com.facebook.buck.httpserver.TemplateHandler.java Source code

Introduction

Here is the source code for com.facebook.buck.httpserver.TemplateHandler.java

Source

/*
 * Copyright 2013-present Facebook, 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.facebook.buck.httpserver;

import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Preconditions;
import com.google.common.net.MediaType;
import com.google.template.soy.SoyFileSet;
import com.google.template.soy.data.SoyMapData;
import com.google.template.soy.tofu.SoyTofu;

import org.eclipse.jetty.server.Handler;
import org.eclipse.jetty.server.Request;
import org.eclipse.jetty.server.handler.AbstractHandler;

import java.io.IOException;
import java.net.URL;

import javax.annotation.Nullable;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * {@link Handler} that provides a response by populating a Soy template.
 */
class TemplateHandler extends AbstractHandler {

    /**
     * Whether to re-parse the templates for this handler on every request.
     * <p>
     * Should be set to {@code false} when checked in, but it is convenient to set this to
     * {@code true} in development.
     */
    private static final boolean DEBUG = Boolean.getBoolean("buck.soy.debug");

    private final TemplateHandlerDelegate delegate;

    /**
     * This field is set lazily by {@link #createAndMaybeCacheSoyTofu()}.
     */
    @Nullable
    private volatile SoyTofu tofu;

    /**
     * @param soyFiles The set of templates that can be used to produce a response from this handler.
     */
    protected TemplateHandler(TemplateHandlerDelegate templateBasedHandler) {
        this.delegate = Preconditions.checkNotNull(templateBasedHandler);
    }

    /**
     * Handles a request. Invokes {@link TemplateHandlerDelegate#getTemplateForRequest(Request)} to
     * get the template and {@link TemplateHandlerDelegate#getDataForRequest(Request)} to get the
     * template data, and then combines them to produce the response.
     */
    @Override
    public void handle(String target, Request baseRequest, HttpServletRequest request, HttpServletResponse response)
            throws IOException, ServletException {
        String html = createHtmlForResponse(baseRequest);
        if (html != null) {
            Responses.writeSuccessfulResponse(html, MediaType.HTML_UTF_8, baseRequest, response);
        } else {
            Responses.writeFailedResponse(baseRequest, response);
        }
    }

    @Nullable
    String createHtmlForResponse(Request baseRequest) throws IOException {
        String template = delegate.getTemplateForRequest(baseRequest);
        SoyTofu.Renderer renderer = createAndMaybeCacheSoyTofu().newRenderer(template);

        SoyMapData data = delegate.getDataForRequest(baseRequest);
        if (data != null) {
            renderer.setData(data);
            return renderer.render();
        } else {
            return null;
        }
    }

    @VisibleForTesting
    TemplateHandlerDelegate getDelegate() {
        return delegate;
    }

    /**
     * Returns the {@link SoyTofu} for the {@link #soyFiles}. If {@link #DEBUG} is {@code false}, then
     * the result will be cached because {@link SoyTofu} objects can be expensive to construct.
     */
    private SoyTofu createAndMaybeCacheSoyTofu() {
        // In debug mode, create a new SoyTofu object for each request. This makes it possible to test
        // new versions of the templates without restarting buckd.
        if (DEBUG) {
            return createSoyTofu();
        }

        // In production, cache the SoyTofu object for efficiency.
        if (tofu != null) {
            return tofu;
        }

        synchronized (this) {
            if (tofu == null) {
                tofu = createSoyTofu();
            }
        }
        return tofu;
    }

    /** Creates the {@link SoyTofu} for the {@link #soyFiles}. */
    private SoyTofu createSoyTofu() {
        SoyFileSet.Builder builder = new SoyFileSet.Builder();
        for (String soyFile : delegate.getTemplates()) {
            URL url = delegate.getClass().getResource(soyFile);
            builder.add(url);
        }
        return builder.build().compileToTofu();
    }
}