要加载多个密钥库，您可以使用Apache HttpClient的SSLContextBuilder类。以下是一个示例代码：

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.client.methods.HttpUriRequest;
import org.apache.http.conn.ssl.SSLContextBuilder;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.util.EntityUtils;

import javax.net.ssl.SSLContext;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.security.KeyStore;

public class HttpClientExample {

    public static void main(String[] args) throws Exception {
        // 设置密钥库和信任库的路径和密码
        String keyStorePath1 = "/path/to/keystore1.jks";
        String keyStorePassword1 = "keystore1_password";
        
        String keyStorePath2 = "/path/to/keystore2.jks";
        String keyStorePassword2 = "keystore2_password";
        
        String trustStorePath = "/path/to/truststore.jks";
        String trustStorePassword = "truststore_password";

        // 加载第一个密钥库
        KeyStore keyStore1 = KeyStore.getInstance(KeyStore.getDefaultType());
        try (FileInputStream fis = new FileInputStream(new File(keyStorePath1))) {
            keyStore1.load(fis, keyStorePassword1.toCharArray());
        }

        // 加载第二个密钥库
        KeyStore keyStore2 = KeyStore.getInstance(KeyStore.getDefaultType());
        try (FileInputStream fis = new FileInputStream(new File(keyStorePath2))) {
            keyStore2.load(fis, keyStorePassword2.toCharArray());
        }

        // 加载信任库
        KeyStore trustStore = KeyStore.getInstance(KeyStore.getDefaultType());
        try (FileInputStream fis = new FileInputStream(new File(trustStorePath))) {
            trustStore.load(fis, trustStorePassword.toCharArray());
        }

        // 创建SSL上下文，将密钥库和信任库添加到SSL上下文
        SSLContext sslContext = SSLContextBuilder.create()
                .loadKeyMaterial(keyStore1, keyStorePassword1.toCharArray())
                .loadKeyMaterial(keyStore2, keyStorePassword2.toCharArray())
                .loadTrustMaterial(trustStore)
                .build();

        // 创建HttpClient，并设置SSL上下文
        CloseableHttpClient httpClient = HttpClients.custom()
                .setSSLContext(sslContext)
                .build();

        // 发送请求
        HttpUriRequest request = new HttpGet("https://example.com");
        HttpResponse response = httpClient.execute(request);

        // 处理响应
        HttpEntity entity = response.getEntity();
        String responseBody = EntityUtils.toString(entity);
        System.out.println(responseBody);

        // 关闭HttpClient
        httpClient.close();
    }
}

在上面的示例代码中，您需要将keyStorePath1，keyStorePassword1，keyStorePath2，keyStorePassword2，trustStorePath和trustStorePassword替换为您自己的密钥库和信任库的路径和密码。请确保您的密钥库和信任库文件存在并且具有正确的访问权限。

在SSLContextBuilder.create()中，使用loadKeyMaterial()方法加载每个密钥库，并使用loadTrustMaterial()方法加载信任库。最后，使用build()方法构建SSL上下文。最后，将SSL上下文设置到HttpClient中，以便使用加载的密钥库和信任库进行HTTPS请求。