20非常有用的Java程序片段(3)

15. 创建ZIP和JAR文件

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 stream   
            bis = 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. 解析/读取XML 文件

XML文件

<?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代码：

ackage 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");   
    }   
}