上次编译的 Java 打印时间

Question

我希望嵌入一段代码，该代码将打印出当前类最后一次编译的时间。这如何在 Java 中实现？

Answer 1

这个问题很久以前就有答案了。但万一有人经过这里有一个适合我的解决方案，类似于 Supah Fly 的建议，但支持 jar 和文件。

private long classBuildTimeMillis() throws URISyntaxException, IllegalStateException, IllegalArgumentException {
    URL resource = getClass().getResource(getClass().getSimpleName() + ".class");
    if (resource == null) {
        throw new IllegalStateException("Failed to find class file for class: " + 
                                        getClass().getName());
    }

    if (resource.getProtocol().equals("file")) {

        return new File(resource.toURI()).lastModified();

    } else if (resource.getProtocol().equals("jar")) {

        String path = resource.getPath();
        return new File(path.substring(5, path.indexOf("!"))).lastModified();

    } else {

        throw new IllegalArgumentException("Unhandled url protocol: " + 
                resource.getProtocol() + " for class: " +
                getClass().getName() + " resource: " + resource.toString());
    }
}

但这不会处理 zip 文件或静态上下文，并且如果事情不顺利，它会抛出异常而不是返回 null。这个比较友好一点:

private static final Date buildDate = getClassBuildTime();

/**
 * Handles files, jar entries, and deployed jar entries in a zip file (EAR).
 * @return The date if it can be determined, or null if not.
 */
private static Date getClassBuildTime() {
    Date d = null;
    Class<?> currentClass = new Object() {}.getClass().getEnclosingClass();
    URL resource = currentClass.getResource(currentClass.getSimpleName() + ".class");
    if (resource != null) {
        if (resource.getProtocol().equals("file")) {
            try {
                d = new Date(new File(resource.toURI()).lastModified());
            } catch (URISyntaxException ignored) { }
        } else if (resource.getProtocol().equals("jar")) {
            String path = resource.getPath();
            d = new Date( new File(path.substring(5, path.indexOf("!"))).lastModified() );    
        } else if (resource.getProtocol().equals("zip")) {
            String path = resource.getPath();
            File jarFileOnDisk = new File(path.substring(0, path.indexOf("!")));
            //long jfodLastModifiedLong = jarFileOnDisk.lastModified ();
            //Date jfodLasModifiedDate = new Date(jfodLastModifiedLong);
            try(JarFile jf = new JarFile (jarFileOnDisk)) {
                ZipEntry ze = jf.getEntry (path.substring(path.indexOf("!") + 2));//Skip the ! and the /
                long zeTimeLong = ze.getTime ();
                Date zeTimeDate = new Date(zeTimeLong);
                d = zeTimeDate;
            } catch (IOException|RuntimeException ignored) { }
        }
    }
    return d;
}