在windows環境下進行的測試，前提條件，windows上需要先安裝openssl。

配置環境變數，檢視版本：

import java.io.*;
import java.util.Properties;

public class OpensslCommand {
  private static void runCMD(String[] CMD) {
    java.lang.Process process = null;
    try {
      process = Runtime.getRuntime().exec(CMD);
      ByteArrayOutputStream resultOutStream = new ByteArrayOutputStream();
      InputStream errorInStream = new BufferedInputStream(process.getErrorStream());
      InputStream processInStream = new BufferedInputStream(process.getInputStream());
      int num = 0;
      byte[] bs = new byte[1024];
      while ((num = errorInStream.read(bs)) != -1) {
        resultOutStream.write(bs,num);
      }
      while ((num = processInStream.read(bs)) != -1) {
        resultOutStream.write(bs,num);
      }
      String result = new String(resultOutStream.toByteArray(),"gbk");
      System.out.println(result);
      errorInStream.close();
      processInStream.close();
      resultOutStream.close();
    } catch (IOException e) {
      e.printStackTrace();
    } finally {
      if (process != null) process.destroy();
    }
  }
  public static void main(String[] args) throws Exception {
    //需要指定openssl.exe路徑
    //java生成私鑰
    String[] cmdPrivateKey = {"cmd","/C","C:\\soft\\OpenSSL-Win64\\bin\\openssl.exe genrsa -out ca.key 2048"};
    //java生成證書請求
    String[] cmdCertificationReq = {"cmd","C:\\soft\\OpenSSL-Win64\\bin\\openssl.exe req -new -key ca.key -out ca.csr -subj /C=CN"};
    //java生成證書
    String[] cmdCertification = {"cmd","C:\\soft\\OpenSSL-Win64\\bin\\openssl.exe x509 -req -days 365 -in ca.csr -signkey ca.key -out ca.crt"};
    runCMD(cmdPrivateKey);
    runCMD(cmdCertificationReq);
    runCMD(cmdCertification);
    Properties props=System.getProperties(); //系統屬性
    System.out.println("使用者的當前工作目錄："+props.getProperty("user.dir"));
  }
}

對應目錄下可以生成：

其中，ca.crt是自簽名證書檔案。ca.key是私鑰。ca.csr只是生成證書的中間請求，是用來指定一些資訊，這邊只指定國家為CN。

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