javax.activation.CommandInfo Maven / Gradle / Ivy
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package javax.activation;
import java.io.*;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.security.AccessController;
import java.security.PrivilegedAction;
/**
* The CommandInfo class is used by CommandMap implementations to
* describe the results of command requests. It provides the requestor
* with both the verb requested, as well as an instance of the
* bean. There is also a method that will return the name of the
* class that implements the command but it is not guaranteed to
* return a valid value. The reason for this is to allow CommandMap
* implmentations that subclass CommandInfo to provide special
* behavior. For example a CommandMap could dynamically generate
* JavaBeans. In this case, it might not be possible to create an
* object with all the correct state information solely from the class
* name.
*/
public class CommandInfo {
private String verb;
private String className;
/**
* The Constructor for CommandInfo.
* @param verb The command verb this CommandInfo decribes.
* @param className The command's fully qualified class name.
*/
public CommandInfo(String verb, String className) {
this.verb = verb;
this.className = className;
}
/**
* Return the command verb.
*
* @return the command verb.
*/
public String getCommandName() {
return verb;
}
/**
* Return the command's class name. This method MAY return null in
* cases where a CommandMap subclassed CommandInfo for its
* own purposes. In other words, it might not be possible to
* create the correct state in the command by merely knowing
* its class name. DO NOT DEPEND ON THIS METHOD RETURNING
* A VALID VALUE!
*
* @return The class name of the command, or null
*/
public String getCommandClass() {
return className;
}
/**
* Return the instantiated JavaBean component.
*
* If the current runtime environment supports
* {@link java.beans.Beans#instantiate Beans.instantiate},
* use it to instantiate the JavaBeans component. Otherwise, use
* {@link java.lang.Class#forName Class.forName}.
*
* The component class needs to be public.
* On Java SE 9 and newer, if the component class is in a named module,
* it needs to be in an exported package.
*
* If the bean implements the javax.activation.CommandObject
* interface, call its setCommandContext method.
*
* If the DataHandler parameter is null, then the bean is
* instantiated with no data. NOTE: this may be useful
* if for some reason the DataHandler that is passed in
* throws IOExceptions when this method attempts to
* access its InputStream. It will allow the caller to
* retrieve a reference to the bean if it can be
* instantiated.
*
* If the bean does NOT implement the CommandObject interface,
* this method will check if it implements the
* java.io.Externalizable interface. If it does, the bean's
* readExternal method will be called if an InputStream
* can be acquired from the DataHandler.
*
* @param dh The DataHandler that describes the data to be
* passed to the command.
* @param loader The ClassLoader to be used to instantiate the bean.
* @return The bean
* @exception IOException for failures reading data
* @exception ClassNotFoundException if command object class can't
* be found
* @see java.beans.Beans#instantiate
* @see javax.activation.CommandObject
*/
public Object getCommandObject(DataHandler dh, ClassLoader loader)
throws IOException, ClassNotFoundException {
Object new_bean = null;
// try to instantiate the bean
new_bean = Beans.instantiate(loader, className);
// if we got one and it is a CommandObject
if (new_bean != null) {
if (new_bean instanceof CommandObject) {
((CommandObject)new_bean).setCommandContext(verb, dh);
} else if (new_bean instanceof Externalizable) {
if (dh != null) {
InputStream is = dh.getInputStream();
if (is != null) {
((Externalizable)new_bean).readExternal(
new ObjectInputStream(is));
}
}
}
}
return new_bean;
}
/**
* Helper class to invoke Beans.instantiate reflectively or the equivalent
* with core reflection when module java.desktop is not readable.
*/
private static final class Beans {
static final Method instantiateMethod;
static {
Method m;
try {
Class c = Class.forName("java.beans.Beans");
m = c.getDeclaredMethod("instantiate", ClassLoader.class, String.class);
} catch (ClassNotFoundException e) {
m = null;
} catch (NoSuchMethodException e) {
m = null;
}
instantiateMethod = m;
}
/**
* Equivalent to invoking java.beans.Beans.instantiate(loader, cn)
*/
static Object instantiate(ClassLoader loader, String cn)
throws IOException, ClassNotFoundException {
Exception exception;
if (instantiateMethod != null) {
// invoke Beans.instantiate
try {
return instantiateMethod.invoke(null, loader, cn);
} catch (InvocationTargetException e) {
exception = e;
} catch (IllegalAccessException e) {
exception = e;
}
} else {
SecurityManager security = System.getSecurityManager();
if (security != null) {
// if it's ok with the SecurityManager, it's ok with me.
String cname = cn.replace('/', '.');
if (cname.startsWith("[")) {
int b = cname.lastIndexOf('[') + 2;
if (b > 1 && b < cname.length()) {
cname = cname.substring(b);
}
}
int i = cname.lastIndexOf('.');
if (i != -1) {
security.checkPackageAccess(cname.substring(0, i));
}
}
// Beans.instantiate specified to use SCL when loader is null
if (loader == null) {
loader = (ClassLoader)
AccessController.doPrivileged(new PrivilegedAction() {
public Object run() {
ClassLoader cl = null;
try {
cl = ClassLoader.getSystemClassLoader();
} catch (SecurityException ex) { }
return cl;
}
});
}
Class beanClass = Class.forName(cn, true, loader);
try {
return beanClass.newInstance();
} catch (Exception ex) {
throw new ClassNotFoundException(beanClass + ": " + ex, ex);
}
}
return null;
}
}
}