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Diffstat (limited to 'src/main/java/com/google/escapevelocity/Template.java')
-rw-r--r-- | src/main/java/com/google/escapevelocity/Template.java | 112 |
1 files changed, 112 insertions, 0 deletions
diff --git a/src/main/java/com/google/escapevelocity/Template.java b/src/main/java/com/google/escapevelocity/Template.java new file mode 100644 index 0000000..646c42b --- /dev/null +++ b/src/main/java/com/google/escapevelocity/Template.java @@ -0,0 +1,112 @@ +/* + * Copyright (C) 2015 Google, Inc. + * + * Licensed 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 com.google.escapevelocity; + +import com.google.escapevelocity.EvaluationContext.PlainEvaluationContext; +import java.io.IOException; +import java.io.Reader; +import java.util.Map; + +/** + * A template expressed in EscapeVelocity, a subset of the Velocity Template Language (VTL) from + * Apache. The intent of this implementation is that if a template is accepted and successfully + * produces output, that output will be identical to what Velocity would have produced for the same + * template and input variables. + * + * @author emcmanus@google.com (Éamonn McManus) + */ +// TODO(emcmanus): spell out exactly what Velocity features are unsupported. +public class Template { + private final Node root; + + /** + * Used to resolve references to resources in the template, through {@code #parse} directives. + * + * <p>Here is an example that opens nested templates as resources relative to the calling class: + * + * <pre> + * ResourceOpener resourceOpener = resourceName -> { + * InputStream inputStream = getClass().getResource(resourceName); + * if (inputStream == null) { + * throw new IOException("Unknown resource: " + resourceName); + * } + * return new BufferedReader(InputStreamReader(inputStream, StandardCharsets.UTF_8)); + * }; + * </pre> + */ + @FunctionalInterface + public interface ResourceOpener { + + /** + * Returns a Reader that will be used to read the given resource, then closed. + * + * @param resourceName the name of the resource to be read. This will never be null. + */ + Reader openResource(String resourceName) throws IOException; + } + + /** + * Parses a VTL template from the given {@code Reader}. The given Reader will be closed on + * return from this method. + */ + public static Template parseFrom(final Reader reader) throws IOException { + ResourceOpener resourceOpener = new ResourceOpener() { + @Override + public Reader openResource(String resourceName) throws IOException { + if (resourceName == null) { + return reader; + } else { + throw new IOException("No ResourceOpener has been configured to read " + resourceName); + } + } + }; + try { + return parseFrom((String) null, resourceOpener); + } finally { + reader.close(); + } + } + + /** + * Parse a VTL template of the given name using the given {@code ResourceOpener}. + * + * @param resourceName name of the resource. May be null. + * @param resourceOpener used to open included files for {@code #parse} directives in the + * template. + */ + public static Template parseFrom( + String resourceName, ResourceOpener resourceOpener) throws IOException { + try (Reader reader = resourceOpener.openResource(resourceName)) { + return new Parser(reader, resourceName, resourceOpener).parse(); + } + } + + Template(Node root) { + this.root = root; + } + + /** + * Evaluate the given template with the given initial set of variables. + * + * @param vars a map where the keys are variable names and the values are the corresponding + * variable values. For example, if {@code "x"} maps to 23, then {@code $x} in the template + * will expand to 23. + * + * @return the string result of evaluating the template. + */ + public String evaluate(Map<String, ?> vars) { + EvaluationContext evaluationContext = new PlainEvaluationContext(vars); + return String.valueOf(root.evaluate(evaluationContext)); + } +} |