2-《Java并发编程实战》(Java Concurrency in Practice) 代码示例

说明

这是针对《Java并发编程实战》(Java Concurrency in Practice)一书中的示例代码进行扩展，并且进行验证的完整代码，具体背景可看这篇文章：1-《Java并发编程实战》(Java Concurrency in Practice) 代码示例

下面的示例代码都是针对书中的（不完整的）代码扩展，不再介绍具体上下文背景（如果你也在看这本书，可以拿我这里的示例代码做个参考，并欢迎提出意见和建议）

程序清单2-5

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
import java.math.BigInteger;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.concurrent.atomic.AtomicReference;

/**
 * @DESCRIPTION:
 * @USER: shg
 * @DATE: 2024/1/13 11:15
 */
public class UnsafeCachingFactorizer extends HttpServlet {

    private final AtomicReference<BigInteger> lastNumber = new AtomicReference<>();
    private final AtomicReference<BigInteger[]> lastFactors = new AtomicReference<>();

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        BigInteger i = extractFromRequest(req);
        if (i.equals(lastNumber.get())) {
            encodeIntoResponse(resp, i, lastFactors.get());
        } else {
            BigInteger[] factors = factor(i);
            lastNumber.set(i);
            lastFactors.set(factors);
            encodeIntoResponse(resp, i, lastFactors.get());
        }
    }

    private BigInteger extractFromRequest(HttpServletRequest req) {
        return new BigInteger(req.getParameter("key"));
    }

    private void encodeIntoResponse(HttpServletResponse resp, BigInteger i, BigInteger[] factors) throws IOException {
        System.out.println(i + "--->" + Arrays.asList(factors));
        resp.setContentType("text/html;charset=utf-8");
        PrintWriter writer = resp.getWriter();
        writer.println("<html><body>");
        writer.println("<h1>" + i + "因数分解结果为：" + Arrays.asList(factors));
        writer.println("</body></html>");
    }

    private BigInteger[] factor(BigInteger number) {
        List<BigInteger> factors = new ArrayList<>();
        BigInteger divisor = BigInteger.valueOf(2);
        while (number.compareTo(BigInteger.ONE) > 0) {
            if (number.mod(divisor).equals(BigInteger.ZERO)) {
                number = number.divide(divisor);
                factors.add(divisor);
            } else {
                divisor = divisor.add(BigInteger.ONE);
            }
        }
        return factors.toArray(new BigInteger[0]);
    }
}