示例：SimpleSelectParser 解析 select 1+1; 输出 2；
0）总结
编写 JavaCC 模板，*.jj 文件。
编译生成代码文件。
移动代码文件到对应的包下。
调用生成的代码文件。
1）JavaCC 模板
main/javacc/SimpleSelectParser.jj
options {IGNORE_CASE = true;// 允许被多次初始化STATIC = false;
}PARSER_BEGIN(SimpleSelectParser)package cn.com.ptpress.cdm.parser.select;
import java.io.* ;public class SimpleSelectParser {private String sql;public void parse() throws ParseException {SelectExpr(sql);}public SimpleSelectParser(String expr) {this((Reader)(new StringReader(expr)));this.sql = expr;}public static void main(String[] args) throws Exception{final SimpleSelectParser parser = new SimpleSelectParser(String.join(" ", args));parser.parse();}
}PARSER_END(SimpleSelectParser)void SelectExpr(String sql) :
{int res;
}
{<SELECT>res = Expression(){System.out.println(sql + "=" + res);}
}int Expression() :
{int res = 0;int v;
}
{res = Number()(<ADD>v = Number(){res += v;}|<SUB>v = Number(){res -= v;})*{return res;}
}int Number() :
{Token t;
}
{t = <NUMBER>{return Integer.parseInt(t.image);}
}TOKEN :
{< SELECT: "SELECT" >
| < NUMBER: (["0"-"9"])+ >
| < ADD: "+" >
| < SUB: "-" >
}/*
跳过的制表符
* */
SKIP :
{" "
| "\t"
| "\n"
| "\r"
| "\f"
}
2）Java CC 的 Maven 插件
<build><plugins><plugin><groupId>org.codehaus.mojo</groupId><artifactId>javacc-maven-plugin</artifactId><version>2.6</version><executions><execution><phase>generate-sources</phase><id>javacc</id><goals><goal>javacc</goal></goals><configuration><sourceDirectory>${basedir}/src/main/javacc</sourceDirectory><includes><include>**/*.jj</include></includes><!-- <lookAhead>2</lookAhead>--><!-- <isStatic>false</isStatic>--><outputDirectory>${basedir}/generated-sources/</outputDirectory></configuration></execution></executions></plugin></plugins><resources><resource><directory>src/main/resources</directory></resource></resources></build>
3）执行编译命令
mvn org.codehaus.mojo:javacc-maven-plugin:2.6:javacc
生成的文件：
4）主类调用
1.将生成的文件移动到 .jj 文件配置的包下
2.启动 TestParser 类
package cn.com.ptpress.cdm.parser.select;public class TestParser {public static void main(String[] args) throws ParseException {parseSelect("select 1+1");parseSelect("select 1+1+1");parseSelect("select 1 + 3 - 5");}private static void parseSelect(String sql) throws ParseException {final SimpleSelectParser parser = new SimpleSelectParser(sql);// 解析的核心方法parser.parse();}
}
