MOQL—过滤器(Filter)

Filter是MOQL提供的主要功能之一，它支持SQL语法中Where部分的语法描述，能够通过编写条件语句对内存中的数据进行条件匹配。它可以用于对从数据库中查询回的数据集进行二次查询的功能；还能够用于数据处理时对数据流的实时过滤等。

Filter功能建立在Operand的基础上，Operand决定了能对哪些数据进行过滤。简单来说包括：常量、变量、数组、集合、对象等(详见文章MOQL—Operand(操作数))。这些数据必须封装在一个名为EntityMap的数据对象中，Filter就可以按照预定义的语法对数据进行匹配了。

Filter支持的运算符包括：关系运算符与逻辑运算符两大类。关系运算符包括：大于(>)、小于(<)、等于(=)、大于等于(>=)、小于等于(<=)、不等于(<>)、between..and、like、in、is等。逻辑运算符包括：逻辑与(and)、逻辑或(or)以及逻辑非(not)。关系运算符的运算优先级高于逻辑运算符，但所有关系运算符的优先级一致，没有差别。逻辑运算符的优先级中逻辑非(not)>逻辑与(and)>逻辑或 (or)。Filter也支持小括号”()”，可以通过小括号改变算符的执行顺序。

关系运算符的代码示例如下：

try {     EntityMap entityMap = new EntityMapImpl();     entityMap.putEntity("num", 123);     entityMap.putEntity("bean", new BeanA("bean", 100)     Filter filter = MoqlUtils.createFilter("num = 123");     System.out.println(filter.isMatch(entityMap));     filter = MoqlUtils.createFilter("num < 160");     System.out.println(filter.isMatch(entityMap));     filter = MoqlUtils.createFilter("bean.num > 0 ");     System.out.println(filter.isMatch(entityMap));     filter = MoqlUtils.createFilter("num <> 123");     System.out.println(filter.isMatch(entityMap));     filter = MoqlUtils.createFilter("num >= 123");     System.out.println(filter.isMatch(entityMap));     filter = MoqlUtils.createFilter("num <= 100");     System.out.println(filter.isMatch(entityMap));     // between..and     filter = MoqlUtils.createFilter("bean.num between 0 and 200");     System.out.println(filter.isMatch(entityMap));     filter = MoqlUtils.createFilter("bean.num between 0 and 100");     System.out.println(filter.isMatch(entityMap));     // like     filter = MoqlUtils.createFilter("bean.name like '%ean'");     System.out.println(filter.isMatch(entityMap));     filter = MoqlUtils.createFilter("bean.name like '%ea.'");     System.out.println(filter.isMatch(entityMap));     filter = MoqlUtils.createFilter("bean.name like '%e%'");     System.out.println(filter.isMatch(entityMap));     filter = MoqlUtils.createFilter("bean.name like '%c%'");     System.out.println(filter.isMatch(entityMap));     // in     filter = MoqlUtils.createFilter("bean.name in ('Abean', 'Bbean')");     System.out.println(filter.isMatch(entityMap));     filter = MoqlUtils.createFilter("bean.name in ('Cbean', 'Bbean')");     System.out.println(filter.isMatch(entityMap));     filter = MoqlUtils.createFilter("50 in (bean.getArray())");     System.out.println(filter.isMatch(entityMap));     filter = MoqlUtils.createFilter("150 in (bean.getArray())");     System.out.println(filter.isMatch(entityMap));     // is     filter = MoqlUtils.createFilter("bean.name is null");     System.out.println(filter.isMatch(entityMap));     filter = MoqlUtils.createFilter("bean.name is not null");     System.out.println(filter.isMatch(entityMap)); } catch (MoqlException e) {     e.printStackTrace(); }

逻辑运算符的代码示例如下：

try {     EntityMap entityMap = new EntityMapImpl();     entityMap.putEntity("num", 123);     entityMap.putEntity("bean", new BeanA("bean", 100));     Filter filter = MoqlUtils.createFilter("num > 100 and bean.num < 200 and bean.name like'%ean'");     System.out.println(filter.isMatch(entityMap));     filter = MoqlUtils.createFilter("bean.num > 0 and bean.num < 100");     System.out.println(filter.isMatch(entityMap));     // or     filter = MoqlUtils.createFilter("num > 150 or bean.num = 100");     System.out.println(filter.isMatch(entityMap));     filter = MoqlUtils.createFilter("num > 150 or bean.num <> 100");     System.out.println(filter.isMatch(entityMap));     // not     filter = MoqlUtils.createFilter("not bean.num <> 100");     System.out.println(filter.isMatch(entityMap));     filter = MoqlUtils.createFilter("not num > 150 or bean.num = 100");     //  paren     System.out.println(filter.isMatch(entityMap));     filter = MoqlUtils.createFilter("not (num > 150 or bean.num = 100)");     System.out.println(filter.isMatch(entityMap));     filter = MoqlUtils.createFilter("bean.num < 100 and num > 100 or bean.num = 100");     System.out.println(filter.isMatch(entityMap));     filter = MoqlUtils.createFilter("bean.num < 100 and (num > 100 or bean.num = 100)");     System.out.println(filter.isMatch(entityMap)); } catch (MoqlException e) {     e.printStackTrace(); }

以上两段代码的执行输出结果非常简单，在此不作赘述。示例中的Bean对象的定义可以通过下载MOQL的jar包获得，也可以随意自定义一个。MOQL的相关路径如下：

 

项目地址：http://sourceforge.net/projects/moql/

代码路径：svn://svn.code.sf.net/p/moql/code/trunk