to clipboardprint?import java.util.Map;??import org.apache.commons.lang.ArrayUtils;??public class Main {??public static void main(String[] args) {??String[][] countries = { { "United States", "New York" }, { "United Kingdom", "London" },??{ "Netherland", "Amsterdam" }, { "Japan", "Tokyo" }, { "France", "Paris" } };??Map countryCapitals = ArrayUtils.toMap(countries);??System.out.println("Capital of Japan is " + countryCapitals.get("Japan"));??System.out.println("Capital of France is " + countryCapitals.get("France"));??}??}??
import java.util.Map;import org.apache.commons.lang.ArrayUtils;
public class Main {
public static void main(String[] args) {String[][] countries = { { "United States", "New York" }, { "United Kingdom", "London" },{ "Netherland", "Amsterdam" }, { "Japan", "Tokyo" }, { "France", "Paris" } };
Map countryCapitals = ArrayUtils.toMap(countries);
System.out.println("Capital of Japan is " + countryCapitals.get("Japan"));System.out.println("Capital of France is " + countryCapitals.get("France"));}}

18. 在Java中发送电子邮件

view plaincopy to clipboardprint?import javax.mail.*;??import javax.mail.internet.*;??import java.util.*;??public void postMail( String recipients[ ], String subject, String message , String from) throws MessagingException??{??boolean debug = false;??//Set the host smtp address??Properties props = new Properties();??props.put("mail.smtp.host", "smtp.example.com");??// create some properties and get the default Session??Session session = Session.getDefaultInstance(props, null);??session.setDebug(debug);??// create a message??Message msg = new MimeMessage(session);??// set the from and to address??InternetAddress addressFrom = new InternetAddress(from);??msg.setFrom(addressFrom);??InternetAddress[] addressTo = new InternetAddress[recipients.length];??for (int i = 0; i < recipients.length; i++)??{??addressTo[i] = new InternetAddress(recipients[i]);??}??msg.setRecipients(Message.RecipientType.TO, addressTo);??// Optional : You can also set your custom headers in the Email if you Want??msg.addHeader("MyHeaderName", "myHeaderValue");??// Setting the Subject and Content Type??msg.setSubject(subject);??msg.setContent(message, "text/plain");??Transport.send(msg);??}??
import javax.mail.*;import javax.mail.internet.*;import java.util.*;
public void postMail( String recipients[ ], String subject, String message , String from) throws MessagingException{boolean debug = false;
//Set the host smtp addressProperties props = new Properties();props.put("mail.smtp.host", "smtp.example.com");
// create some properties and get the default SessionSession session = Session.getDefaultInstance(props, null);session.setDebug(debug);
// create a messageMessage msg = new MimeMessage(session);
// set the from and to addressInternetAddress addressFrom = new InternetAddress(from);msg.setFrom(addressFrom);
InternetAddress[] addressTo = new InternetAddress[recipients.length];for (int i = 0; i < recipients.length; i++){addressTo[i] = new InternetAddress(recipients[i]);}msg.setRecipients(Message.RecipientType.TO, addressTo);
// Optional : You can also set your custom headers in the Email if you Wantmsg.addHeader("MyHeaderName", "myHeaderValue");
// Setting the Subject and Content Typemsg.setSubject(subject);msg.setContent(message, "text/plain");Transport.send(msg);}

19. 使用Java发送HTTP请求和提取数据

view plaincopy to clipboardprint?import java.io.BufferedReader;??import java.io.InputStreamReader;??import java.net.URL;??public class Main {??public static void main(String[] args)? {??try {??URL my_url = new URL("http://www.viralpatel.net/blogs/");??BufferedReader br = new BufferedReader(new InputStreamReader(my_url.openStream()));??String strTemp = "";??while(null != (strTemp = br.readLine())){??System.out.println(strTemp);??}??} catch (Exception ex) {??ex.printStackTrace();??}??}??}??
import java.io.BufferedReader;import java.io.InputStreamReader;import java.net.URL;
public class Main {public static void main(String[] args)? {try {URL my_url = new URL("http://www.viralpatel.net/blogs/");BufferedReader br = new BufferedReader(new InputStreamReader(my_url.openStream()));String strTemp = "";while(null != (strTemp = br.readLine())){System.out.println(strTemp);}} catch (Exception ex) {ex.printStackTrace();}}}

20. 在Java中调整数组

view plaincopy to clipboardprint?/**?* Reallocates an array with a new size, and copies the contents?* of the old array to the new array.?* @param oldArray? the old array, to be reallocated.?* @param newSize?? the new array size.?* @return????????? A new array with the same contents.?*/?private static Object resizeArray (Object oldArray, int newSize) {??int ldSize = java.lang.reflect.Array.getLength(oldArray);??Class elementType = oldArray.getClass().getComponentType();??Object newArray = java.lang.reflect.Array.newInstance(??elementType,newSize);??int preserveLength = Math.min(oldSize,newSize);??if (preserveLength > 0)??System.arraycopy (oldArray,0,newArray,0,preserveLength);??return newArray;??}??// Test routine for resizeArray().??public static void main (String[] args) {??int[] a = {1,2,3};??a = (int[])resizeArray(a,5);??a[3] = 4;??a[4] = 5;??for (int i=0; i<a.length; i++)??System.out.println (a[i]);??}?

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20个开发人员十分有用的Java功能代码