编译原理

词法解析

// JavaParserpublic JCTree.JCCompilationUnit parseCompilationUnit() {        Token firstToken = token;        JCModifiers mods = null;        boolean consumedToplevelDoc = false;        boolean seenImport = false;        boolean seenPackage = false;        ListBuffer<JCTree> defs = new ListBuffer<>();        if (token.kind == MONKEYS_AT)            mods = modifiersOpt(); // 解析修饰符        if (token.kind == PACKAGE) { // 解析包声明            int packagePos = token.pos;            List<JCAnnotation> annotations = List.nil();            seenPackage = true;            if (mods != null) {                checkNoMods(mods.flags);                annotations = mods.annotations;                mods = null;            }            nextToken();            JCExpression pid = qualident(false);            accept(SEMI);            JCPackageDecl pd = toP(F.at(packagePos).PackageDecl(annotations, pid));            attach(pd, firstToken.comment(CommentStyle.JAVADOC));            consumedToplevelDoc = true;            defs.append(pd);        }        boolean checkForImports = true;        boolean firstTypeDecl = true;        while (token.kind != EOF) {            if (token.pos <= endPosTable.errorEndPos) {                // error recovery                skip(checkForImports, false, false, false);                if (token.kind == EOF)                    break;            }            if (checkForImports && mods == null && token.kind == IMPORT) { // 解析import                seenImport = true;                defs.append(importDeclaration());            } else { // 解析类主体                Comment docComment = token.comment(CommentStyle.JAVADOC); // 类doc注释                if (firstTypeDecl && !seenImport && !seenPackage) {                    docComment = firstToken.comment(CommentStyle.JAVADOC);                    consumedToplevelDoc = true;                }                if (mods != null || token.kind != SEMI)                    mods = modifiersOpt(mods);                if (firstTypeDecl && token.kind == IDENTIFIER) {                    ModuleKind kind = ModuleKind.STRONG; // 模块解析                    if (token.name() == names.open) {                        kind = ModuleKind.OPEN;                        nextToken();                    }                    if (token.kind == IDENTIFIER && token.name() == names.module) {                        if (mods != null) {                            checkNoMods(mods.flags & ~Flags.DEPRECATED);                        }                        defs.append(moduleDecl(mods, kind, docComment));                        consumedToplevelDoc = true;                        break;                    } else if (kind != ModuleKind.STRONG) {                        reportSyntaxError(token.pos, Errors.ExpectedModule);                    }                }                JCTree def = typeDeclaration(mods, docComment);                if (def instanceof JCExpressionStatement)                    def = ((JCExpressionStatement)def).expr;                defs.append(def);                if (def instanceof JCClassDecl)                    checkForImports = false;                mods = null;                firstTypeDecl = false;            }        }        JCTree.JCCompilationUnit toplevel = F.at(firstToken.pos).TopLevel(defs.toList());        if (!consumedToplevelDoc)            attach(toplevel, firstToken.comment(CommentStyle.JAVADOC));        if (defs.isEmpty())            storeEnd(toplevel, S.prevToken().endPos);        if (keepDocComments)            toplevel.docComments = docComments;        if (keepLineMap)            toplevel.lineMap = S.getLineMap();        this.endPosTable.setParser(null); // remove reference to parser        toplevel.endPositions = this.endPosTable;        return toplevel;    }

JavaParser 根据 Java 语言规范来解析.java文件进行词法解析

每调用一次nextToken 就会构造一个Token 

sequenceDiagram    Scanner ->> Names: 传char[]字符数组给fromChars方法    Names ->> Name.Table: table.fromChars    Name.Table ->> Name.Table: 根据char[]构建Name对象数组，数组索引是char[]的hash值    Name.Table ->> Names: ""    Names ->> Scanner: ""    Scanner ->> Keywords: 传Name对象到Keywords的key方法 查找相应的 Token    Keywords ->> Scanner: 根据name.getIndex查找key数组对应的Token

语法分析

JCExpression t = toP(F.at(token.pos).Ident(ident()));
protected JCTree importDeclaration() {    int pos = token.pos;    nextToken();    boolean importStatic = false;    if (token.kind == STATIC) {        importStatic = true;        nextToken();    }    JCExpression pid = toP(F.at(token.pos).Ident(ident()));    do {        int pos1 = token.pos;        accept(DOT);        if (token.kind == STAR) {            pid = to(F.at(pos1).Select(pid, names.asterisk));            nextToken();            break;        } else {            pid = toP(F.at(pos1).Select(pid, ident()));        }    } while (token.kind == DOT);    accept(SEMI);    return toP(F.at(pos).Import(pid, importStatic));}
JCTree typeDeclaration(JCModifiers mods, Comment docComment) {    int pos = token.pos;    if (mods == null && token.kind == SEMI) {        nextToken();        return toP(F.at(pos).Skip());    } else {        return classOrRecordOrInterfaceOrEnumDeclaration(modifiersOpt(mods), docComment);    }}

最后会生成一颗完整的语法树

语义分析

打磨语法树

代码生成

编译器API

JavaCompiler

编译文件

JavaCompiler javaCompiler = ToolProvider.getSystemJavaCompiler();javaCompiler.run(null,null,null,"path");

编译字符串

private static Class<?> compile(String className, String javaCodes) throws URISyntaxException {    class JavaSourceFromString extends SimpleJavaFileObject {        private final String src;        public JavaSourceFromString(String className, String code) throws URISyntaxException {            super(URI.create("string:///" + className.replace('.', '/')                    + ".java"), JavaFileObject.Kind.SOURCE);            this.src = code;        }        public String getCode() {return src;}        @Override        public CharSequence getCharContent(boolean ignoreEncodingErrors) {            return src;        }    }    //将字符串包装为SimpleJavaFileObject对象    JavaSourceFromString srcObject = new JavaSourceFromString(className, javaCodes);    System.out.println(srcObject.getCode());    Iterable<? extends JavaFileObject> fileObjects = Arrays.asList(srcObject);    JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();    StandardJavaFileManager fileManager = compiler.getStandardFileManager(null, null, null);    DiagnosticCollector<JavaFileObject> diagnosticCollector = new DiagnosticCollector<JavaFileObject>();    //设置编译的输出目录，并包装在options中    String flag = "-d";    String outDir = "";    try {        File classPath = new File(Thread.currentThread().getContextClassLoader().getResource("").toURI());        outDir = classPath.getAbsolutePath() + File.separator;        System.out.println(outDir);    } catch (URISyntaxException e1) {        e1.printStackTrace();    }    Iterable<String> options = Arrays.asList(flag, outDir);    //JavaCompiler.getTask方法：以future的任务形式(多线程)，来执行编译任务    // 第一个参数：额外输出流，null表示默认使用system.err    // 第二个参数：文件管理器，null表示编译器标准文件管理器    // 第三个参数：诊断监听器，null表示使用编译器默认方法来报告诊断信息    // 第四个参数：编译器参数，null表示无参数    // 第五个参数：需要经过annotation处理的类名，null表示没有类需要annotation处理    // 第六个参数：待编译的类    JavaCompiler.CompilationTask task =            compiler.getTask(null, fileManager, diagnosticCollector, options, null, fileObjects);    //等待编译结束    boolean result = task.call();    if (result) {        try {            return Class.forName(className);        } catch (ClassNotFoundException e) {            e.printStackTrace();        }    }    else    {        //print the Diagnostic's information        for  (Diagnostic diagnostic : diagnosticCollector                .getDiagnostics())        {            System.out.println("Error on line: "                    + diagnostic.getLineNumber() + "; URI: "                    + diagnostic.getSource().toString());        }    }    return null;}
String sourceCode = """public class HelloWorld {    public static void main(String[] args) {        System.out.println("hello world");    }}""";Class<?> klass = compile("HelloWorld", sourceCode);Method method = klass.getDeclaredMethod("main", String[].class);method.invoke(null, new Object[]{new String[]{}}); // print hello world

应用