98-thymeleaf

早期开发，完成的都是静态html页面。随着时间发展，引入了jsp，当在后端服务查询到数据之后可以转发到jsp页面，可以轻松的使用jsp页面来实现数据的显示及交互，jsp有非常强大的功能
但是，使用SpringBoot，整个项目是以jar包而不是war包的方式运行，而且还嵌入了Tomcat容器。因此默认情况下是不支持jsp。如果直接以纯静态页面方式会给开发带来很大麻烦，SpringBoot推荐使用模板引擎
模板引擎有很多种（jsp、freemarker、thymeleaf）。模板引擎的作用：将动态数据填充到页面模板指定位置，生成页面

1. 介绍

<!-- thymeleaf模板 -->
<dependency>
    <groupId>org.thymeleaf</groupId>
    <artifactId>thymeleaf-spring5</artifactId>
</dependency>
<dependency>
    <groupId>org.thymeleaf.extras</groupId>
    <artifactId>thymeleaf-extras-java8time</artifactId>
</dependency>

SpringBoot中有专门的thymeleaf配置类：ThymeleafProperties

@ConfigurationProperties(prefix = "spring.thymeleaf")
public class ThymeleafProperties {

	private static final Charset DEFAULT_ENCODING = StandardCharsets.UTF_8;

	public static final String DEFAULT_PREFIX = "classpath:/templates/";

	public static final String DEFAULT_SUFFIX = ".html";

	/**
	 * Whether to check that the template exists before rendering it.
	 */
	private boolean checkTemplate = true;

	/**
	 * Whether to check that the templates location exists.
	 */
	private boolean checkTemplateLocation = true;

	/**
	 * Prefix that gets prepended to view names when building a URL.
	 */
	private String prefix = DEFAULT_PREFIX;

	/**
	 * Suffix that gets appended to view names when building a URL.
	 */
	private String suffix = DEFAULT_SUFFIX;

	/**
	 * Template mode to be applied to templates. See also Thymeleaf's TemplateMode enum.
	 */
	private String mode = "HTML";

	/**
	 * Template files encoding.
	 */
	private Charset encoding = DEFAULT_ENCODING;

	/**
	 * Whether to enable template caching.
	 */
	private boolean cache = true;

	/**
	 * Order of the template resolver in the chain. By default, the template resolver is
	 * first in the chain. Order start at 1 and should only be set if you have defined
	 * additional "TemplateResolver" beans.
	 */
	private Integer templateResolverOrder;

	/**
	 * Comma-separated list of view names (patterns allowed) that can be resolved.
	 */
	private String[] viewNames;

	/**
	 * Comma-separated list of view names (patterns allowed) that should be excluded from
	 * resolution.
	 */
	private String[] excludedViewNames;

	/**
	 * Enable the SpringEL compiler in SpringEL expressions.
	 */
	private boolean enableSpringElCompiler;

	/**
	 * Whether hidden form inputs acting as markers for checkboxes should be rendered
	 * before the checkbox element itself.
	 */
	private boolean renderHiddenMarkersBeforeCheckboxes = false;

	/**
	 * Whether to enable Thymeleaf view resolution for Web frameworks.
	 */
	private boolean enabled = true;

	private final Servlet servlet = new Servlet();

	private final Reactive reactive = new Reactive();

}

2. 使用模板

@RequestMapping("/thymeleaf1")
public String thymeleaf1(Model model) {
    model.addAttribute("msg", "hello, thymeleaf");
    return "01_html";
}

<!DOCTYPE html>
<html lang="en" xmlns:th="http://www.thymeleaf.org">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
显示消息为：<p th:text="${msg}"></p>
</body>
</html>

3. 表达式语法

Simple expressions:
	Variable Expressions: ${...}
	Selection Variable Expressions: *{...}
	Message Expressions: #{...}
	Link URL Expressions: @{...}
	Fragment Expressions: ~{...}
Literals
	Text literals: 'one text', 'Another one!',…
	Number literals: 0, 34, 3.0, 12.3,…
	Boolean literals: true, false
	Null literal: null
	Literal tokens: one, sometext, main,…
Text operations:
	String concatenation: +
	Literal substitutions: |The name is ${name}|
Arithmetic operations:
	Binary operators: +, -, *, /, %
	Minus sign (unary operator): -
	Boolean operations:
	Binary operators: and, or
	Boolean negation (unary operator): !, not
Comparisons and equality:
	Comparators: >, <, >=, <= (gt, lt, ge, le)
	Equality operators: ==, != (eq, ne)
	Conditional operators:
	If-then: (if) ? (then)
	If-then-else: (if) ? (then) : (else)
	Default: (value) ?: (defaultvalue)
Special tokens:
	No-Operation: _

4. 实例演示

1. th常用属性值

th:text：设置当前元素的文本内容，相同功能的还有th:utext。前者不会转义html标签，后者会。优先级不高：order=7
th:value：设置当前元素的value值，类似修改指定属性的还有th:src，th:href。优先级不高：order=6
th:each：遍历循环元素，和th:text或th:value一起使用。注意该属性修饰的标签位置，详细往后看。优先级很高：order=2
th:if：条件判断，类似的还有th:unless，th:switch，th:case。优先级较高：order=3
th:insert：代码块引入，还有th:replace，th:include，三者区别较大，若使用不恰当会破坏html结构，常用于公共代码块提取。优先级最高：order=1
th:fragment：定义代码块，方便被th:insert引用。优先级最低：order=8
th:object：声明变量，一般和*{}一起配合使用，达到偷懒的效果。优先级一般：order=4
th:attr：修改任意属性，实际开发中用的较少，类似还有th:attrappend，th:attrprepend。优先级一般：order=5

<!DOCTYPE html>
<html lang="en" xmlns:th="http://www.thymeleaf.org">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<p th:text="${thText}"></p>
<p th:utext="${thUText}"></p>
<input type="text" th:value="${thValue}">
<div th:each="message:${thEach}">
    <p th:text="${message}"></p>
</div>
<div>
    <p th:text="${message}" th:each="message:${thEach}"></p>
</div>
<p th:text="${thIf}" th:if="${not #strings.isEmpty(thIf)}"></p>
<div th:object="${thObject}">
    <p>name:<span th:text="*{lastName}"/></p>
    <p>age:<span th:text="*{age}"/></p>
    <p>gender:<span th:text="*{sex}"/></p>
</div>
<p th:text="${session.name}"></p>
</body>
</html>

@RequestMapping("/thymeleaf2")
public String thymeleaf(ModelMap map, HttpSession session) {
    session.setAttribute("name", "zhangsan");

    map.put("thText", "th:text设置文本内容 <b>加粗</b>");
    map.put("thUText", "th:utext 设置文本内容 <b>加粗</b>");
    map.put("thValue", "thValue 设置当前元素的value值");
    map.put("thEach", "Arrays.asList(\"th:each\", \"遍历列表\")");
    map.put("thIf", "msg is not null");
    map.put("thObject", new Person("zhangsan", 12, "男"));
    return "thymeleaf";
}

2. 标准表达式

${...} 变量表达式（Variable Expressions）
*{...} 选择变量表达式（Selection Variable Expressions）

可以获取对象的属性和方法
可以使用ctx, vars, locale, request, response, session, servletContext内置对象
可以使用dates, numbers, strings, objects, arrays, lists, sets, maps等内置方法

session.setAttribute("user","zhangsan");

th:text="${session.user}"

strings：字符串格式化方法（equals(), equalsIgnoreCase(), length(), trim(), toUpperCase(), toLowerCase(), indexOf(), substring(), replace(), startsWith(), endsWith(), contains(), containsIgnoreCase()）
numbers：数值格式化方法（formatDecimal()）
boolean：布尔方法（isTrue(), isFalse()）
arrays：数组方法（toArray(), length(), isEmpty(), contains(), containsAll()）
lists、sets：集合方法（toList(), size(), isEmpty(), contains(), containsAll(), sort()）
maps：对象方法（size(), isEmpty(), containsKey(), containsValue()）
dates：日期方法（format(), year(), month(), hour(), createNow()）

<!DOCTYPE html>
<html lang="en" xmlns:th="http://www.thymeleaf.org">
<head>
    <meta charset="UTF-8">
    <title>thymeleaf内置方法</title>
</head>
<body>
<h3>#strings </h3>
<div th:if="${not #strings.isEmpty(Str)}">
    <p>Old Str : <span th:text="${Str}"/></p>
    <p>toUpperCase : <span th:text="${#strings.toUpperCase(Str)}"/></p>
    <p>toLowerCase : <span th:text="${#strings.toLowerCase(Str)}"/></p>
    <p>equals : <span th:text="${#strings.equals(Str, 'blog')}"/></p>
    <p>equalsIgnoreCase : <span th:text="${#strings.equalsIgnoreCase(Str, 'blog')}"/></p>
    <p>indexOf : <span th:text="${#strings.indexOf(Str, 'r')}"/></p>
    <p>substring : <span th:text="${#strings.substring(Str, 2, 4)}"/></p>
    <p>replace : <span th:text="${#strings.replace(Str, 'it', 'IT')}"/></p>
    <p>startsWith : <span th:text="${#strings.startsWith(Str, 'it')}"/></p>
    <p>contains : <span th:text="${#strings.contains(Str, 'IT')}"/></p>
</div>
<h3>#numbers </h3>
<div>
    <p>formatDecimal 整数部分随意，小数点后保留两位，四舍五入: <span th:text="${#numbers.formatDecimal(Num, 0, 2)}"/></p>
    <p>formatDecimal 整数部分保留五位数，小数点后保留两位，四舍五入: <span
            th:text="${#numbers.formatDecimal(Num, 5, 2)}"/></p>
</div>

<h3>#bools </h3>
<div th:if="${#bools.isTrue(Bool)}">
    <p th:text="${Bool}"></p>
</div>

<h3>#arrays </h3>
<div th:if="${not #arrays.isEmpty(Array)}">
    <p>length : <span th:text="${#arrays.length(Array)}"/></p>
    <p>contains : <span th:text="${#arrays.contains(Array,2)}"/></p>
    <p>containsAll : <span th:text="${#arrays.containsAll(Array, Array)}"/></p>
</div>
<h3>#lists </h3>
<div th:if="${not #lists.isEmpty(List)}">
    <p>size : <span th:text="${#lists.size(List)}"/></p>
    <p>contains : <span th:text="${#lists.contains(List, 0)}"/></p>
    <p>sort : <span th:text="${#lists.sort(List)}"/></p>
</div>
<h3>#maps </h3>
<div th:if="${not #maps.isEmpty(hashMap)}">
    <p>size : <span th:text="${#maps.size(hashMap)}"/></p>
    <p>containsKey : <span th:text="${#maps.containsKey(hashMap, 'thName')}"/></p>
    <p>containsValue : <span th:text="${#maps.containsValue(hashMap, '#maps')}"/></p>
</div>
<h3>#dates </h3>
<div>
    <p>format : <span th:text="${#dates.format(Date)}"/></p>
    <p>custom format : <span th:text="${#dates.format(Date, 'yyyy-MM-dd HH:mm:ss')}"/></p>
    <p>day : <span th:text="${#dates.day(Date)}"/></p>
    <p>month : <span th:text="${#dates.month(Date)}"/></p>
    <p>monthName : <span th:text="${#dates.monthName(Date)}"/></p>
    <p>year : <span th:text="${#dates.year(Date)}"/></p>
    <p>dayOfWeekName : <span th:text="${#dates.dayOfWeekName(Date)}"/></p>
    <p>hour : <span th:text="${#dates.hour(Date)}"/></p>
    <p>minute : <span th:text="${#dates.minute(Date)}"/></p>
    <p>second : <span th:text="${#dates.second(Date)}"/></p>
    <p>createNow : <span th:text="${#dates.createNow()}"/></p>
</div>
</body>
</html>

@RequestMapping("standardExpression")
public String standardExpression(ModelMap map) {
    map.put("Str", "Blog");
    map.put("Bool", true);
    map.put("Array", new Integer[]{1, 2, 3, 4});
    map.put("List", Arrays.asList(1, 3, 2, 4, 0));
    Map<String, Object> hashMap = new HashMap();
    hashMap.put("thName", "${#...}");
    hashMap.put("desc", "变量表达式内置方法");
    map.put("Map", hashMap);
    map.put("Date", new Date());
    map.put("Num", 888.888D);
    return "standardExpression";
}

3. 链接表达式

@{...}：链接表达式（Link URL Expressions）

<!--
    - 不管是静态资源的引用，form表单的请求，凡是链接都可以用@{...}。可以动态获取项目路径，即便项目名变了，依然可以正常访问
    - 链接表达式结构
        无参：@{/xxx}
        有参：@{/xxx(k1=v1,k2=v2)} 对应url结构：xxx?k1=v1&k2=v2

    - 引入本地资源：@{/项目本地的资源路径}
    - 引入外部资源：@{/webjars/资源在jar包中的路径}
-->
<link th:href="@{/webjars/bootstrap/4.0.0/css/bootstrap.css}" rel="stylesheet">
<link th:href="@{/main/css/123.css}" rel="stylesheet">
<form class="form-login" th:action="@{/user/login}" th:method="post" >
<a class="btn btn-sm" th:href="@{/login.html(l='zh_CN')}">中文</a>
<a class="btn btn-sm" th:href="@{/login.html(l='en_US')}">English</a>

4. 消息表达式

#{...}：消息表达式（Message Expressions）

<!--
    消息表达式一般用于国际化的场景。结构：th:text="#{msg}"
-->

5. 代码块表达式

{...}：代码块表达式（Fragment Expressions）

@RequestMapping("/fragment")
public String fragment() {
    return "fragment";
}

<!--
    支持两种语法结构
        推荐：~{templatename::fragmentname}
        支持：~{templatename::#id}
    - templatename：模版名，Thymeleaf会根据模版名解析完整路：/resources/templates/templatename.html，要注意文件的路径
    - fragmentname：片段名，Thymeleaf通过th:fragment声明定义代码块，即：th:fragment="fragmentname"
    - id：HTML的id选择器，使用时要在前面加上#号，不支持class选择器

    代码块表达式需要配合th属性`th:insert, th:replace, th:include`一起使用
    - th:insert：将代码块片段整个插入到使用了th:insert的HTML标签中
    - th:replace：将代码块片段整个替换使用了th:replace的HTML标签中
    - th:include：将代码块片段包含的内容插入到使用了th:include的HTML标签中
-->
<!DOCTYPE html>
<html lang="en" xmlns:th="http://www.thymeleaf.org">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>

<!-- th:fragment：定义代码块标识 -->
<footer th:fragment="copy">
    2019 The Good Thymes Virtual Grocery
</footer>

<!-- 三种不同的引入方式 -->
<div th:insert="fragment::copy"></div>
<div th:replace="fragment::copy"></div>
<div th:include="fragment::copy"></div>

<!-- th:insert：在div中插入代码块，即多了一层div -->
<div>
    <footer>
        &copy; 2011 The Good Thymes Virtual Grocery
    </footer>
</div>

<!-- th:replace：将代码块代替当前div，其html结构和之前一致 -->
<footer>
    &copy; 2011 The Good Thymes Virtual Grocery
</footer>

<!-- th:include：将代码块footer的内容插入到div中，即少了一层footer -->
<div>
    &copy; 2011 The Good Thymes Virtual Grocery
</div>
</body>
</html>

5. 国际化配置

在很多应用场景下，需要实现页面的国际化，SpringBoot对国际化有很好的支持

idea中设置统一的编码格式。file -> settings -> Editors -> File Encoding，选择编码格式为utf-8
resources资源文件下创建一个i8n目录，创建login.properties文件，还有login_zh_CN.properties文件，idea会自动识别国际化操作
创建三个不同的文件，名称分别是：login.properties，login_en_US.properties，login_zh_CN.properties

1. properties

# login.properties
login.password=密码1
login.remmber=记住我1
login.sign=登录1
login.username=用户名1

# login_en_US.properties
login.password=Password
login.remmber=Remember Me
login.sign=Sign In
login.username=Username

# login_zh_CN.properties
login.password=密码~
login.remmber=记住我~
login.sign=登录~
login.username=用户名~

2. yml

# 配置国际化的资源路径
spring:
  messages:
    basename: i18n/login

3. html

1. 原始页面

login0.html

<!DOCTYPE html>
<html lang="en" xmlns:th="http://www.thymeleaf.org">
<head>
    <meta charset="UTF-8"/>
    <title>Title</title>
</head>
<body>
<form action="" method="post">
    <label>Username</label>
    <input type="text" name="username" placeholder="Username">
    <label>Password</label>
    <input type="password" name="password" placeholder="Password">
    <br> <br>
    <div>
        <label>
            <input type="checkbox" value="remember-me"/> Remember Me
        </label>
    </div>
    <br>
    <button type="submit">Sign in</button>
    <br> <br>
    <a>中文</a>
    <a>English</a>
</form>
</body>
</html>

2. 跟随浏览器切换语言

login1.html

<!DOCTYPE html>
<html lang="en" xmlns:th="http://www.thymeleaf.org">
<head>
    <meta charset="UTF-8"/>
    <title>Title</title>
</head>
<body>
<form action="" method="post">
    <label th:text="#{login.username}">Username</label>
    <input type="text" name="username" placeholder="Username" th:placeholder="#{login.username}">
    <label th:text="#{login.password}">Password</label>
    <input type="password" name="password" placeholder="Password" th:placeholder="#{login.password}">
    <br> <br>
    <div>
        <label>
            <input type="checkbox" value="remember-me"/> [[#{login.remember}]]
        </label>
    </div>
    <br>
    <button type="submit" th:text="#{login.sign}">Sign in</button>
    <br> <br>
    <a>中文</a>
    <a>English</a>
</form>
</body>
</html>

3. 超链接实现

类比WebMvcAutoConfiguration$WebMvcAutoConfigurationAdapter#localeResolver()

package com.listao.spring_boot.config;

@Configuration
class MyConfig implements WebMvcConfigurer {

    @Override
    public void addViewControllers(ViewControllerRegistry registry) {
        registry.addViewController("/ooxx").setViewName("01_html");
        registry.addViewController("/login.html").setViewName("login");
    }

    @Bean
    public LocaleResolver localeResolver(){
        return new NativeLocaleResolver();
    }

    protected static class NativeLocaleResolver implements LocaleResolver {

        @Override
        public Locale resolveLocale(HttpServletRequest request) {
            String language = request.getParameter("language");
            Locale locale = Locale.getDefault();
            if(!StringUtils.isEmpty(language)){
                String[] split = language.split("_");
                locale = new Locale(split[0],split[1]);
            }
            return locale;
        }

        @Override
        public void setLocale(HttpServletRequest request, HttpServletResponse response, Locale locale) {

        }
    }

}

login.html

<!DOCTYPE html>
<html lang="en" xmlns:th="http://www.thymeleaf.org">
<head>
    <meta charset="UTF-8"/>
    <title>Title</title>
</head>
<body>
<form action="" method="post">
    <label th:text="#{login.username}">Username</label>
    <input type="text"  name="username"  placeholder="Username" th:placeholder="#{login.username}">
    <label th:text="#{login.password}">Password</label>
    <input type="password" name="password" placeholder="Password" th:placeholder="#{login.password}">
    <br> <br>
    <div>
        <label>
            <input type="checkbox" value="remember-me"/> [[#{login.remmber}]]
        </label>
    </div>
    <br>
    <button  type="submit" th:text="#{login.sign}">Sign in</button>
    <br> <br>
    <a th:href="@{/login.html(language='zh_CN')}">中文</a>
    <a th:href="@{/login.html(language='en_US')}">English</a>
</form>
</body>
</html>

4. 源码解释

1. MsgSourceAutoConfiguration

@Configuration(proxyBeanMethods = false)
@ConditionalOnMissingBean(name = AbstractApplicationContext.MESSAGE_SOURCE_BEAN_NAME, search = SearchStrategy.CURRENT)
@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
@Conditional(ResourceBundleCondition.class)
@EnableConfigurationProperties
public class MessageSourceAutoConfiguration {

    // 配置文件可以直接放在类路径下叫：messages.properties，就可以进行国际化操作了
	@Bean
	@ConfigurationProperties(prefix = "spring.messages")
	public MessageSourceProperties messageSourceProperties() {
		return new MessageSourceProperties();
	}

	@Bean
	public MessageSource messageSource(MessageSourceProperties properties) {
		ResourceBundleMessageSource messageSource = new ResourceBundleMessageSource();
		if (StringUtils.hasText(properties.getBasename())) {
		    // 设置国际化文件的基础名（去掉语言国家代码的）
			messageSource.setBasenames(StringUtils
					.commaDelimitedListToStringArray(StringUtils.trimAllWhitespace(properties.getBasename())));
		}
		if (properties.getEncoding() != null) {
			messageSource.setDefaultEncoding(properties.getEncoding().name());
		}
		messageSource.setFallbackToSystemLocale(properties.isFallbackToSystemLocale());
		Duration cacheDuration = properties.getCacheDuration();
		if (cacheDuration != null) {
			messageSource.setCacheMillis(cacheDuration.toMillis());
		}
		messageSource.setAlwaysUseMessageFormat(properties.isAlwaysUseMessageFormat());
		messageSource.setUseCodeAsDefaultMessage(properties.isUseCodeAsDefaultMessage());
		return messageSource;
	}

}

2. WebMvcAutoConfiguration

@Configuration(proxyBeanMethods = false)
@ConditionalOnWebApplication(type = Type.SERVLET)
@ConditionalOnClass({ Servlet.class, DispatcherServlet.class, WebMvcConfigurer.class })
@ConditionalOnMissingBean(WebMvcConfigurationSupport.class)
@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE + 10)
@AutoConfigureAfter({ DispatcherServletAutoConfiguration.class, TaskExecutionAutoConfiguration.class,
		ValidationAutoConfiguration.class })
public class WebMvcAutoConfiguration {

	public static final String DEFAULT_PREFIX = "";

	public static final String DEFAULT_SUFFIX = "";

	private static final String[] SERVLET_LOCATIONS = { "/" };


	// Defined as a nested config to ensure WebMvcConfigurer is not read when not
	// on the classpath
	@Configuration(proxyBeanMethods = false)
	@Import(EnableWebMvcConfiguration.class)
	@EnableConfigurationProperties({ WebMvcProperties.class, ResourceProperties.class })
	@Order(0)
	public static class WebMvcAutoConfigurationAdapter implements WebMvcConfigurer {

		@Bean
		@ConditionalOnMissingBean
		@ConditionalOnProperty(prefix = "spring.mvc", name = "locale")
		public LocaleResolver localeResolver() {
			if (this.mvcProperties.getLocaleResolver() == WebMvcProperties.LocaleResolver.FIXED) {
				return new FixedLocaleResolver(this.mvcProperties.getLocale());
			}
			AcceptHeaderLocaleResolver localeResolver = new AcceptHeaderLocaleResolver();
			localeResolver.setDefaultLocale(this.mvcProperties.getLocale());
			return localeResolver;
		}

    }

}

3. AcceptHeaderLocaleResolver

public class AcceptHeaderLocaleResolver implements LocaleResolver {

	private final List<Locale> supportedLocales = new ArrayList<>(4);

	@Nullable
	private Locale defaultLocale;

	@Override
	public Locale resolveLocale(HttpServletRequest request) {
		Locale defaultLocale = getDefaultLocale();
		if (defaultLocale != null && request.getHeader("Accept-Language") == null) {
			return defaultLocale;
		}
		Locale requestLocale = request.getLocale();
		List<Locale> supportedLocales = getSupportedLocales();
		if (supportedLocales.isEmpty() || supportedLocales.contains(requestLocale)) {
			return requestLocale;
		}
		Locale supportedLocale = findSupportedLocale(request, supportedLocales);
		if (supportedLocale != null) {
			return supportedLocale;
		}
		return (defaultLocale != null ? defaultLocale : requestLocale);
	}

}