min-velocity简化 velocity ​模板引擎

min-velocity 是一个专为代码生成而定制的简化 velocity 模板引擎。

目标：

以 velocity 1.7 为基础, 裁剪出适合用作代码生成的模板引擎

裁剪：

• 没有event机制

• 没有macro

• 没有stop

• 没有evaluate

• 没有define

• 没有break

改动：

• requires jdk1.5+

• 默认情况下，不打印任何日志

• 默认采用classpath模板加载器而非文件系统模板加载器

• default I/O encoding changed to UTF-8(from iso-8859-1)

• 对于#set指令，默认允许设置null值

• 默认打开resource cache

• 去掉了parser pool

• #parse和#include标签支持相对路径

• 新增$ParseUtil.recParsing("xxx.vm").addParam("key", val)模板调用形式；相当于带调用栈的#parse标签，能用在当你需要每层递归的context都相互隔离的递归#parse的时候；也能支持相对路径

• 可放置min-velocity.properties文件(可选)在classpath根路径下，用于覆盖velocity的各种默认属性

• min-velocity.properties可使用default.static.util.mappings属性配置默认的静态工具类，这 些工具类将被默认放入模板context中，可配置多个，如：default.static.util.mappings = ClassUtils:org.apache.commons.lang.ClassUtils

• 设置'stream.reference.rendering'开关(true/false)，默认关闭; 开启后，遇到reference是stream或reader的时候, 将读取stream或reader中的内容做渲染而非简单地toString渲染; 其中读取stream或reader的buffer可通过'stream.reference.rendering.buffer.size'配置大小 (默认为1024个字符); 亦可通过'stream.reference.rendering.limit'选项设置能够从流中读取的最大字符数限制(默认为100000)

• 支持String模板渲染，即直接将模板内容以String形式传入api进行渲染而不是只能选择传入一个模板路径

• 新增index.out.of.bounds.exception.suppress选项，当设置为true时，模板中对数组或list进行的取值或设置操作将忽略index out of bounds异常

For English speakers, see below:

• No event mechanism

• No macro

• No '#stop'

• No '#evaluate'

• No '#define'

• No '#break'

• requires jdk1.5+

• By default no logs rather than log to velocity.log

• defaults to use classapth resource loader

• I/O encoding defaults to UTF-8

• #set directive defaults to allow null value

• resource cache on by default

• parser pool removed

• relative path support for #parse and #include directives

• $ParseUtil.recParsing("xxx.vm").addParam("key", val) template parsing util added. You can see it as a '#parse' directive with invocation stack frame,
  which could easily do recursive parsing with isolated context in each round of recursion. This also supports relative path.

• could place an optional 'min-velocity.properties' file in classpath root to configure velocity runtime.

• min-velocity could contain zero or more 'default.static.util.mappings' property configs to expose static utility classes in template contexts, for example: default.static.util.mappings = ClassUtils:org.apache.commons.lang.ClassUtils, with this config you can reference to org.apache.commons.lang.ClassUtils class with key 'ClassUtils' anywhere.

• stream/reader reference rendering supported. If you set 'stream.reference.rendering'(default false) to 'true', min-velocity will dump the contents of a stream/reader reference rather than just invoking 'toString' on them while rendering. And the stream/reader reading buffer size could be specified by configuration 'stream.reference.rendering.buffer.size', measured in number of characters(default 1024). And further more, the maximum number of characters read from a stream could be limited by configuration 'stream.reference.rendering.limit'(default 100000).

• String literal templates rendering supported. Just specify template contents in a in-memory-String value to render, other than always specify a template path.

• When 'index.out.of.bounds.exception.suppress' option is setting to be 'true'，any 'IndexOutOfBoundsException' will be ignored when accessing or setting elements of arrays and lists.

Maven Central Repo:

<dependency>
    <groupId>com.github.pfmiles</groupId>
    <artifactId>min-velocity</artifactId>
    <version>1.0</version>
</dependency>

代码样例参见单元测试：

package com.github.pfmiles.minvelocity;

import java.io.StringReader;
import java.io.StringWriter;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import junit.framework.TestCase;

import com.github.pfmiles.org.apache.velocity.Template;

public class TemplateUtilTest extends TestCase {

    public void testRenderStringTemp() {
        String templateString = "#foreach($i in $list)\n$i\n#end";
        Map<String, Object> ctxPojo = new HashMap<String, Object>();
        List<String> list = new ArrayList<String>();
        list.add("one");
        list.add("two");
        list.add("three");
        ctxPojo.put("list", list);
        StringWriter out = new StringWriter();
        TemplateUtil.renderString(templateString, ctxPojo, out);
        // System.out.println(out.toString());
        assertTrue("one\ntwo\nthree\n".equals(out.toString()));
    }

    public void testRenderTemplate() {
        Template temp = TemplateUtil.parseStringTemplate("#foreach($i in $list)\n$i\n#end");
        Map<String, Object> ctxPojo = new HashMap<String, Object>();
        List<String> list = new ArrayList<String>();
        list.add("one");
        list.add("two");
        list.add("three");
        ctxPojo.put("list", list);
        StringWriter out = new StringWriter();
        TemplateUtil.renderTemplate(temp, ctxPojo, out);
        // System.out.println(out.toString());
        assertTrue("one\ntwo\nthree\n".equals(out.toString()));
    }

    public void testRefRendering() {
        Template temp = TemplateUtil.parseStringTemplate("hello $ref world");
        Map<String, Object> ctxPojo = new HashMap<String, Object>();
        StringReader stream = new StringReader("1234567890");
        ctxPojo.put("ref", stream);
        StringWriter writer = new StringWriter();
        TemplateUtil.renderTemplate(temp, ctxPojo, writer);
        assertTrue("hello 1234567890 world".equals(writer.toString()));
    }
}