【ali SimpleEL】day1-优快云博客

本文链接：https://blog.youkuaiyun.com/iteye_5013/article/details/82327834

本文介绍了一种用于解析Java表达式的算法，并提供了一个具体的实现案例。该算法能够将带有注释的Java表达式转换为一系列Token，同时讨论了如何使用Java编译器将源代码编译为Class实例。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

将表达式（如 @a - @b + @c）中各部分解析为token并存放在List中，算法如下：

ExpressUtils.java

public static List<Token> parse(String expr) {

		List<Token> tokenList = new ArrayList<Token>();

		TokenType type = TokenType.Text;

		StringBuffer buf = new StringBuffer();
		char[] charArray = expr.toCharArray();
		for (int i = 0; i < charArray.length; ++i) {
			char ch = charArray[i];

			if (ch == '@') {
				if (buf.length() > 0) {
					tokenList.add(new Token(type, buf.toString()));
				}
				type = TokenType.Variant;
				buf = new StringBuffer();

				continue;
			}
			
			if (ch == '/' && i < charArray.length - 1 && charArray[i + 1] == '*') {
				if (buf.length() > 0) {
					tokenList.add(new Token(type, buf.toString()));
				}
				buf.append("/*");
				++i;
				type = TokenType.MultiLineComment;
				continue;
			}
			
			if (ch == '/' && i < charArray.length - 1 && charArray[i + 1] == '/') {
				if (buf.length() > 0) {
					tokenList.add(new Token(type, buf.toString()));
				}
				buf.append("//");
				++i;
				type = TokenType.LineComment;
				continue;
			}

			if (type == TokenType.Variant) {
				if (Character.isLetter(ch) || Character.isDigit(ch)) {
					buf.append(ch);
				} else if (ch == '_') {
					buf.append(ch);
				} else {
					tokenList.add(new Token(type, buf.toString()));
					type = TokenType.Text;
					buf = new StringBuffer();
					--i;
				}
				continue;
			}
			
			if (type == TokenType.Text) {
				buf.append(ch);
				continue;
			}
			
			if (type == TokenType.MultiLineComment) {
				if (ch == '*' && i < charArray.length - 1 && charArray[i + 1] == '/') {
					buf.append("*/");
					++i;
					tokenList.add(new Token(type, buf.toString()));
					type = TokenType.Text;
					buf = new StringBuffer();
					continue;
				} else {
					buf.append(ch);
				}
			}
			
			if (type == TokenType.LineComment) {
				if (ch == '\n') {
					buf.append(ch);
					tokenList.add(new Token(type, buf.toString()));
					type = TokenType.Text;
					buf = new StringBuffer();
				} else if (ch == '\r') {
					buf.append(ch);
					if (i < charArray.length - 1 && charArray[i + 1] == '\n') {
						buf.append(charArray[i + 1]);
						++i;
					}
					
					tokenList.add(new Token(type, buf.toString()));
					type = TokenType.Text;
					buf = new StringBuffer();
				} else {
					buf.append(ch);
				}
				continue;
			}
		}
		
		if (buf.length() > 0) {
			tokenList.add(new Token(type, buf.toString()));
		}
		
		return tokenList;
	}

将java源文件编译成类的Class型实例：JdkCompiler.java/JdkCompileTask.java

public synchronized Class<? extends Expr> compile(JavaSource javaSource) {
		compileCount.incrementAndGet();
		long startTimeMillis = System.nanoTime();

		try {
			final DiagnosticCollector<JavaFileObject> errs = new DiagnosticCollector<JavaFileObject>();

			JdkCompileTask<Expr> compileTask = new JdkCompileTask<Expr>(classLoader, options);

			String fullName = javaSource.getPackageName() + "." + javaSource.getClassName();

			return (Class<? extends Expr>) compileTask.compile(fullName, javaSource.getSource(), errs);
		} catch (JdkCompileException ex) {
			DiagnosticCollector<JavaFileObject> diagnostics = ex.getDiagnostics();

			throw new CompileExprException("compile error, source : \n" + javaSource + ", " + diagnostics.getDiagnostics(), ex);
		} catch (Exception ex) {
			throw new CompileExprException("compile error, source : \n" + javaSource, ex);
		} finally {
			// 编译时间统计
			compileTimeNano.addAndGet(System.nanoTime() - startTimeMillis);
		}
	}

待研究：

javax.tools.JavaCompiler.JavaCompiler compiler = javax.tools.ToolProvider.getSystemJavaCompiler().