在Camunda中，有四种方法来声明如何调用JAVA逻辑:

1. 指定实现JavaDelegate或ActivityBehavior的类
2. 计算解析为委托对象的表达式
3. 调用方法表达式
4. 求值表达式的值

本文重点描述基于JavaDelegate配置Camunda 的自动化服务节点，在JavaDelegate实现类里完成逻辑计算，并把计算结果返回给流程变量。

一、设计流程图

要指定在进程执行期间调用的类，camunda:class属性需要提供完全限定的类名。要实现可以在流程执行期间调用的类，这个类需要实现
org.camunda.bpm.engine.delegate.JavaDelegate接口，并在execute方法中提供所需的逻辑。当流程执行到达这个特定的步骤时，它将执行该方法中定义的逻辑，并以默认的BPMN 2.0方式保留活动。

作为示例，让我们创建一个Java类，实现里模拟业务逻辑。这个类需要实现
org.camunda.bpm.engine.delegate.JavaDelegate接口，它需要我们实现execute(DelegateExecution)方法。引擎将调用这个操作，并且需要包含业务逻辑。流程实例信息(如流程变量和其他信息)可以通过DelegateExecution接口访问和操作。

JavaDelegate示例实现类：

package com.example.demo1;import org.camunda.bpm.engine.delegate.DelegateExecution;import org.camunda.bpm.engine.delegate.JavaDelegate;/** * 贷款计算类 */public class LoanDelegate  implements JavaDelegate {    @Override    public void execute(DelegateExecution delegateExecution) throws Exception {        Double yearWages = (Double) delegateExecution.getVariable("yearWages");        Double houseAssets = (Double) delegateExecution.getVariable("houseAssets");        double sum = yearWages + houseAssets;        if(sum<=0){            delegateExecution.setVariable("creditRating","C");            delegateExecution.setVariable("loanLimit",0);        }else  if(sum>0 && sum <=100){            delegateExecution.setVariable("creditRating","B");            delegateExecution.setVariable("loanLimit",sum*0.8);        }else  if(sum>100){            delegateExecution.setVariable("creditRating","A");            delegateExecution.setVariable("loanLimit",sum*1.2);        }    }}

以下是完整的BPMN模型文件：

<?xml version="1.0" encoding="UTF-8"?><bpmn:definitions xmlns:bpmn="http://www.omg.org/spec/BPMN/20100524/MODEL" xmlns:bpmndi="http://www.omg.org/spec/BPMN/20100524/DI" xmlns:dc="http://www.omg.org/spec/DD/20100524/DC" xmlns:camunda="http://camunda.org/schema/1.0/bpmn" xmlns:di="http://www.omg.org/spec/DD/20100524/DI" xmlns:modeler="http://camunda.org/schema/modeler/1.0" id="Definitions_1wr7a1v" targetNamespace="http://bpmn.io/schema/bpmn" exporter="Camunda Modeler" exporterVersion="4.8.1" modeler:executionPlatform="Camunda Platform" modeler:executionPlatformVersion="7.15.0">  <bpmn:process id="Process_0a6gw7u" name="贷款申请流程Java" isExecutable="true">    <bpmn:startEvent id="StartEvent_1">      <bpmn:outgoing>Flow_0kzdck2</bpmn:outgoing>    </bpmn:startEvent>    <bpmn:sequenceFlow id="Flow_0kzdck2" sourceRef="StartEvent_1" targetRef="Activity_1l6o8wm" />    <bpmn:sequenceFlow id="Flow_0h8bikl" sourceRef="Activity_1l6o8wm" targetRef="Activity_1wjgiji" />    <bpmn:userTask id="Activity_1wjgiji" name="确认贷款额度" camunda:assignee="demo">      <bpmn:incoming>Flow_0h8bikl</bpmn:incoming>      <bpmn:outgoing>Flow_03h3srs</bpmn:outgoing>    </bpmn:userTask>    <bpmn:sequenceFlow id="Flow_03h3srs" sourceRef="Activity_1wjgiji" targetRef="Event_0myx83u" />    <bpmn:endEvent id="Event_0myx83u">      <bpmn:incoming>Flow_03h3srs</bpmn:incoming>    </bpmn:endEvent>    <bpmn:serviceTask id="Activity_1l6o8wm" name="计算贷款额度" camunda:class="com.example.demo1.LoanDelegate">      <bpmn:incoming>Flow_0kzdck2</bpmn:incoming>      <bpmn:outgoing>Flow_0h8bikl</bpmn:outgoing>    </bpmn:serviceTask>  </bpmn:process>  <bpmndi:BPMNDiagram id="BPMNDiagram_1">    <bpmndi:BPMNPlane id="BPMNPlane_1" bpmnElement="Process_0a6gw7u">      <bpmndi:BPMNEdge id="Flow_03h3srs_di" bpmnElement="Flow_03h3srs">        <di:waypoint x="600" y="117" />        <di:waypoint x="692" y="117" />      </bpmndi:BPMNEdge>      <bpmndi:BPMNEdge id="Flow_0h8bikl_di" bpmnElement="Flow_0h8bikl">        <di:waypoint x="390" y="117" />        <di:waypoint x="500" y="117" />      </bpmndi:BPMNEdge>      <bpmndi:BPMNEdge id="Flow_0kzdck2_di" bpmnElement="Flow_0kzdck2">        <di:waypoint x="215" y="117" />        <di:waypoint x="290" y="117" />      </bpmndi:BPMNEdge>      <bpmndi:BPMNShape id="_BPMNShape_StartEvent_2" bpmnElement="StartEvent_1">        <dc:Bounds x="179" y="99" width="36" height="36" />      </bpmndi:BPMNShape>      <bpmndi:BPMNShape id="Activity_187in45_di" bpmnElement="Activity_1wjgiji">        <dc:Bounds x="500" y="77" width="100" height="80" />      </bpmndi:BPMNShape>      <bpmndi:BPMNShape id="Event_0myx83u_di" bpmnElement="Event_0myx83u">        <dc:Bounds x="692" y="99" width="36" height="36" />      </bpmndi:BPMNShape>      <bpmndi:BPMNShape id="Activity_05149db_di" bpmnElement="Activity_1l6o8wm">        <dc:Bounds x="290" y="77" width="100" height="80" />      </bpmndi:BPMNShape>    </bpmndi:BPMNPlane>  </bpmndi:BPMNDiagram></bpmn:definitions>

二、发起流程测试

登录：
http://localhost:8080/camunda/App/admin/default/#/login

1、发起流程，输入流程变量，后面的Java代理节点计算需要这两个流程变量

2、提交流程后，查看流程图，Java代理节点已经成功执行了

3、查看表单中的流程变量，Java代理节点计算后的返回值已经成功写入了。

更多参考：

Service Task | docs.camunda.org