使用Asm字节码生成器（ClassWriter）生成具有泛型类型的方法

问题描述

定义简单的getter和setter很容易使用Asm（幸运的是，它甚至可以在他们的FAQ中解释）。但有一件事没有提到，而我一直无法找到文档，是如何使用泛型类型信息来实现这些。

我实际上可以确定泛型类型信息本身很容易（因为代码将采用现有的字段和/或方法，并且存在完整的泛型类型处理和分辨率）。我只需要为包含泛型类型的类型生成泛型版本。

我希望这与修改Asm ClassWriter / MethodVisitor调用的签名一样简单，但一些注释在文档中指出它可能并不那么容易（因为泛型信息与常规信息存储在不同的位置）。

编辑：看起来像入口点是ClassWriter.visitField / Method（....，String signature） - 注意它是包含正常非泛型类信息的描述，但术语签名（在JLS中）具体指的是泛型 - 包括类型信息。

解决方案

您可以使用ASM的 class。

例如，假设您希望为此方法编写签名：

  public< K>你可以使用下面的代码：
 
 
 
 
 
 $ b 
 b $ b 
  SignatureWriter签名= new SignatureWriter（）; 
 signature.visitFormalTypeParameter（K）; 
 
 //确保< K> extends java.lang.Object 
 {
 SignatureVisitor classBound = signature.visitClassBound（）; 
 classBound.visitClassType（Type.getInternalName（Object.class））; 
 classBound.visitEnd（）; 
} 
 
 //该参数使用< K>类型变量
 signature.visitParameterType（）。visitTypeVariable（K）; 
 
 //返回类型使用void原语（'V'）
 signature.visitReturnType（）。visitBaseType（'V'）; 
 
 signature.visitEnd（）; 
 
 String signatureString = signature.toString（）; 
  
相当于： 
 
 
  String signatureString =< K：Ljava / lang / Object;>（TK;）V; 
  
 
Defining simple getters and setters is easy using Asm (and fortunately it is even explained in their FAQ). But one thing that is not mentioned, and for which I have been unable to find documentation, is how to implement these using generic type information.
I am actually able to determine generic type information itself quite easily (since code will take existing fields and/or methods and full generic type handling and resolution exists). I just need to generate generics version for types that have generic type included.
I hope this is something as easy as modifying signature Asm ClassWriter/MethodVisitor calls take, but some comments in documentation indicate it might not be that easy (as generics information is stored in bit different place than regular info).
EDIT: looks like entry point is "ClassWriter.visitField/Method(...., String signature) -- note that it's "description" that contains normal non-generic class information, but term "signature" (in JLS) specifically refers to generics-including type information. 
 解决方案 
You can build the signature using ASM's SignatureWriter class.
For example, suppose you wish to write the signature for this method:
public <K> void doSomething(K thing)
You could use this code:
SignatureWriter signature = new SignatureWriter();
signature.visitFormalTypeParameter("K");

// Ensure that <K> extends java.lang.Object
{
    SignatureVisitor classBound = signature.visitClassBound();
    classBound.visitClassType(Type.getInternalName(Object.class));
    classBound.visitEnd();
}

// The parameter uses the <K> type variable
signature.visitParameterType().visitTypeVariable("K");

// The return type uses the void primitive ('V')
signature.visitReturnType().visitBaseType('V');

signature.visitEnd();

String signatureString = signature.toString();
Which is equivalent to:
String signatureString = "<K:Ljava/lang/Object;>(TK;)V;"
                        
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