要比较XACML策略中的两个多元素属性，可以使用XACML的规范和函数库来实现。以下是一个使用Java代码的示例：

import com.sun.xacml.*;
import com.sun.xacml.attr.AttributeValue;
import com.sun.xacml.attr.BagAttribute;
import com.sun.xacml.attr.StringAttribute;
import com.sun.xacml.combine.PolicyCombiningAlgorithm;
import com.sun.xacml.combine.PolicyCombiningAlgorithmFactory;
import com.sun.xacml.combine.RuleCombiningAlgorithm;
import com.sun.xacml.combine.RuleCombiningAlgorithmFactory;
import com.sun.xacml.ctx.*;
import com.sun.xacml.finder.AttributeFinder;
import com.sun.xacml.finder.AttributeFinderModule;
import com.sun.xacml.finder.AttributeFinderResult;
import com.sun.xacml.finder.PolicyFinder;
import com.sun.xacml.finder.PolicyFinderModule;
import com.sun.xacml.finder.PolicyFinderResult;

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

public class XacmlPolicyComparison {

    public static void main(String[] args) throws Exception {
        // 读取策略文件
        PolicySet policySet1 = loadPolicySetFromFile("policySet1.xml");
        PolicySet policySet2 = loadPolicySetFromFile("policySet2.xml");

        // 比较策略
        boolean areEqual = comparePolicySets(policySet1, policySet2);

        if (areEqual) {
            System.out.println("两个策略集合是相等的");
        } else {
            System.out.println("两个策略集合是不相等的");
        }
    }

    private static PolicySet loadPolicySetFromFile(String filePath) throws FileNotFoundException {
        try {
            // 创建XACML解析器
            ConfigurationStore store = new ConfigurationStore();
            PDPConfig pdpConfig = store.getDefaultPDPConfig();

            // 创建策略查找器
            PolicyFinder policyFinder = pdpConfig.getPolicyFinder();

            // 添加策略文件
            policyFinder.addPolicyStore(new PolicyCollection(store));

            // 加载策略集合
            FileInputStream input = new FileInputStream(filePath);
            return (PolicySet) policyFinder.findPolicy(input).getPolicy();
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }

    private static boolean comparePolicySets(PolicySet policySet1, PolicySet policySet2) {
        // 获取策略集合中的策略列表
        List policies1 = policySet1.getChildren();
        List policies2 = policySet2.getChildren();

        // 比较策略数量
        if (policies1.size() != policies2.size()) {
            return false;
        }

        // 比较策略内容
        for (int i = 0; i < policies1.size(); i++) {
            AbstractPolicy policy1 = policies1.get(i);
            AbstractPolicy policy2 = policies2.get(i);

            // 比较策略的Target
            if (!compareTargets(policy1.getTarget(), policy2.getTarget())) {
                return false;
            }

            // 比较策略的规则数量
            if (policy1.getChildren().size() != policy2.getChildren().size()) {
                return false;
            }

            // 比较策略的规则
            for (int j = 0; j < policy1.getChildren().size(); j++) {
                Rule rule1 = (Rule) policy1.getChildren().get(j);
                Rule rule2 = (Rule) policy2.getChildren().get(j);

                // 比较规则的Target
                if (!compareTargets(rule1.getTarget(), rule2.getTarget())) {
                    return false;
                }
            }
        }

        return true;
    }

    private static boolean compareTargets(Target target1, Target target2) {
        // 比较Target中的多元素属性
        Set attrs1 = getMultiElementAttributes(target1);
        Set attrs2 = getMultiElementAttributes(target2);

        // 比较属性数量
        if (attrs1.size() != attrs2.size()) {
            return false;
        }

        // 比较属性内容
        for (String attr : attrs1) {
            if (!attrs2.contains(attr)) {
                return false;
            }
        }