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README
EPL-1.0

kan-java

'kan-java' is '砍-java', speak frankly & literally.

这是一个java代码动态编译工具,也就是能够把String形式的java代码实时地编译为字节码的工具;

“动态编译”工具,其实自jdk1.6发布以来,应该出现过很多,不过kan-java的特点在于 —— 就像它的名字一样 —— 可以选择性地砍掉任意语言特性;

也就是说 —— 这是一个可以在动态编译java代码的同时,对java语言语法做裁剪的动态编译工具。

通过下面这个例子可以看出“裁剪”指的是什么意思:

// 禁止带标签的continue语句
void testLabeledContinue(){
    def kan = new KanJava(Feature.labeledContinue)
    def srcs = []
    srcs << new JavaSourceFile("TestLabeledContinue.java", "kanjava.test", readContent("testLabeledContinue/TestLabeledContinue.src"));
    def rst = kan.checkAndCompile(srcs)

    assertTrue !rst.isSuccess()
    assertTrue rst.errMsg != null
    assertTrue rst.classes == null
    println rst.errMsg
}

上述groovy代码创建了一个KanJava编译工具实例, 并指明想要砍掉labeledContinue特性(即带标签的continue语句)
其中readContent方法的返回结果如下:

package kanjava.test;

public class TestLabeledContinue {

    public static void main(String... args) {
        for(int i=0;i<10;i++){
            if(i == 5) continue;
        }
        label: while(true){
            if(true) continue label;
        }
    }
}

上述代码包含2个continue语句:第一个不带标签而第二个带标签
最终输出结果如下:

Error at row: 10, col: 22, reason: Continue statements with labels are not allowed.

即“带标签的continue语句”已被禁止了,在编译过程中发现这种语句即会报错, 其核心功能,概念上讲就是这么简单。

这能有什么用?

拥有一个裁剪版本的java,这有怎样的应用场景?

目前最直接的答案是"高性能的内部DSL"

即当我需要一个语法上非常接近普通过程式编程语言的DSL,但却又不想或觉得没必要自己从头实现一个(外部DSL)的时候,就可以考虑以某种现成的过程式通用编程语言为蓝本,通过裁剪其语法达到目的;
而当这种“现成的过程式通用编程语言”被选择为java时,kan-java出场的时刻就到了, 试想一下,下面这样“砍”会砍出来什么效果? ——

private static final KanJava kanJava = new KanJava(Feature.assertion, 
                                                   Feature.doWhileLoop,
                                                   Feature.forLoop,
                                                   Feature.labeledBreak,
                                                   Feature.labeledContinue,
                                                   Feature.nestedClass,
                                                   Feature.whileLoop);

相信所有java程序员都可以猜到:你将得到一个“没有assert语句、没有do-while循环、没有for循环、没有带标签的break、没有带标签的continue、没有嵌套类、没有while循环”的 —— java.
P.S. 如果你还坚信它是java的话 :)

而这些"内部DSL"最终将被编译成字节码运行,因此也有了高速运行的基础;
所以说kan-java能够成为“利用java实现高性能的内部DSL”的强大工具。

上面示例中的这种“砍”法并不夸张,这是从现实中的使用案例中截选出来的。

一些更实用 & 更高级的功能

kan-java提供的api能够将“砍语法”和“编译为字节码”拆分为两个步骤;
这使得你可以 —— 比如说 —— 在用户输入的时候禁掉'import语句',而实际编译的时候可以正常插入import语句后再编译, 相信这种功能会很有用;

更普遍意义地讲,kan-java实际上提供了一套"java语言语法静态处理框架", 在此框架之上,“砍”语法其实只是冰山一角 —— 因为你还可以用它来“砍用法”,比如你并不想完全禁掉import语句,但希望禁止import一些特定的类;
再比如你不想完全禁止用户new对象,但你能够做到不让用户new特定的对象...

凡是能够出现在代码当中的任意结构,都可以被控制。
因此可以说,被发布出来的kan-java库只是一个小小的核心,其更加广阔的应用场景还有待猿们继续扩充...

有没有更加“高级(黑)”的话题? 当然有;因为在kan-java提供的这套框架之上不仅限于能“砍”,它还能“加”...
不过目前这个库的主要目的还是提供一套“基于java的内部DSL构建工具”,其它的什么“用kan-java做源码增强”,什么“用kan-java把java编译到GPU上”这些黑科技就暂不展开了 :)

注意事项

最重要的事情总是最后才说...

目前kan-java所支持的java基础语法是1.6的,也就是说,你使用kan-java来“砍”语法的时候,是以java 1.6为基础来砍的
不过这并不影响kan-java库被放到更高版本的java环境中使用(above v1.6), 起码大多数情况下是ok的;不过,如果真的遇到问题,还是最好能从源码编译一份对应当前java版本环境的kan-java库(因为kan-java在实现上使用了com.sun包下的一些类, 这些类并不完全保证在不同版本java之间的兼容)

同样因为kan-java使用了com.sun包下的类,我也只能假定kan-java只能在oracle jvm上运行

目前开放的可被“砍”的功能,只是源于目前我个人在实际项目中的需要而已;肯定还有更多可能的“花式砍法”,如果希望有,可以提出来,有兴趣的我们可以共建

使用kan-java时,需确保tools.jar也在classpath中

按道理讲,除了java标准库,kan-java是不需要依赖任何第三方库的,不过项目中出现了对groovy-all的依赖,这仅仅是因为我想实践一把"java和groovy混编开发模式"的任性而已,不要太在意 :)

目前的发布版本及maven依赖方式详见:Releases

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简介

A dynamic compilation tool for java which also allows you to cut language features. 展开 收起
Java
EPL-1.0
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