我使用AST树使用Antlr 3开发了一个复杂的语法. ANTLR生成Lexer和Parser.问题是当用户输入例如无效的语法时,语法期望’;’.用户没有输入,然后在我的
Eclipse IDE中我得到以下异常：
line 1:24 mismatched input '<EOF>' expecting ';'
如何处理此异常,因为我试图捕获此异常,但是没有捕获异常.这是一个例外吗？我似乎不明白为什么没有抓到这个异常.我试图找出答案,但Antlr网站现在似乎已经停止了一段时间.
我查看了以下内容：ANTLR exception handling with “$”,Java并遵循该示例,但是当Lexer通过添加RuntimeException()生成代码时,我得到了无法访问的代码.
我不知道该怎么做.
编辑：
我找到了一个解决方案,通过查看：ANTLR not throwing errors on invalid input
但是,当我尝试获取Exception消息时,它为null.我是否正确设置了一切？请参阅示例语法：
grammar i;
options {
output=AST;
}
@header {
package com.data;
}
@rulecatch {
catch(RecognitionException e) {
throw e;
}
}
// by having these below it makes no difference
/**@parser::members {
@Override
public void reportError(RecognitionException e) {
throw new RuntimeException("Exception : " + " " + e.getMessage());
}
}
@lexer::members {
@Override
public void reportError(RecognitionException e) {
throw new RuntimeException("Exception : " + " " + e.getMessage());
}
}*/
编辑：
请看看我到目前为止：
grammar i;
options {
output=AST;
}
@header {
package com.data;
}
@rulecatch {
// ANTLR does not generate its normal rule try/catch
catch(RecognitionException e) {
throw e;
}
}
@parser::members {
@Override
public void displayRecognitionError(String[] tokenNames,RecognitionException e) {
String hdr = getErrorHeader(e);
String msg = getErrorMessage(e,tokenNames);
throw new RuntimeException(hdr + ":" + msg);
}
}
@lexer::members {
@Override
public void displayRecognitionError(String[] tokenNames,tokenNames);
throw new RuntimeException(hdr + ":" + msg);
}
}
operatorLogic : 'AND' | 'OR';
value : STRING;
query : (select)*;
select : 'SELECT'^ functions 'FROM table' filters?';';
operator : '=' | '!=' | '<' | '>' | '<=' | '>=';
filters : 'WHERE'^ conditions;
members : STRING operator value;
conditions : (members (operatorLogic members)*);
functions : '*';
STRING : ('a'..'z'|'A'..'Z')+;
WS : (' '|'\t'|'\f'|'\n'|'\r')+ {skip();}; // handle white space between keywords
public class Processor {
public Processor() {
}
/**
* This method builds the MQL Parser.
* @param args the args.
* @return the built IParser.
*/
private IParser buildMQLParser(String query) {
CharStream cs = new ANTLRStringStream(query);
// the input needs to be lexed
ILexer lexer = new ILexer(cs);
CommonTokenStream tokens = new CommonTokenStream();
IParser parser = new IParser(tokens);
tokens.setTokenSource(lexer);
// use the ASTTreeAdaptor so that the grammar is aware to build tree in AST format
parser.setTreeAdaptor((TreeAdaptor) new ASTTreeAdaptor().getASTTreeAdaptor());
return parser;
}
/**
* This method parses the MQL query.
* @param query the query.
*/
public void parseMQL(String query) {
IParser parser = buildMQLParser(query);
CommonTree commonTree = null;
try {
commonTree = (CommonTree) parser.query().getTree();
}
catch(Exception e) {
System.out.println("Exception :" + " " + e.getMessage());
}
}
}
public class ASTTreeAdaptor {
public ASTTreeAdaptor() {
}
/**
* This method is used to create a TreeAdaptor.
* @return a treeAdaptor.
*/
public Object getASTTreeAdaptor() {
TreeAdaptor treeAdaptor = new CommonTreeAdaptor() {
public Object create(Token payload) {
return new CommonTree(payload);
}
};
return treeAdaptor;
}
}
所以当我输入以下内容时：
SELECT * FROM表
没有 ‘;’我得到一个MismatchedTokenException：
catch(Exception e) {
System.out.println("Exception : " + " " e);
}
当我尝试：
e.getMessage();
它返回null.
解决方法
请尝试覆盖displayRecognitionError：
@parser::members {
...
@Override
public void displayRecognitionError(String[] tokenNames,tokenNames);
throw new RuntimeException(hdr + ":" + msg);
}
...
}
//same code in @lexer::members
如果要跟踪错误而不是中止,可以创建一个处理程序接口来跟踪它们：
@parser::members {
...
private YourErrorTrackerInterface errorTracker;
//getter/setter for errorTracker here
@Override
public void displayRecognitionError(String[] tokenNames,tokenNames);
if (errorTracker != null){
errorTracker.addError(e,tokenNames,hdr,msg);
}
}
...
}
//same code in @lexer::members
然后,错误跟踪器可以决定是抛出异常还是继续.
上面的代码允许您跟踪“可恢复”错误,ANTLR可以跳过的错误.仍然存在产生不可恢复错误的情况,例如SELECT * FROM table(没有结尾;).在这种情况下,您必须在parseMQL或其周围的某处捕获异常. (您可以尝试编写自己的恢复代码,但我不建议您这样做.)
这是一个修改过的parseMQL,它显示了两种不同类型的解析错误.请注意,我删除了对getMessage的调用,因为并非所有从RecognitionException派生的异常都会填充它.
public void parseMQL(String query) {
iParser parser = buildMQLParser(query);
CommonTree commonTree = null;
try {
commonTree = (CommonTree) parser.query().getTree();
} catch (MismatchedTokenException e){
//not production-quality code,just forming a useful message
String expected = e.expecting == -1 ? "<EOF>" : iParser.tokenNames[e.expecting];
String found = e.getUnexpectedType() == -1 ? "<EOF>" : iParser.tokenNames[e.getUnexpectedType()];
System.out.println("Fatal mismatched token exception: expected " + expected + " but was " + found);
} catch (RecognitionException e) {
System.out.println("Fatal recognition exception " + e.getClass().getName()
+ " : " + e);
} catch (Exception e) {
System.out.println("Other exception : " + e.getMessage());
}
}
输入SELECT * FROM表产生消息“致命不匹配令牌异常：预期’;’但是< EOF>“.此异常由ANTLR直接生成.
