Documentation for Ice 3.5. Documentation for Ice 3.4 is also available.

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Inserting a User Exception in Java

As in the case of Ice objects, a Dynamic Ice application may represent user exceptions in a native format that is not directly compatible with the Ice API. If the application needs to raise such a user exception to the Ice run time, the exception must be wrapped in a subclass of Ice.UserException. The Dynamic Ice API provides a class to simplify this process:

package Ice;

public abstract class UserExceptionWriter extends UserException {

    public UserExceptionWriter(Communicator communicator);

    public abstract void write(Ice.OutputStream os);

    // ...

A subclass of UserExceptionWriter is responsible for supplying a communicator to the constructor, and for implementing the following methods:

Extracting a User Exception in Java

An application extracts a user exception by calling one of two versions of the throwException method defined in the InputStream class:

package Ice;
public interface InputStream {
    void throwException() throws UserException;
    void throwException(UserExceptionReaderFactory factory) throws UserException;

    // ...

The version without any arguments attempts to locate and throw a Java implementation of the encoded exception using classes generated by the Slice-to-Java compiler.

If your goal is to create an exception in another type system, such as a native PHP exception object, you must call the second version of throwException and pass an implementation of UserExceptionReaderFactory:

package Ice;

public interface UserExceptionReaderFactory {   
    void createAndThrow(String typeId) throws UserException;

As the stream iterates over slices of an exception from most-derived to least-derived, it invokes createAndThrow passing the type ID of each slice, giving the application an opportunity to raise an instance of UserExceptionReader:

package Ice;
public abstract class UserExceptionReader extends UserException {
    protected UserExceptionReader(Communicator communicator);

    public abstract void read(InputStream is);

    public abstract String ice_name();

    protected Communicator _communicator;

Subclasses of UserExceptionReader must implement the abstract functions. In particular, the implementation of read must call InputStream.startException, unmarshal the remaining slices, and then call InputStream.endException.

See Also

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