/*
* Copyright (c) 2002-2012 Alibaba Group Holding Limited.
* All rights reserved.
*
* 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.alibaba.citrus.service.velocity.impl;
import static com.alibaba.citrus.service.velocity.VelocityConfiguration.*;
import static com.alibaba.citrus.service.velocity.impl.SpringResourceLoaderAdapter.*;
import static com.alibaba.citrus.util.Assert.*;
import static com.alibaba.citrus.util.ObjectUtil.*;
import static com.alibaba.citrus.util.StringUtil.*;
import static org.apache.velocity.runtime.RuntimeConstants.*;
import java.io.IOException;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.StringWriter;
import java.io.UnsupportedEncodingException;
import java.io.Writer;
import com.alibaba.citrus.service.AbstractService;
import com.alibaba.citrus.service.configuration.ProductionModeAware;
import com.alibaba.citrus.service.template.TemplateContext;
import com.alibaba.citrus.service.template.TemplateException;
import com.alibaba.citrus.service.template.TemplateNotFoundException;
import com.alibaba.citrus.service.velocity.VelocityEngine;
import org.apache.velocity.Template;
import org.apache.velocity.app.event.EventCartridge;
import org.apache.velocity.app.event.ReferenceInsertionEventHandler;
import org.apache.velocity.context.AbstractContext;
import org.apache.velocity.context.Context;
import org.apache.velocity.context.InternalEventContext;
import org.apache.velocity.exception.MethodInvocationException;
import org.apache.velocity.exception.ParseErrorException;
import org.apache.velocity.exception.ResourceNotFoundException;
import org.apache.velocity.runtime.RuntimeServices;
import org.apache.velocity.util.RuntimeServicesAware;
import org.springframework.context.ResourceLoaderAware;
import org.springframework.core.io.ResourceLoader;
/**
* Velocity模板引擎服务。
*
* @author Michael Zhou
*/
public class VelocityEngineImpl extends AbstractService<VelocityEngine> implements VelocityEngine, ResourceLoaderAware,
ProductionModeAware {
private final static String RUNTIME_SERVICES_KEY = "_runtime_services";
private final VelocityRuntimeInstance ri = new VelocityRuntimeInstance();
private final VelocityConfigurationImpl configuration = new VelocityConfigurationImpl(getLogger());
public RuntimeServices getRuntimeServices() {
return ri;
}
public VelocityConfigurationImpl getConfiguration() {
return configuration;
}
public void setResourceLoader(ResourceLoader loader) {
configuration.setResourceLoader(loader);
}
public void setProductionMode(boolean productionMode) {
configuration.setProductionMode(productionMode);
}
/** 初始化engine。 */
@Override
protected void init() throws Exception {
configuration.init();
getLogger().debug("Velocity Engine Configurations: {}", configuration);
ri.setConfiguration(configuration.getProperties());
ri.setApplicationAttribute(SPRING_RESOURCE_LOADER_KEY, configuration.getResourceLoader());
ri.setProperty(EVENTHANDLER_REFERENCEINSERTION, RuntimeServicesExposer.class.getName());
ri.init();
// 初始化EventCartridge，以后不用再初始化了，以确保性能。
CloneableEventCartridge eventCartridge = configuration.getEventCartridge();
RuntimeServices rs = assertNotNull((RuntimeServices) ri.getProperty(RUNTIME_SERVICES_KEY), "RuntimeServices");
eventCartridge.initOnce(rs);
}
/**
* 取得默认的模板名后缀列表。
* <p>
* 当<code>TemplateService</code>没有指定到当前engine的mapping时，将取得本方法所返回的后缀名列表。
* </p>
*/
public String[] getDefaultExtensions() {
return new String[] { "vm" };
}
/** 判定模板是否存在。 */
public boolean exists(String templateName) {
return ri.getLoaderNameForResource(templateName) != null;
}
/** 渲染模板，并以字符串的形式取得渲染的结果。 */
public String getText(String templateName, TemplateContext context) throws TemplateException, IOException {
return mergeTemplate(templateName, new TemplateContextAdapter(context), null);
}
/** 渲染模板，并将渲染的结果送到字节输出流中。 */
public void writeTo(String templateName, TemplateContext context, OutputStream ostream) throws TemplateException,
IOException {
mergeTemplate(templateName, new TemplateContextAdapter(context), ostream, null, null);
}
/** 渲染模板，并将渲染的结果送到字符输出流中。 */
public void writeTo(String templateName, TemplateContext context, Writer writer) throws TemplateException,
IOException {
mergeTemplate(templateName, new TemplateContextAdapter(context), writer, null);
}
/** 渲染模板，并以字符串的形式取得渲染的结果。 */
public String mergeTemplate(String templateName, Context context, String inputEncoding) throws TemplateException,
IOException {
StringWriter writer = new StringWriter();
mergeTemplate(templateName, context, writer, inputEncoding);
return writer.toString();
}
/** 渲染模板，并将渲染的结果送到字节输出流中。 */
public void mergeTemplate(String templateName, Context context, OutputStream ostream, String inputEncoding,
String outputEncoding) throws TemplateException, IOException {
if (isEmpty(outputEncoding)) {
outputEncoding = getDefaultOutputEncoding();
}
OutputStreamWriter writer = null;
try {
writer = new OutputStreamWriter(ostream, outputEncoding);
} catch (UnsupportedEncodingException e) {
error(templateName, e);
}
mergeTemplate(templateName, context, writer, inputEncoding);
writer.flush(); // 确保内容被刷新到stream中。
}
/** 渲染模板，并将渲染的结果送到字符输出流中。 */
public void mergeTemplate(String templateName, Context context, Writer writer, String inputEncoding)
throws TemplateException, IOException {
if (isEmpty(inputEncoding)) {
inputEncoding = getDefaultInputEncoding();
}
try {
Context eventContext = attachEventCartridge(context);
mergeTemplate(templateName, inputEncoding, eventContext, writer);
} catch (Exception e) {
error(templateName, e);
}
}
/** Copied from org.apache.velocity.app.VelocityEngine。 */
private boolean mergeTemplate(String templateName, String encoding, Context context, Writer writer)
throws ResourceNotFoundException, ParseErrorException, MethodInvocationException, Exception {
Template template = ri.getTemplate(templateName, encoding);
if (template == null) {
String msg = "VelocityEngine.mergeTemplate() was unable to load template '" + templateName + "'";
ri.getLog().error(msg);
throw new ResourceNotFoundException(msg);
} else {
template.merge(context, writer);
return true;
}
}
private Context attachEventCartridge(Context context) {
Context eventContext;
if (context instanceof InternalEventContext) {
eventContext = context;
} else {
// 将其包装成EventContext，确保event cartridge可以工作。
// 模板中的修改将保留在context中。
eventContext = new EventContext(context);
}
// 将event cartridge复制以后（如有必要）附到context中。
EventCartridge ec = configuration.getEventCartridge().getRuntimeInstance();
if (ec != null) {
assertTrue(ec.attachToContext(eventContext), "Could not attach EventCartridge to velocity context");
}
return eventContext;
}
// 以下两个为性能优化
private String defaultInputEncoding;
private String defaultOutpuEncoding;
/** 取得解析模板时的默认编码字符集。 */
protected String getDefaultInputEncoding() {
if (defaultInputEncoding == null) {
defaultInputEncoding = defaultIfNull(trimToNull((String) ri.getProperty(INPUT_ENCODING)), DEFAULT_CHARSET);
}
return defaultInputEncoding;
}
/** 取得输出模板时的默认编码字符集。 */
protected String getDefaultOutputEncoding() {
if (defaultOutpuEncoding == null) {
defaultOutpuEncoding = defaultIfNull(trimToNull((String) ri.getProperty(OUTPUT_ENCODING)), DEFAULT_CHARSET);
}
return defaultOutpuEncoding;
}
/** 处理异常，显示额外的信息。 */
private final void error(String templateName, Throwable e) throws TemplateException {
String err = "Error rendering Velocity template: " + templateName;
getLogger().error(err + ": " + e.getMessage());
if (e instanceof ResourceNotFoundException) {
throw new TemplateNotFoundException(err, e);
}
if (e instanceof TemplateException) {
throw (TemplateException) e;
}
throw new TemplateException(err, e);
}
/** 一个hack，用来取得runtime services实例。 */
public static class RuntimeServicesExposer implements ReferenceInsertionEventHandler, RuntimeServicesAware {
public Object referenceInsert(String reference, Object value) {
return value;
}
public void setRuntimeServices(RuntimeServices rs) {
rs.getConfiguration().setProperty(RUNTIME_SERVICES_KEY, rs);
}
}
/** 包装任意<code>Context</code>，使之支持EventCartridge。 */
private static class EventContext extends AbstractContext {
private final Context context;
public EventContext(Context context) {
this.context = assertNotNull(context, "no context");
}
@Override
public Object internalGet(String key) {
return context.get(key);
}
@Override
public Object internalPut(String key, Object value) {
return context.put(key, value);
}
@Override
public boolean internalContainsKey(Object key) {
return context.containsKey(key);
}
@Override
public Object[] internalGetKeys() {
return context.getKeys();
}
@Override
public Object internalRemove(Object key) {
return context.remove(key);
}
@Override
public String toString() {
return context.toString();
}
}
}