Question

我正在尝试使用ASM创建一个简单的类文件

我尝试过如下：

    ClassPrinter c = new ClassPrinter();
    ClassReader cr = new ClassReader(new FileInputStream("path/to/class"));
    ClassWriter cw = new ClassWriter(ClassWriter.COMPUTE_MAXS|ClassWriter.COMPUTE_FRAMES);
    cw.newClass("MyClass");
    cw.newField("owner", "value", "I");
    cr.accept(c, 0);
    for(String s : c.values){
        System.out.println(s);
    }
    ClassReader writerReader = new ClassReader(new FileInputStream("C:\\generated.class"));
    writerReader.accept(cw,0);

但是在创建ClassReader时会出现ArrayIndexOutOfBoundsException。

C：\ generated.class现在是一个空文件。

ClassPrinter是一个访问者，它只是遍历所有实体并使用system.out.println打印它们

如何做到这一点？

我需要能够从头创建类，而不仅仅是附加到已有的类。

依赖关系：

<dependency>
    <groupId>org.ow2.asm</groupId>
    <artifactId>asm</artifactId>
    <version>5.0.3</version>
</dependency>

Answer 1

你似乎永远不会写文件“C：\ generated.class”

什么是cr以及代码片段中的c是什么？

在打开阅读器之前，似乎缺少这样的东西：

String filename = "C:\\generated.class"; 

// Generate class

System.out.println("Generating MyClass");
ClassWriter cw = new ClassWriter(ClassWriter.COMPUTE_MAXS|ClassWriter.COMPUTE_FRAMES);
cw.newClass("MyClass");
cw.newField("owner", "value", "I");

// Print generated class to STDIO to see that is generated as expected

System.out.println("Generated:");
ClassPrinter cp = new ClassPrinter();
cp.accept(cw, 0);

// Write the generated class to a file

System.out.println("Writing " + filename);
FileOutputStream os = new FileOutputStream(filename);
os.write(cw.toByteArray());
os.close();

// Read the file back

System.out.println("Reading " + filename);
ClassReader cr = new ClassReader(new FileInputStream("C:\\generated.class"));

// Print the class 

System.out.println("Read");
cr.accept(c, 0);
cr.accept(cw,0);

ASM创建java类

1 个答案: