java类加载器和运行时编译
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10-07-2019 - |
题
尽管警告会放弃目前的行动方案,但我目前看不到更好的方法来解决我的问题。我必须 在运行时生成 Java代码,然后编译,加载并引用它。
问题是生成的代码导入了系统类加载器已经加载的代码(我想) - 也就是代码路径中的一个jar中存在的代码。 (我在Java 6上运行Tomcat 6 Web容器。)你可能会问自己为什么这是一个问题 - 好吧我肯定不知道 - 但事实是我得到了编译错误:
/ W:/.../解析器/ V0.5 / AssignELParser.java:6: 包com.xxx.yyy.zzz.configuration 不存在
通过互联网上的一些例子,我定义了以下类:
class MemoryClassLoader extends ChainedAction {
private static final Logger LOG = Logger.getLogger(MemoryClassLoader.class);
private LoaderImpl impl;
private class LoaderImpl extends ClassLoader {
// The compiler tool
private final JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
// Compiler options
private final Iterable<String> options = Arrays.asList("-verbose");
// DiagnosticCollector, for collecting compilation problems
private final DiagnosticCollector<JavaFileObject> diagnostics = new DiagnosticCollector<JavaFileObject>();
// Our FileManager
private final MemoryFileManager manager = new MemoryFileManager(this.compiler);
public LoaderImpl(File sourceDirectory) {
List<Source> list = new ArrayList<Source>();
File[] files = sourceDirectory.listFiles(new FilenameFilter() {
@Override
public boolean accept(File dir, String name) {
return name.endsWith(Kind.SOURCE.extension);
}
});
for (File file : files) {
list.add(new Source(file));
}
CompilationTask task = compiler.getTask(null, manager, diagnostics, options, null, list);
Boolean compilationSuccessful = task.call();
LOG.info("Compilation has " + ((compilationSuccessful) ? "concluded successfully" : "failed"));
// report on all errors to screen
for (Diagnostic<? extends JavaFileObject> diagnostic : diagnostics.getDiagnostics()) {
LOG.warn(diagnostic.getMessage(null));
}
}
@Override
protected Class<?> findClass(String name) throws ClassNotFoundException {
synchronized (this.manager) {
Output output = manager.map.remove(name);
if (output != null) {
byte[] array = output.toByteArray();
return defineClass(name, array, 0, array.length);
}
}
return super.findClass(name);
}
}
@Override
protected void run() {
impl = new LoaderImpl(new File(/* Some directory path */));
}
}
class MemoryFileManager extends ForwardingJavaFileManager<JavaFileManager> {
final Map<String, Output> map = new HashMap<String, Output>();
MemoryFileManager(JavaCompiler compiler) {
super(compiler.getStandardFileManager(null, null, null));
}
@Override
public Output getJavaFileForOutput(Location location, String name, Kind kind, FileObject source) {
Output output = new Output(name, kind);
map.put(name, output);
return output;
}
}
class Output extends SimpleJavaFileObject {
private final ByteArrayOutputStream baos = new ByteArrayOutputStream();
Output(String name, Kind kind) {
super(URI.create("memo:///" + name.replace('.', '/') + kind.extension), kind);
}
byte[] toByteArray() {
return this.baos.toByteArray();
}
@Override
public ByteArrayOutputStream openOutputStream() {
return this.baos;
}
}
class Source extends SimpleJavaFileObject {
public Source(File file) {
super(file.toURI(), Kind.SOURCE);
}
@Override
public CharSequence getCharContent(boolean ignoreEncodingErrors) {
StringBuilder sb = new StringBuilder("");
try {
File file = new File(uri);
FileReader fr = new FileReader(file);
BufferedReader br = new BufferedReader(fr);
sb = new StringBuilder((int) file.length());
String line = "";
while ((line = br.readLine()) != null) {
sb.append(line);
sb.append("\n");
}
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return sb.toString();
}
}
通过扩展ClassLoader类并且不调用显式超级构造函数,内部类LoaderImpl似乎应该引用系统类加载器作为其父类加载器。
如果是这样,那为什么我得到<!> quot; runtime <!>;编译错误 - 上面?为什么找不到导入类的代码?
解决方案
不确定它是否有帮助,但您是否尝试明确指定类路径?
getClassPath()
{
ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
URL[] urls = ((URLClassLoader) classLoader).getURLs();
StringBuilder buf = new StringBuilder(1000);
buf.append(".");
String separator = System.getProperty("path.separator");
for (URL url : urls) {
buf.append(separator).append(url.getFile());
}
}
classPath = buf.toString();
然后
options.add("-classpath");
options.add(getClassPath());
我也看不出你把LoaderImpl
实例传递给compiler
的地方。不应该明确地做到吗?
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