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FreeMarker is a "template engine"; a generic tool to generate text output based on templates.
/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
*/
package freemarker.template;
import java.io.IOException;
/**
* An interface that can be implemented by writers returned from
* {@link TemplateTransformModel#getWriter(java.io.Writer, java.util.Map)}. The
* methods on this
* interfaces are callbacks that will be called by the template engine and that
* give the writer a chance to better control the evaluation of the transform
* body. The writer can instruct the engine to skip or to repeat body
* evaluation, and gets notified about exceptions that are thrown during the
* body evaluation.
*/
public interface TransformControl {
/**
* Constant returned from {@link #afterBody()} that tells the
* template engine to repeat transform body evaluation and feed
* it again to the transform.
*/
public static final int REPEAT_EVALUATION = 0;
/**
* Constant returned from {@link #afterBody()} that tells the
* template engine to end the transform and close the writer.
*/
public static final int END_EVALUATION = 1;
/**
* Constant returned from {@link #onStart()} that tells the
* template engine to skip evaluation of the body.
*/
public static final int SKIP_BODY = 0;
/**
* Constant returned from {@link #onStart()} that tells the
* template engine to evaluate the body.
*/
public static final int EVALUATE_BODY = 1;
/**
* Called before the body is evaluated for the first time.
* @return
*
* - SKIP_BODY if the transform wants to ignore the body. In this
* case, only {@link java.io.Writer#close()} is called next and processing ends.
* - EVALUATE_BODY to normally evaluate the body of the transform
* and feed it to the writer
*
*/
public int onStart() throws TemplateModelException, IOException;
/**
* Called after the body has been evaluated.
* @return
*
* - END_EVALUATION if the transformation should be ended.
* - REPEAT_EVALUATION to have the engine re-evaluate the
* transform body and feed it again to the writer.
*
*/
public int afterBody() throws TemplateModelException, IOException;
/**
* Called if any exception occurs during the transform between the
* {@link TemplateTransformModel#getWriter(java.io.Writer, java.util.Map)} call
* and the {@link java.io.Writer#close()} call.
* @param t the throwable that represents the exception. It can be any
* non-checked throwable, as well as {@link TemplateException} and
* {@link java.io.IOException}.
*
* @throws Throwable is recommended that the methods rethrow the received
* throwable. If the method wants to throw another throwable, it should
* either throw a non-checked throwable, or an instance of
* {@link TemplateException} and {@link java.io.IOException}. Throwing any
* other checked exception will cause the engine to rethrow it as
* a {@link java.lang.reflect.UndeclaredThrowableException}.
*/
public void onError(Throwable t) throws Throwable;
}
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