014_哈希表内建函数

最新推荐文章于 2024-10-20 19:00:51 发布

自由与束缚JavaJavaScript

最新推荐文章于 2024-10-20 19:00:51 发布

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分类专栏： FreeMarker学习

本文链接：https://blog.youkuaiyun.com/aihiao/article/details/117432415

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1. keys

1.1. 一个包含哈希表中查找到的键的序列。

2. values

2.1. 一个包含哈希表中子变量的序列。

3. sort_by

3.1. 返回由给定的哈希表子变量来升序排序的哈希表序列。(要降序排列使用该内建函数后还要使用reverse内建函数。)这个规则和sort内建函数是一样的, 除了序列中的子变量必须是哈希表类型, 而且你不得不给哈希变量的名称, 那会用来决定排序顺序。

3.2. 如果你用来排序的子变量的层次很深(也就是说, 它是子变量的子变量的子变量, 以此类推), 那么你可以使用序列来作为参数, 它指定了子变量的名字, 来向下引导所需的子变量。

4. 例子

4.1. 新建一个名为FMBuiltInsForHash的动态Web工程, 同时添加相关jar包。

4.2. 编写FMFactory.java

package com.fm.util;

import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import freemarker.template.Configuration;
import freemarker.template.TemplateExceptionHandler;

public class FMFactory {
	private final static FMFactory instance = new FMFactory();
	private FMFactory() {}
	public static FMFactory getInstance() {
		return instance;
	}
	
	private Map<String, Configuration> map = new ConcurrentHashMap<String, Configuration>();
	
	// 创建单个Configuration实例
	public synchronized Configuration getCfg(Object servletContext, String path) {
		if(null != map.get(path)) {
			return map.get(path);
		}
		Configuration cfg = new Configuration(Configuration.VERSION_2_3_22);
		cfg.setServletContextForTemplateLoading(servletContext, path);
		cfg.setDefaultEncoding("utf-8");
		cfg.setTemplateExceptionHandler(TemplateExceptionHandler.RETHROW_HANDLER);
		map.put(path, cfg);
		
		return cfg;
	}
	
}

4.3. 编写BuiltInsForHash.java

package com.fm.action;

import java.io.IOException;
import java.io.OutputStreamWriter;
import java.io.Writer;
import java.util.HashMap;
import java.util.Map;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import com.fm.util.FMFactory;
import freemarker.template.Configuration;
import freemarker.template.Template;
import freemarker.template.TemplateException;

public class BuiltInsForHash extends HttpServlet {
	private static final long serialVersionUID = 1L;

	@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		Configuration cfg = FMFactory.getInstance().getCfg(req.getServletContext(), "/WEB-INF/templates");
		Template template = cfg.getTemplate("builtinsforhash.html");
		
		Map<String, Object> root = new HashMap<String, Object>();
		Writer out = new OutputStreamWriter(resp.getOutputStream());
		try {
			template.process(root, out);
		} catch (TemplateException e) {
			e.printStackTrace();
		}
	}
	
	@Override
	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		doGet(req, resp);
	}
}

4.4. 修改web.xml

4.5. 在/WEB-INF/templates下编写builtinsforhash.html

<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8" />
		<title>哈希表内建函数</title>
	</head>
	<body>
		<h2>一个包含哈希表中查找到的键的序列</h2>
		<#assign hash = {"name":"mouse", "price":50}>
		<#assign keys = hash?keys>
		<#list keys as key>${key} = ${hash[key]};<br /></#list>
		<h2>一个包含哈希表中子变量的序列</h2>
		<#assign values = hash?values>
		<#list values as value>${value}<br /></#list>
		<h2>返回由给定的哈希表子变量来升序排序的哈希表序列</h2>
		<#assign ls = [
			{"name":"whale", "weight":2000},
			{"name":"Barbara", "weight":53},
		  	{"name":"zeppelin", "weight":-200},
		  	{"name":"aardvark", "weight":30},
		  	{"name":"beetroot", "weight":0.3}
		]>
		Order by name:<br />
		<#list ls?sort_by("name") as i>
		- ${i.name}: ${i.weight}<br />
		</#list><br />
		Order by weight:<br />
		<#list ls?sort_by("weight") as i>
		- ${i.name}: ${i.weight}<br />
		</#list><br />
		<#assign members = [
	    	{"name": {"first": "Joe", "last": "Smith"}, "age": 40},
	    	{"name": {"first": "Fred", "last": "Crooger"}, "age": 35},
	    	{"name": {"first": "Amanda", "last": "Fox"}, "age": 25}]>
		Sorted by name.last: <br />
		<#list members?sort_by(['name', 'last']) as m>
		- ${m.name.last}, ${m.name.first}: ${m.age} years old<br />
		</#list>
	</body>
</html>

4.6. 运行项目