Java：在运行时将类添加到Jar存档

我想在运行时将一些编译类（.class文件）添加到当前Jar文件中的目录（包）
我怎样才能做到这一点？

谢谢

Answer 1

这是不可能的 – 要更新Jar文件，您需要创建一个新文件并用新文件覆盖旧文件。

以下是如何执行此操作的示例：

import java.io.*; import java.util.*; import java.util.zip.*; import java.util.jar.*; public class JarUpdate { /** * main() */ public static void main(String[] args) throws IOException { // Get the jar name and entry name from the command-line. String jarName = args[0]; String fileName = args[1]; // Create file descriptors for the jar and a temp jar. File jarFile = new File(jarName); File tempJarFile = new File(jarName + ".tmp"); // Open the jar file. JarFile jar = new JarFile(jarFile); System.out.println(jarName + " opened."); // Initialize a flag that will indicate that the jar was updated. boolean jarUpdated = false; try { // Create a temp jar file with no manifest. (The manifest will // be copied when the entries are copied.) Manifest jarManifest = jar.getManifest(); JarOutputStream tempJar = new JarOutputStream(new FileOutputStream(tempJarFile)); // Allocate a buffer for reading entry data. byte[] buffer = new byte[1024]; int bytesRead; try { // Open the given file. FileInputStream file = new FileInputStream(fileName); try { // Create a jar entry and add it to the temp jar. JarEntry entry = new JarEntry(fileName); tempJar.putNextEntry(entry); // Read the file and write it to the jar. while ((bytesRead = file.read(buffer)) != -1) { tempJar.write(buffer, 0, bytesRead); } System.out.println(entry.getName() + " added."); } finally { file.close(); } // Loop through the jar entries and add them to the temp jar, // skipping the entry that was added to the temp jar already. for (Enumeration entries = jar.entries(); entries.hasMoreElements(); ) { // Get the next entry. JarEntry entry = (JarEntry) entries.nextElement(); // If the entry has not been added already, add it. if (! entry.getName().equals(fileName)) { // Get an input stream for the entry. InputStream entryStream = jar.getInputStream(entry); // Read the entry and write it to the temp jar. tempJar.putNextEntry(entry); while ((bytesRead = entryStream.read(buffer)) != -1) { tempJar.write(buffer, 0, bytesRead); } } } jarUpdated = true; } catch (Exception ex) { System.out.println(ex); // Add a stub entry here, so that the jar will close without an // exception. tempJar.putNextEntry(new JarEntry("stub")); } finally { tempJar.close(); } } finally { jar.close(); System.out.println(jarName + " closed."); // If the jar was not updated, delete the temp jar file. if (! jarUpdated) { tempJarFile.delete(); } } // If the jar was updated, delete the original jar file and rename the // temp jar file to the original name. if (jarUpdated) { jarFile.delete(); tempJarFile.renameTo(jarFile); System.out.println(jarName + " updated."); } } } 

Answer 2

我不太确定，但我不认为可以从JAR文件加载类（让我们称之为foo.jar），然后修改加载类的相同JAR文件，添加一个新类并期望ClassLoader找到的类。

我想考虑重构应用程序本身并使其能够动态加载类（使用URLClassLoader或任何其他技术），而不是试图强制您描述的单个JAR行为。