Example usage for org.springframework.asm MethodVisitor visitMaxs

Introduction

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

Prototype

public void visitMaxs(final int maxStack, final int maxLocals) 

Source Link

Document

Visits the maximum stack size and the maximum number of local variables of the method.

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  w  w w  .  jav a2s  .c o m
 */
@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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