Example usage for org.springframework.asm MethodVisitor visitInsn

Introduction

In this page you can find the example usage for org.springframework.asm MethodVisitor visitInsn.

Prototype

public void visitInsn(final int opcode) 

Source Link

Document

Visits a zero operand instruction.

Usage

From source file:org.springframework.expression.spel.standard.SpelCompiler.java

/**
 * Generate the class that encapsulates the compiled expression and define it.
 * The  generated class will be a subtype of CompiledExpression.
 * @param expressionToCompile the expression to be compiled
 * @return the expression call, or {@code null} if the decision was to opt out of
 * compilation during code generation//from  ww w. ja v  a 2  s .  c om
 */
@Nullable
private Class<? extends CompiledExpression> createExpressionClass(SpelNodeImpl expressionToCompile) {
    // Create class outline 'spel/ExNNN extends org.springframework.expression.spel.CompiledExpression'
    String clazzName = "spel/Ex" + getNextSuffix();
    ClassWriter cw = new ExpressionClassWriter();
    cw.visit(V1_5, ACC_PUBLIC, clazzName, null, "org/springframework/expression/spel/CompiledExpression", null);

    // Create default constructor
    MethodVisitor mv = cw.visitMethod(ACC_PUBLIC, "<init>", "()V", null, null);
    mv.visitCode();
    mv.visitVarInsn(ALOAD, 0);
    mv.visitMethodInsn(INVOKESPECIAL, "org/springframework/expression/spel/CompiledExpression", "<init>", "()V",
            false);
    mv.visitInsn(RETURN);
    mv.visitMaxs(1, 1);
    mv.visitEnd();

    // Create getValue() method
    mv = cw.visitMethod(ACC_PUBLIC, "getValue",
            "(Ljava/lang/Object;Lorg/springframework/expression/EvaluationContext;)Ljava/lang/Object;", null,
            new String[] { "org/springframework/expression/EvaluationException" });
    mv.visitCode();

    CodeFlow cf = new CodeFlow(clazzName, cw);

    // Ask the expression AST to generate the body of the method
    try {
        expressionToCompile.generateCode(mv, cf);
    } catch (IllegalStateException ex) {
        if (logger.isDebugEnabled()) {
            logger.debug(expressionToCompile.getClass().getSimpleName()
                    + ".generateCode opted out of compilation: " + ex.getMessage());
        }
        return null;
    }

    CodeFlow.insertBoxIfNecessary(mv, cf.lastDescriptor());
    if ("V".equals(cf.lastDescriptor())) {
        mv.visitInsn(ACONST_NULL);
    }
    mv.visitInsn(ARETURN);

    mv.visitMaxs(0, 0); // not supplied due to COMPUTE_MAXS
    mv.visitEnd();
    cw.visitEnd();

    cf.finish();

    byte[] data = cw.toByteArray();
    // TODO need to make this conditionally occur based on a debug flag
    // dump(expressionToCompile.toStringAST(), clazzName, data);
    return loadClass(clazzName.replaceAll("/", "."), data);
}

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