簡介
ANTLR是一款強大的語法分析器生成工具,可用於讀取,處理,執行和翻譯結構化的文本或二進制文件。它被廣泛用於工業實踐。大數據領域中熟知的hive,presto,spark都使用它來構建sql解析器。Twitter使用ANTLR進行語法分析,每天處理超過20億次查詢。
開發環境搭建
1.安裝idea antlr4插件
idea 提供了一個插件ANTLR v4 grammars plugin,可以非常方便的生成代碼。該插件可以在線安裝,也可以離線安裝,我選擇離線安裝。
下載地址:https://plugins.jetbrains.com/plugin/7358-antlr-v4-grammar-plugin/versions
版本:1.14
插件下載完成後,安裝即可。
2.生成代碼
創建Hello.g4,並新增如下內容,該程序用於匹配hello關鍵字。
// Define a grammar called Hello
grammar Hello;
r : 'hello' ID ; // match keyword hello followed by an identifier
ID : [a-z]+ ; // match lower-case identifiers
WS : [ \t\r\n]+ -> skip ; // skip spaces, tabs, newlines
配置ANTLR插件並生成響應的代碼
代碼實現
拷貝HelloBaseVisitor.java,HelloLexer.java,HelloListener.java,HelloParser.java,HelloVisitor.java到項目中
新增代碼
public class HelloVisitorImpl implements HelloVisitor {
public Object visitR(HelloParser.RContext ctx) {
return null;
}
public Object visit(ParseTree parseTree) {
return null;
}
public Object visitChildren(RuleNode ruleNode) {
return null;
}
public Object visitTerminal(TerminalNode terminalNode) {
return null;
}
public Object visitErrorNode(ErrorNode errorNode) {
return null;
}
}
HelloVisitorImpl.java
public class HelloMain {
public static void main(String[] args) {
CharStream input = CharStreams.fromString("hello\nhaha");
// 實例化詞法分析器
HelloLexer lexer=new HelloLexer(input);
CommonTokenStream tokens = new CommonTokenStream(lexer);
// 實例化解析器
HelloParser parser = new HelloParser(tokens);
ParseTree tree = parser.r();
HelloVisitorImpl myHelloVisitor = new HelloVisitorImpl();
myHelloVisitor.visit(tree);
System.out.println("result:"+ tree.toStringTree(parser));
}
}
HelloMain.java
<dependency>
<groupId>org.antlr</groupId>
<artifactId>antlr4-runtime</artifactId>
<version>4.8-1</version>
</dependency>
pom.xml中添加antlr4-runtime依賴
運行結果:
"C:\Program Files\Java\jdk1.8.0_192\bin\java.exe" "-javaagent:C:\Program Files\JetBrains\IntelliJ IDEA 2019.1.3\lib\idea_rt.jar=62242:C:\Program Files\JetBrains\IntelliJ IDEA 2019.1.3\bin" -Dfile.encoding=UTF-8 -classpath "C:\Program Files\Java\jdk1.8.0_192\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_192\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.8.0_192\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.8.0_192\jre\lib\ext\cldrdata.jar;C:\Program Files\Java\jdk1.8.0_192\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.8.0_192\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.8.0_192\jre\lib\ext\jfxrt.jar;C:\Program Files\Java\jdk1.8.0_192\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.8.0_192\jre\lib\ext\nashorn.jar;C:\Program Files\Java\jdk1.8.0_192\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.8.0_192\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.8.0_192\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.8.0_192\jre\lib\ext\sunpkcs11.jar;C:\Program Files\Java\jdk1.8.0_192\jre\lib\ext\zipfs.jar;C:\Program Files\Java\jdk1.8.0_192\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.8.0_192\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_192\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_192\jre\lib\jfxswt.jar;C:\Program Files\Java\jdk1.8.0_192\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_192\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.8.0_192\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.8.0_192\jre\lib\resources.jar;C:\Program Files\Java\jdk1.8.0_192\jre\lib\rt.jar;E:\antlr4\target\classes;E:\repository\org\antlr\antlr4-runtime\4.8-1\antlr4-runtime-4.8-1.jar" cn.aiaudit.hello.HelloMain
result:(r hello haha)
Process finished with exit code 0