1，打开eclipse,新建maven工程，在pom中引用jmeter核心jar包，具体请看------，这里就不再赘述

2，代码如下：

package com.mytest.functions;import org.apache.jmeter.engine.util.CompoundVariable;import org.apache.jmeter.functions.AbstractFunction;import org.apache.jmeter.functions.InvalidVariableException;import org.apache.jmeter.samplers.SampleResult;import org.apache.jmeter.samplers.Sampler;import org.apache.jmeter.threads.JMeterVariables;import java.util.Collection;import java.util.LinkedList;import java.util.List;/** * Provides a DoubleSum function that adds two or more Double values. * Mostly copied from LongSum */public class DoubleSum extends AbstractFunction {    private static final List
      
        desc = new LinkedList
       
        ();    private static final String KEY = "__doubleSum";    static {        desc.add("First double to add");        desc.add("Second long to add - further doubles can be summed by adding further arguments");        desc.add("Name of variable in which to store the result (optional),The author is guanyf");    }    private Object[] values;    /**     * No-arg constructor.     */    public DoubleSum() {    }    /**     * {
     @inheritDoc}     */    @Override    public synchronized String execute(SampleResult previousResult, Sampler currentSampler)            throws InvalidVariableException {        JMeterVariables vars = getVariables();        Double sum = 0D;        String varName = ((CompoundVariable) values[values.length - 1]).execute().trim();        for (int i = 0; i < values.length - 1; i++) {            sum += Double.parseDouble(((CompoundVariable) values[i]).execute());        }        try {            sum += Double.parseDouble(varName);            varName = null; // there is no variable name        } catch (NumberFormatException ignored) {        }        String totalString = Double.toString(sum);        if (vars != null && varName != null && varName.length() > 0) {
    // vars will be null on TestPlan            vars.put(varName, totalString);        }        return totalString;    }    /**     * {
     @inheritDoc}     */    @Override    public synchronized void setParameters(Collection
        
          parameters) throws InvalidVariableException {        checkMinParameterCount(parameters, 2);        values = parameters.toArray();    }    /**     * {
     @inheritDoc}     */    @Override    public String getReferenceKey() {        return KEY;    }    /**     * {
     @inheritDoc}     */    @Override    public List
         
           getArgumentDesc() {        return desc;    }}