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/*
* 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.FilterWriter;
import java.io.IOException;
import java.io.Writer;
import java.util.Map;
import freemarker.template.utility.DeepUnwrap;
/**
* "transform" template language data type: user-defined directives
* (much like macros) specialized on filtering output; you should rather use the newer {@link TemplateDirectiveModel}
* instead. This interface will certainly be deprecated in FreeMarker 2.4.
*/
public interface TemplateTransformModel extends TemplateModel {
/**
* Returns a writer that will be used by the engine to feed the transformation input to the transform. Each call to
* this method must return a new instance of the writer so that the transformation is thread-safe.
*
* This method should not throw {@link RuntimeException}, nor {@link IOException} that wasn't caused by writing to
* the output. Such exceptions should be catched inside the method and wrapped inside a
* {@link TemplateModelException}. (Note that setting {@link Configuration#setWrapUncheckedExceptions(boolean)} to
* {@code true} can mitigate the negative effects of implementations that throw {@link RuntimeException}-s.)
*
* @param out
* the character stream to which to write the transformed output
*
* @param args
* the arguments (if any) passed to the transformation as a map of key/value pairs where the keys are
* strings and the arguments are {@link TemplateModel} instances. This is never {@code null}. (If you
* need to convert the template models to POJOs, you can use the utility methods in the
* {@link DeepUnwrap} class. Though it's recommended to work with {@link TemplateModel}-s directly.)
*
* @return The {@link Writer} to which the engine will write the content to transform, or {@code null} if the
* transform does not support nested content (body). The returned {@link Writer} may implements the
* {@link TransformControl} interface if it needs advanced control over the evaluation of the nested
* content. FreeMarker will call {@link Writer#close()} after the transform end-tag. {@link Writer#close()}
* must not close the {@link Writer} received as the {@code out} parameter (so if you are using a
* {@link FilterWriter}, you must override {@link FilterWriter#close()}, as by default that closes the
* wrapped {@link Writer}). Since 2.3.27 its also allowed to return the {@code out} writer as is, in which
* case it won't be closed.
*
* @throws TemplateModelException
* If any problem occurs that's not an {@link IOException} during writing the template output.
* @throws IOException
* When writing to {@code out} (the parameter) fails. Other {@link IOException}-s should be catched in
* this method and wrapped into {@link TemplateModelException}.
*/
Writer getWriter(Writer out, Map args) throws TemplateModelException, IOException;
}