Very simple bytecode generation library for Go
- Creating Java classes, methods and global fields
- Jump labels/instructions
- Automatic stack depth calculation
- Automatic locals calculation
- Efficient generation
- Low-level access
- Simple and self-documented codebase
- Constant pool caching
- Annotation support
LineNumberTablesupport- Exception support (
throws) - Inner classes
- Stack frames
package main
import (
"fmt"
"github.com/SocketByte/bytecode"
)
func main() {
// Create new Java class
visitor := bytecode.NewClass(bytecode.Java5,
"my/package/HelloWorld", "java/lang/Object", []string{"java/lang/Cloneable"},
bytecode.AccPublic|bytecode.AccSuper)
// Add source file attribute
visitor.AddSourceFile("HelloWorld.java")
// Append 2 global fields
visitor.NewField(bytecode.AccPublic|bytecode.AccFinal,
"globalValue", "I", 43)
visitor.NewField(bytecode.AccPublic,
"globalString", "Ljava/lang/String;", nil)
// Create new basic constructor
init := visitor.NewMethod(bytecode.AccPublic, "<init>", "()V")
init.AddInsn(bytecode.Aload0)
init.AddMethodInsn(bytecode.Invokespecial,
"java/lang/Object", "<init>", "()V")
init.AddInsn(bytecode.Return)
// This also requires the Cloneable.clone method to be generated!
clone := visitor.NewMethod(bytecode.AccPublic, "clone", "()Lmy/package/HelloWorld;")
clone.AddTypeInsn(bytecode.New, "my/package/HelloWorld")
clone.AddInsn(bytecode.Dup)
clone.AddMethodInsn(bytecode.Invokespecial,
"my/package/HelloWorld", "<init>", "()V")
clone.AddInsn(bytecode.Areturn)
// Create main method
main := visitor.NewMethod(bytecode.AccPublic|bytecode.AccStatic|bytecode.AccVarargs,
"main", "([Ljava/lang/String;)V")
// Push -3 as byte value
main.AddInt8Insn(bytecode.Bipush, -3)
// Store at 1
main.AddVarInsn(bytecode.Istore1)
// Load 1
main.AddInsn(bytecode.Iload1)
// Push 2 as int value
main.AddInsn(bytecode.Iconst2)
// Create a new jump label
label := main.NewLabel()
// Add jump instruction (control-flow) to a newly created label
main.AddJumpInsn(bytecode.Ificmpge, label)
// System.out.println("Hello, World!");
main.AddFieldInsn(bytecode.Getstatic, "java/lang/System", "out", "Ljava/io/PrintStream;")
main.AddLdcInsn("Hello, World!")
main.AddMethodInsn(bytecode.Invokevirtual,
"java/io/PrintStream", "println", "(Ljava/lang/String;)V")
// Add return to the method
main.AddInsn(bytecode.Return)
// Set label to point to "return" instruction (jump to return)
main.AddLabel(label)
fmt.Println(visitor.AsBytecode())
}public class my.package.HelloWorld implements java.lang.Cloneable
minor version: 0
major version: 49
flags: (0x0021) ACC_PUBLIC, ACC_SUPER
this_class: #10 // my/package/HelloWorld
super_class: #4 // java/lang/Object
interfaces: 1, fields: 2, methods: 3, attributes: 1
Constant pool:
#1 = Utf8 SourceFile
#2 = Utf8 HelloWorld.java
#3 = Utf8 java/lang/Object
#4 = Class #3 // java/lang/Object
#5 = Utf8 <init>
#6 = Utf8 ()V
#7 = NameAndType #5:#6 // "<init>":()V
#8 = Methodref #4.#7 // java/lang/Object."<init>":()V
#9 = Utf8 my/package/HelloWorld
#10 = Class #9 // my/package/HelloWorld
#11 = Methodref #10.#7 // my/package/HelloWorld."<init>":()V
#12 = Utf8 java/lang/System
#13 = Class #12 // java/lang/System
#14 = Utf8 out
#15 = Utf8 Ljava/io/PrintStream;
#16 = NameAndType #14:#15 // out:Ljava/io/PrintStream;
#17 = Fieldref #13.#16 // java/lang/System.out:Ljava/io/PrintStream;
#18 = Utf8 Hello, World!
#19 = String #18 // Hello, World!
#20 = Utf8 java/io/PrintStream
#21 = Class #20 // java/io/PrintStream
#22 = Utf8 println
#23 = Utf8 (Ljava/lang/String;)V
#24 = NameAndType #22:#23 // println:(Ljava/lang/String;)V
#25 = Methodref #21.#24 // java/io/PrintStream.println:(Ljava/lang/String;)V
#26 = Utf8 java/lang/Cloneable
#27 = Class #26 // java/lang/Cloneable
#28 = Utf8 Code
#29 = Utf8 clone
#30 = Utf8 ()Lmy/package/HelloWorld;
#31 = Utf8 main
#32 = Utf8 ([Ljava/lang/String;)V
#33 = Utf8 globalValue
#34 = Utf8 I
#35 = Integer 43
#36 = Utf8 ConstantValue
#37 = Utf8 globalString
#38 = Utf8 Ljava/lang/String;
{
public final int globalValue;
descriptor: I
flags: (0x0011) ACC_PUBLIC, ACC_FINAL
ConstantValue: int 43
public java.lang.String globalString;
descriptor: Ljava/lang/String;
flags: (0x0001) ACC_PUBLIC
public my.package.HelloWorld();
descriptor: ()V
flags: (0x0001) ACC_PUBLIC
Code:
stack=1, locals=1, args_size=1
0: aload_0
1: invokespecial #8 // Method java/lang/Object."<init>":()V
4: return
public my.package.HelloWorld clone();
descriptor: ()Lmy/package/HelloWorld;
flags: (0x0001) ACC_PUBLIC
Code:
stack=2, locals=1, args_size=1
0: new #10 // class my/package/HelloWorld
3: dup
4: invokespecial #11 // Method "<init>":()V
7: areturn
public static void main(java.lang.String...);
descriptor: ([Ljava/lang/String;)V
flags: (0x0089) ACC_PUBLIC, ACC_STATIC, ACC_VARARGS
Code:
stack=2, locals=2, args_size=1
0: bipush -3
2: istore_1
3: iload_1
4: iconst_2
5: if_icmpge 16
8: getstatic #17 // Field java/lang/System.out:Ljava/io/PrintStream;
11: ldc #19 // String Hello, World!
13: invokevirtual #25 // Method java/io/PrintStream.println:(Ljava/lang/String;)V
16: return
}
SourceFile: "HelloWorld.java"