Java基础20-从IDE的实现原理聊起，谈谈那些年我们用过的Java命令（一）

    public class MyIDE {复制代码

        public static void main(String[] args) throws IOException, ClassNotFoundException, NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException {
            // 定义java代码，并保存到文件（Test.java）
            StringBuilder sb = new StringBuilder();
            sb.append("package com.tommy.core.test.reflect;\n");
            sb.append("public class Test {\n");
            sb.append("    private String name;\n");
            sb.append("    public Test(String name){\n");
            sb.append("        this.name = name;\n");
            sb.append("        System.out.println(\"hello,my name is \" + name);\n");
            sb.append("    }\n");
            sb.append("    public String sayHello(String name) {\n");
            sb.append("        return \"hello,\" + name;\n");
            sb.append("    }\n");
            sb.append("}\n");复制代码

            System.out.println(sb.toString());复制代码

            String baseOutputDir = "F:\\output\\classes\\";
            String baseDir = baseOutputDir + "com\\tommy\\core\\test\\reflect\\";
            String targetJavaOutputPath = baseDir + "Test.java";
            // 保存为java文件
            FileWriter fileWriter = new FileWriter(targetJavaOutputPath);
            fileWriter.write(sb.toString());
            fileWriter.flush();
            fileWriter.close();复制代码

            // 编译为class文件
            JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
            StandardJavaFileManager manager = compiler.getStandardFileManager(null,null,null);
            List<File> files = new ArrayList<>();
            files.add(new File(targetJavaOutputPath));
            Iterable compilationUnits = manager.getJavaFileObjectsFromFiles(files);复制代码

            // 编译
            // 设置编译选项，配置class文件输出路径
            Iterable<String> options = Arrays.asList("-d",baseOutputDir);
            JavaCompiler.CompilationTask task = compiler.getTask(null, manager, null, options, null, compilationUnits);
            // 执行编译任务
            task.call();
    复制代码

            // 通过反射得到对象
    //        Class clazz = Class.forName("com.tommy.core.test.reflect.Test");
            // 使用自定义的类加载器加载class
            Class clazz = new MyClassLoader(baseOutputDir).loadClass("com.tommy.core.test.reflect.Test");
            // 得到构造器
            Constructor constructor = clazz.getConstructor(String.class);
            // 通过构造器new一个对象
            Object test = constructor.newInstance("jack.tsing");
            // 得到sayHello方法
            Method method = clazz.getMethod("sayHello", String.class);
            // 调用sayHello方法
            String result = (String) method.invoke(test, "jack.ma");
            System.out.println(result);
        }
    }复制代码

    
    public class MyClassLoader extends ClassLoader {
        private String baseDir;
        public MyClassLoader(String baseDir) {
            this.baseDir = baseDir;
        }
        @Override
        protected Class<?> findClass(String name) throws ClassNotFoundException {
            String fullClassFilePath = this.baseDir + name.replace("\\.","/") + ".class";
            File classFilePath = new File(fullClassFilePath);
            if (classFilePath.exists()) {
                FileInputStream fileInputStream = null;
                ByteArrayOutputStream byteArrayOutputStream = null;
                try {
                    fileInputStream = new FileInputStream(classFilePath);
                    byte[] data = new byte[1024];
                    int len = -1;
                    byteArrayOutputStream = new ByteArrayOutputStream();
                    while ((len = fileInputStream.read(data)) != -1) {
                        byteArrayOutputStream.write(data,0,len);
                    }复制代码

                    return defineClass(name,byteArrayOutputStream.toByteArray(),0,byteArrayOutputStream.size());
                } catch (FileNotFoundException e) {
                    e.printStackTrace();
                } catch (IOException e) {
                    e.printStackTrace();
                } finally {
                    if (null != fileInputStream) {
                        try {
                            fileInputStream.close();
                        } catch (IOException e) {
                            e.printStackTrace();
                        }
                    }复制代码

                    if (null != byteArrayOutputStream) {
                        try {
                            byteArrayOutputStream.close();
                        } catch (IOException e) {
                            e.printStackTrace();
                        }
                    }
                }
            }
            return super.findClass(name);
        }
    }    复制代码

    <?xml version="1.0" encoding="UTF-8"?>
    <classpath>
    <classpathentry kind="src" path="src"/>
    <classpathentry kind="src" path="resources"/>
    <classpathentry kind="src" path="test"/>
    <classpathentry kind="con" path="org.eclipse.jdt.launching.JRE_CONTAINER"/>
    <classpathentry kind="lib" path="lib/servlet-api.jar"/>
    <classpathentry kind="lib" path="webapp/WEB-INF/lib/struts2-core-2.1.8.1.jar"/>
         ……
    <classpathentry kind="output" path="webapp/WEB-INF/classes"/>
    </classpath>复制代码

    [类文件的搜索路径: C:\Java\jdk1.7.0_25\jre\lib\resources.jar,C:\Java\jdk1.7.0_25复制代码

    \jre\lib\rt.jar,C:\Java\jdk1.7.0_25\jre\lib\sunrsasign.jar,C:\Java\jdk1.7.0_25\j复制代码

    re\lib\jsse.jar,C:\Java\jdk1.7.0_25\jre\lib\jce.jar,C:\Java\jdk1.7.0_25\jre\lib\复制代码

    charsets.jar,C:\Java\jdk1.7.0_25\jre\lib\jfr.jar,C:\Java\jdk1.7.0_25\jre\classes复制代码

    ,C:\Java\jdk1.7.0_25\jre\lib\ext\access-bridge-32.jar,C:\Java\jdk1.7.0_25\jre\li复制代码

    b\ext\dnsns.jar,C:\Java\jdk1.7.0_25\jre\lib\ext\jaccess.jar,C:\Java\jdk1.7.0_25\复制代码

    jre\lib\ext\localedata.jar,C:\Java\jdk1.7.0_25\jre\lib\ext\sunec.jar,C:\Java\jdk复制代码

    1.7.0_25\jre\lib\ext\sunjce_provider.jar,C:\Java\jdk1.7.0_25\jre\lib\ext\sunmsca复制代码

    pi.jar,C:\Java\jdk1.7.0_25\jre\lib\ext\sunpkcs11.jar,C:\Java\jdk1.7.0_25\jre\lib
    \ext\zipfs.jar,..\bin]             复制代码

    public class A
    {
        public static void main(String[] args) {
            B b = new B();
            b.print();
        }
    }
    
    复制代码

    public class B
    {
        public void print()
        {
            System.out.println("old");
        }
    }
复制代码

|-src
　　　　|-com
　　　　　　|- B.java
　　　　|- A.java
　　|-bin
　　　　|- B.class               //是 B.java复制代码

    javac -classpath bin src/A.java                            //查找到B.class复制代码

    javac -sourcepath src/com src/A.java                   //查找到B.java复制代码

    javac -sourcepath src/com -classpath bin src/A.java    //同时查找到B.class和B.java复制代码

    复制代码

    package com;
    public class Main
    {
        public static void main(String[] args) {
            System.out.println("Hello");
        }
    }
    
    复制代码

    javac -d bin src/com/Main.java复制代码

    public class A
    {
        public static void main(String[] args) {
            B b = new B();
        }
    }复制代码

    public class B
    {
    }复制代码

    如果使用：
    复制代码

     javac -implicit:none A.java复制代码