JAVA分析器

用處：有時候爲了研究Javac的原理，要去看看class文件的內容是如何組織的，這時候很有必要查看class文件。根據編譯後生成的class文件，獲取JAVA信息，JAVA分析器代碼是個很好的選擇。

也可以使用javac編譯器把源文件編譯好，再接着使用javap工具查看class文件，命令如下 

javap -verbose HelloWorld

package tools;

import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.util.Scanner;

public class ClassAnalyzer {
    private static final String tab = "    ";//縮進

    /**
     * 調用該方法，並傳遞class文件名稱即可，比如ClassAnalyzer.analyzer("OutClassT1");//OutClassT1對應的是編譯後生成的class文件名稱
     * @param className
     * @throws ClassNotFoundException
     */
    public static void analyzer(String className) throws ClassNotFoundException {
        Class c = Class.forName(className);
        System.out.print(Modifier.toString(c.getModifiers()));
        System.out.print(" ");
        System.out.print(c.toString());
        Class superC = c.getSuperclass();
        if (superC != null) {
            System.out.print(" extends " + superC.getName());
        }
        System.out.println("{");//類開始括號
        //打印域
        System.out.println(tab + "//域");
        Field[] fields = c.getDeclaredFields();
        for (Field field : fields) {
            printField(field);
        }
        //打印構造器
        System.out.println(tab + "//構造器");
        Constructor[] constructors = c.getDeclaredConstructors();
        for (Constructor constructor : constructors) {
            printConstructor(constructor);
        }
        //打印方法
        System.out.println(tab + "//方法");
        Method[] methods = c.getDeclaredMethods();
        for (Method method : methods) {
            printMethod(method);
        }
        System.out.println("}");//類結束括號
    }

    //打印域
    private static void printField(Field field) {
        System.out.print(tab);
        System.out.print(Modifier.toString(field.getModifiers()));
        System.out.print(" ");
        Class fieldType = field.getType();
        if (fieldType.isArray()) {
            System.out.print(getArrayTypeName(fieldType));
        } else {
            System.out.print(field.getType().getName());
        }
        System.out.print(" ");
        System.out.print(field.getName());
        System.out.println(";");
    }

    //打印構造器
    private static void printConstructor(Constructor constructor) {
        System.out.print(tab);
        System.out.print(Modifier.toString(constructor.getModifiers()));
        System.out.print(" ");
        System.out.print(constructor.getDeclaringClass().getSimpleName());
        Class[] varTypes = constructor.getParameterTypes();
        System.out.print("(");
        printParameters(varTypes);
        System.out.println(");");
    }

    //打印方法
    private static void printMethod(Method method) {
        System.out.print(tab);
        System.out.print(Modifier.toString(method.getModifiers()));
        System.out.print(" ");
        Class returnType = method.getReturnType();
        if (returnType.isArray()) {
            System.out.print(getArrayTypeName(returnType));
        } else {
            System.out.print(method.getReturnType().getName());
        }
        System.out.print(" ");
        System.out.print(method.getName());
        System.out.print("(");
        Class[] varTypes = method.getParameterTypes();
        printParameters(varTypes);
        System.out.print(")");
        //聲明拋出的異常
        Class[] exceptionType = method.getExceptionTypes();
        if (exceptionType.length != 0) {
            System.out.print(" throws ");
            for (int i = 0; i < exceptionType.length; i++) {
                System.out.print(exceptionType[i].getName());
                if (i < (exceptionType.length - 1)) {
                    System.out.print(",");
                }
            }
        }
        System.out.println(";");
    }

    //打印構造器和方法的參數列表
    private static void printParameters(Class[] varTypes) {
        if (varTypes.length > 0) {
            for (int i = 0; i < varTypes.length; i++) {
                if (varTypes[i].isArray()) {
                    System.out.print(getArrayTypeName(varTypes[i]));
                } else {
                    System.out.print(varTypes[i].getName());
                }
                if (i < (varTypes.length - 1)) {
                    System.out.print(", ");
                }
            }
        } else {
            System.out.print(" ");
        }
    }

    public static String getArrayTypeName(Class type) {
        StringBuffer buffer = new StringBuffer(getArrayType(type).getName());
        int dimension = countArrayDimension(type);
        for (int i = 1; i <= dimension; i++) {
            buffer.append("[]");
        }
        return buffer.toString();
    }

    public static int countArrayDimension(Class type) {
        int dimension = 0;
        if (type.isArray()) {
            Class tempType = type;
            while ((tempType = tempType.getComponentType()) != null) {
                dimension++;
            }
        }
        return dimension;
    }

    public static Class getArrayType(Class type) {
        Class arrayType = null;
        if (type.isArray()) {
            Class tempType = type.getComponentType();
            do {
                arrayType = tempType;
            } while ((tempType = tempType.getComponentType()) != null);
        }
        return arrayType;
    }

    public static void main(String[] args) {
        try {
//            Scanner in = new Scanner(System.in);
//            System.out.print("Input class name:");
//            String className = in.next();
//            in.close();
            System.out.println("args = [" + 11111 + "]");
            String className = "com.wisely.learn.generic.DateInterval";
            analyzer(className);
        } catch (ClassNotFoundException ex) {
            ex.printStackTrace();
        }
    }
}