Spring Boot 使用 Kotlin Script Template 模板引擎kts 开发web应用

2022-12-25 03:05| 来源: 网络整理| 查看: 265

在 Spring Framework 5.0 M4 中引入了一个专门的Kotlin支持。

Kotlin Script based templates ScriptTemplateView

从4.3版本开始，Spring Framework提供了一个 org.springframework.web.servlet.view.script.ScriptTemplateView 使用支持 JSR-223 的脚本引擎来渲染模板。

... /** * An {@link AbstractUrlBasedView} subclass designed to run any template library * based on a JSR-223 script engine. * *

If not set, each property is auto-detected by looking up a single * {@link ScriptTemplateConfig} bean in the web application context and using * it to obtain the configured properties. * *

Nashorn Javascript engine requires Java 8+, and may require setting the * {@code sharedEngine} property to {@code false} in order to run properly. See * {@link ScriptTemplateConfigurer#setSharedEngine(Boolean)} for more details. * * @author Sebastien Deleuze * @author Juergen Hoeller * @since 4.2 * @see ScriptTemplateConfigurer * @see ScriptTemplateViewResolver */ public class ScriptTemplateView extends AbstractUrlBasedView { public static final String DEFAULT_CONTENT_TYPE = "text/html"; private static final Charset DEFAULT_CHARSET = StandardCharsets.UTF_8; private static final String DEFAULT_RESOURCE_LOADER_PATH = "classpath:"; private static final ThreadLocal enginesHolder = new NamedThreadLocal("ScriptTemplateView engines"); private ScriptEngine engine; private String engineName; private Locale locale; private Boolean sharedEngine; private String[] scripts; private String renderObject; private String renderFunction; private Charset charset; private String[] resourceLoaderPaths; private ResourceLoader resourceLoader; private volatile ScriptEngineManager scriptEngineManager; ... }

这样我们就可以使用 kotlinx.html DSL或简单的Kotlin multiline String插值，编写kts类型安全模板。例如：

import com.easy.kotlin.kotlin_script_template.* """ ${include("header")}

Locale: FR | EN | 中文

${i18n("title")} ${include("users", mapOf(Pair("users", users)))} ${include("footer")} """ 新建一个SpringBoot + Kotlin 工程

首先，我们新建一个SpringBoot + Kotlin 工程，使用对应的版本分别是

kotlinVersion = '1.1.2' springBootVersion = '2.0.0.BUILD-SNAPSHOT'

使用gradle构建，配置如下：

buildscript { ext { kotlinVersion = '1.1.2' springBootVersion = '2.0.0.BUILD-SNAPSHOT' } repositories { mavenCentral() maven { url "http://dl.bintray.com/kotlin/kotlin-eap-1.1" } maven { url "https://repo.spring.io/snapshot" } maven { url "https://repo.spring.io/milestone" } } dependencies { classpath("org.springframework.boot:spring-boot-gradle-plugin:${springBootVersion}") classpath("org.jetbrains.kotlin:kotlin-gradle-plugin:${kotlinVersion}") classpath("org.jetbrains.kotlin:kotlin-allopen:${kotlinVersion}") } } apply plugin: 'kotlin' apply plugin: 'kotlin-spring' apply plugin: 'org.springframework.boot' jar { baseName = 'kotlin-script-templating' version = '0.0.1-SNAPSHOT' } repositories { mavenCentral() maven { url "http://dl.bintray.com/kotlin/kotlin-eap-1.1" } maven { url "https://repo.spring.io/snapshot" } maven { url "https://repo.spring.io/milestone" } } dependencies { compile("org.springframework.boot:spring-boot-starter-web:${springBootVersion}") compile("org.jetbrains.kotlin:kotlin-stdlib:${kotlinVersion}") compile("org.jetbrains.kotlin:kotlin-compiler:${kotlinVersion}") compile("org.jetbrains.kotlin:kotlin-script-util:${kotlinVersion}") { exclude group: "com.jcabi", module: "jcabi-aether" exclude group: "org.apache.maven", module: "maven-core" exclude group: "org.sonatype.aether", module: "aether-api" } testCompile("org.springframework.boot:spring-boot-starter-test:${springBootVersion}") } 工程目录结构

工程目录结构如下：

. ├── README.md ├── build │ └── kotlin-build │ └── caches │ └── version.txt ├── build.gradle ├── gradle │ └── wrapper │ ├── gradle-wrapper.jar │ └── gradle-wrapper.properties ├── gradlew ├── gradlew.bat └── src ├── main │ ├── java │ ├── kotlin │ │ └── com │ │ └── easy │ │ └── kotlin │ │ └── kotlin_script_template │ │ ├── Application.kt │ │ ├── Helpers.kt │ │ ├── User.kt │ │ └── ViewController.kt │ └── resources │ ├── META-INF │ │ └── services │ │ └── javax.script.ScriptEngineFactory │ ├── application.properties │ ├── banner.txt │ ├── messages.properties │ ├── messages_en.properties │ ├── messages_fr.properties │ ├── messages_zh.properties │ ├── scripts │ │ └── render.kts │ └── templates │ ├── footer.kts │ ├── header.kts │ ├── index.kts │ ├── user.kts │ └── users.kts └── test ├── java ├── kotlin │ └── com │ └── easy │ └── kotlin │ └── kotlin_script_template │ └── ApplicationTests.kt └── resources 26 directories, 25 files 配置脚本解析引擎的实现类

在META-INF/services/javax.script.ScriptEngineFactory文件里面加上其脚本解析引擎的实现类

org.jetbrains.kotlin.script.jsr223.KotlinJsr223JvmLocalScriptEngineFactory

其中，完成kts模板文件编译解析的类是KotlinJsr223JvmLocalScriptEngineFactory，这个类在kotlin-script-util包里。因为多了这一层编译解析，感觉速度慢了点。

配置Script Template Engine :

@SpringBootApplication class Application : WebMvcConfigurerAdapter() { /** * ScriptTemplateConfigurer * scripts/render.kts */ @Bean fun kotlinScriptConfigurer(): ScriptTemplateConfigurer { val configurer = ScriptTemplateConfigurer() configurer.engineName = "kotlin" configurer.setScripts("scripts/render.kts") configurer.renderFunction = "render" configurer.isSharedEngine = false return configurer } @Bean fun kotlinScriptViewResolver(): ViewResolver { val viewResolver = ScriptTemplateViewResolver() viewResolver.setPrefix("templates/") viewResolver.setSuffix(".kts") return viewResolver } @Bean fun localeResolver() = SessionLocaleResolver().apply { setDefaultLocale(Locale.CHINESE) } @Bean fun localeChangeInterceptor() = LocaleChangeInterceptor() override fun addInterceptors(registry: InterceptorRegistry) { registry.addInterceptor(localeChangeInterceptor()) } }

其中，LocaleChangeInterceptor() 是Spring框架里面定义的类

org.springframework.web.servlet.i18n.LocaleChangeInterceptor。

public class LocaleChangeInterceptor extends HandlerInterceptorAdapter { /** * Default name of the locale specification parameter: "locale". */ public static final String DEFAULT_PARAM_NAME = "locale"; protected final Log logger = LogFactory.getLog(getClass()); private String paramName = DEFAULT_PARAM_NAME; private String[] httpMethods; private boolean ignoreInvalidLocale = false; private boolean languageTagCompliant = false; ...

从上面的源码，我们可以看出它的默认query参数是locale。

渲染脚本render.kts

其中，render.kts代码如下：

import org.springframework.web.servlet.view.script.RenderingContext import org.springframework.context.support.ResourceBundleMessageSource import javax.script.* import org.springframework.beans.factory.getBean // TODO Use engine.eval(String, Bindings) when https://youtrack.jetbrains.com/issue/KT-15450 will be fixed fun render(template: String, model: Map, renderingContext: RenderingContext): String { val engine = ScriptEngineManager().getEngineByName("kotlin") val bindings = SimpleBindings(model) var messageSource = renderingContext.applicationContext.getBean() bindings.put("i18n", { code: String -> messageSource.getMessage(code, null, renderingContext.locale) }) bindings.put("include", { path: String -> renderingContext.templateLoader.apply("templates/$path.kts") }) engine.setBindings(bindings, ScriptContext.ENGINE_SCOPE) return engine.eval(template) as String } 模板绑定 ScriptTemplateWithBindings

我们上面在bindings里面添加了

bindings.put("i18n", { code: String -> messageSource.getMessage(code, null, renderingContext.locale) })

在index.kts这样调用

import com.easy.kotlin.kotlin_script_template.* """ ${include("header")}

Locale: FR | EN | 中文

${i18n("title")} ${include("users", mapOf(Pair("users", users)))} ${include("footer")} """

这个i18n在ScriptTemplateWithBindings类里的扩展函数如下

package com.easy.kotlin.kotlin_script_template import javax.script.ScriptContext import javax.script.ScriptEngineManager import javax.script.SimpleBindings import kotlin.script.templates.standard.ScriptTemplateWithBindings fun ScriptTemplateWithBindings.include(path: String, model: Map? = null) :String { val engine = ScriptEngineManager().getEngineByName("kotlin") var includeBindings = if (model != null) { val b = SimpleBindings(LinkedHashMap(model)) b["include"] = bindings["include"] b["i18n"] = bindings["i18n"] b } else { val b = SimpleBindings(bindings) b.remove("kotlin.script.history") b } engine.setBindings(includeBindings, ScriptContext.ENGINE_SCOPE) val template = (bindings["include"] as (String) -> String).invoke(path) return engine.eval(template) as String } fun ScriptTemplateWithBindings.i18n(code: String) = (bindings["i18n"] as (String) -> String).invoke(code) fun Iterable.joinToLine(function: (foo: T) -> String): String { return joinToString(separator = "\n") { foo -> function.invoke(foo) } } var ScriptTemplateWithBindings.users: List get() = bindings["users"] as List set(value) { throw UnsupportedOperationException()} var ScriptTemplateWithBindings.user: User get() = bindings["user"] as User set(value) { throw UnsupportedOperationException()} var ScriptTemplateWithBindings.title: String get() = bindings["title"] as String set(value) { throw UnsupportedOperationException()}

写实体类Usr，Controller类，最后写Spring Boot main函数:

fun main(args: Array) { SpringApplication.run(Application::class.java, *args) } 运行测试

命令行运行

gradle bootRun

启动运行，访问：http://localhost:8080/

你将看到如下输出页面

螢幕快照 2017-06-05 00.13.24.png 螢幕快照 2017-06-05 00.14.04.png 小结

本章节工程源代码：

https://github.com/EasyKotlin/kotlin-script-templating

使用Kotlin编写Spring Boot应用程序越多，我们越觉得这两种技术有着共同的目标，让我们广大程序员可以使用

富有表达性简短可读的代码

来更高效地编写应用程序，而Spring Framework 5 Kotlin支持将这些技术以更加自然，简单和强大的方式来展现给我们。

Kotlin可以用来编写基于注解的Spring Boot应用程序，但作为一种新的 functional and reactive applications 也将是一种很好的尝试，期待未来Spring Framework 5.0 和 Kotlin 结合的开发实践。

参考资料

https://github.com/sdeleuze/kotlin-script-templating

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