目标是从远程位置加载一堆jar文件作为插件,在CDI上下文中初始化它们。
然后servlet可以像这样触发事件:
testEvent.fire(new EventTest("some message"));
该插件将能够观察到哪些内容。示例插件将如下所示:
public class Plugin{
public void respond (@Observes EventTest e){
//does something with the even object
}
}
这是应该加载插件的代码。从https://jaxenter.com/tips-for-writing-pluggable-java-ee-applications-105281.html获得并重新编写此类与servlet类位于同一个包中。它有必要的META-INF / services目录和javax.enterprise.inject.spi.Extension文件,该文件只有一行 - 扩展类的完全限定名:main.initplugins.InitPlugins。
package main.initplugins;
import java.sql.SQLException;
import java.sql.Connection;
import java.sql.Statement;
import java.util.jar.JarInputStream;
import java.util.jar.JarEntry;
import java.lang.ClassLoader;
import java.lang.reflect.Method;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.enterprise.event.Observes;
import javax.enterprise.inject.spi.BeforeBeanDiscovery;
import javax.enterprise.inject.spi.BeanManager;
public class InitPlugins implements javax.enterprise.inject.spi.Extension{
Logger log = Logger.getLogger("");
private java.util.Set<Class<?>> classes;
public void beforeBeanDiscovery(@Observes BeforeBeanDiscovery bbd, BeanManager bm){
log.log(Level.INFO, "LOAD PLUGINS HERE");
loadFromFiles();
try{
for (Class<?> cl: classes){
final javax.enterprise.inject.spi.AnnotatedType<?> at = bm.createAnnotatedType(cl);
bbd.addAnnotatedType(at);
log.log(Level.INFO, "ADD ANNOTATED TYPE FOR: " + cl.getName());
}
log.log(Level.INFO, "ANNOTATED TYPE CREATION COMPLETE");
} catch (Exception ex){
log.log(Level.INFO, "FAIL TO CREATE ANNOTATED TYPE: " + ex.getMessage());
}
}
public void loadFromFiles() {
classes = new java.util.LinkedHashSet<Class<?>>();
try{
//connect to a remote location. In this case it will be a database that holds the bytes of the .jar files
Connection dbConnection = java.sql.DriverManager.getConnection("jdbc:mysql://localhost/testdb?user=user&password=passwd");
Statement statement = dbConnection.createStatement();
java.sql.ResultSet plugins = statement.executeQuery("select * from plugins"); //the plugins table contain 2 columns: 1) fileName as primary key, 2) longblob that hold raw byte of the jar file
while (plugins.next()){
JarInputStream js = new JarInputStream(new java.io.ByteArrayInputStream(plugins.getBytes(2))); //load them as jar files, 2 is the index for the raw byte column that holds the jar file
JarEntry je;
while((je = js.getNextJarEntry()) != null){
//open each jar file, scan through file contents and find the .class files, then extract those bytes and pass them in the ClassLoader's defineClass method
if(!je.isDirectory() && je.getName().endsWith(".class")){
String className = je.getName().substring(0, je.getName().length() - 6).replace("/", ".");
log.log(Level.INFO, "class name is: " + className);
java.io.ByteArrayOutputStream classBytes = new java.io.ByteArrayOutputStream();
byte[] bytes;
try{
byte[] buffer = new byte[2048];
int read = 0;
while(js.available() > 0){
read = js.read(buffer, 0, buffer.length);
if(read > 0){
classBytes.write(buffer, 0, read);
}
}
bytes = classBytes.toByteArray();
//code below taken from: https://jaxenter.com/tips-for-writing-pluggable-java-ee-applications-105281.html
java.security.ProtectionDomain protDomain = getClass().getProtectionDomain();
ClassLoader cl = Thread.currentThread().getContextClassLoader();
Method tempDefineClassMethod = null;
for (Method tempMethod : ClassLoader.class.getDeclaredMethods()){
if(tempMethod.getName().equals("defineClass") && tempMethod.getParameterCount() == 5){
tempDefineClassMethod = tempMethod;
break;
}
}
final Method defineClassMethod = tempDefineClassMethod;
try{
java.security.AccessController.doPrivileged(new java.security.PrivilegedExceptionAction(){
@Override
public java.lang.Object run() throws Exception{
if (!defineClassMethod.isAccessible()){
defineClassMethod.setAccessible(true);
}
return null;
}
});
log.log(Level.INFO, "Attempting load class: " + className + " with lenght of: " + bytes.length);
defineClassMethod.invoke(cl, className, bytes, 0, bytes.length, protDomain);
classes.add(cl.loadClass(className));
log.log(Level.INFO, "Loaded class: " + je.getName());
} catch (Exception ex){
log.log(Level.INFO, "Error loading class: " + ex.getMessage());
ex.printStackTrace();
}
} catch (Exception ex){
log.log(Level.INFO, "Error loading bytes: " + ex.getMessage());
}
}
}
}
} catch (SQLException ex){
log.log(Level.SEVERE, "Fail to get db connection or create statement in plugin ejb: ".concat(ex.getMessage()));
} catch (Exception ex){
log.log(Level.SEVERE, "Fail to get db connection or create statement in plugin ejb: ".concat(ex.getMessage()));
}
}
}
由于某种原因,它不起作用。在任何阶段都不会抛出任何错误。当我从servlet中激活事件时,加载的插件无法获取它。我做错了什么?
答案 0 :(得分:2)
从CDI的角度来看,你的方法应该可以正常工作。
这里的问题是类加载,尤其是在考虑任何非平面部署时(除了纯SE之外)。
您选择使用TCCL,例如你做了:
ClassLoader cl = Thread.currentThread().getContextClassLoader();
在某些应用程序服务器/ servlet中,可能会为您提供与加载扩展本身(InitPlugin
)不同的类加载器。
相反,您应该使用加载扩展名的相同CL,因为它将是处理CDI bean的那个。所以,就这样做:
ClassLoader cl = InitPlugins.class.getClassLoader()
注意: 请注意,您正在航行未定义的水域。此行为/修复可能无法移植。