Java Servlet 方法参数、响应和线程安全

Question

我在 Tomcat 上使用 Java Servlet 编写了一些 REST API。这是我第一次接触 Java、API 和 Tomcat。当我研究和阅读有关 servlet、方法和参数传递以及最近的线程安全性的内容时，我意识到我需要来自那些我认为更有经验的人的一些评论、建议和教程指导。我发现了许多问题/答案，这些问题/答案似乎都能解决问题，但我缺乏经验，无法实现我想要的清晰度。

下面的代码显示了一个 servlet 示例的顶部部分以及一个示例私有(private)方法。我在类级别定义了“全局”变量，以便我可以跟踪方法的成功并确定是否需要发送错误响应。我这样做是因为方法已经返回一个值。

1. 这些全局变量是否会创建不安全的线程环境
2. 由于响应在私有(private)方法中不可见，如果这些全局变量不安全，我该如何确定是否需要停止进程并发送错误响应
3. 虽然节省了空间，但我是否应该在 doGet 方法中执行所有 XML 处理
4. 我是否应该为各种数据检索任务和数据处理调用所有不同的私有(private)方法
5. 访问同一数据库的每个方法都应该打开一个连接，还是 doGet 方法创建一个连接并将其传递给每个方法

协助、建议、教导、指导您认为合适的任何事情，或者为我指出正确的学习资源，以便我可以学习如何做得更好。欢迎直接和建设性的批评——不喜欢攻击和贬损的言论。

@WebServlet(name = "SubPlans", urlPatterns = {"*omitted*"})
public class SubPlans extends HttpServlet {

  private transient ServletConfig servletConfig;
  private String planSpecialNotes,
      planAddlReqLinks,
      legalTermsHeader,
      legalTermsMemo,
      httpReturnMsg;
  private String[] subPlanInd = new String[4];
  private boolean sc200;
  private int httpReturnStatus;

  private static final long serialVersionUID = 1L;

  {
    httpReturnStatus = 0;
    httpReturnMsg = "";
    sc200 = true;
    planAddlReqLinks = null;
    planSpecialNotes = null;
    legalTermsHeader = "";
    legalTermsMemo = null;
  }

  @Override
  public void init(ServletConfig servletConfig)
      throws ServletException {
    this.servletConfig = servletConfig;
  }

  @Override
  public ServletConfig getServletConfig() {
    return servletConfig;
  }

  @Override
  public String getServletInfo() {
    return "SubPlans";
  }

  @Override
  public void doGet(HttpServletRequest request, HttpServletResponse   response)
      throws ServletException, IOException {
    List<HashMap<String, Object>> alSubDeps = new ArrayList<HashMap<String, Object>>();
    String[] coverageDates = new String[6],
        depDates = new String[8];
    String eeAltId = null,
        eeSSN = null,
        carrier = null,
        logosite = null,
        fmtSSN = "X",
        subSQL = null,
        healthPlan = null,
        dentalPlan = null,
        visionPlan = null,
        lifePlan = null,
        tier = null,
        healthGroupNum = null,
        effdate = null,
        holdEffDate = null,
        planDesc = "",
        planYear = "",
        summaryBenefitsLink = null;
    int[][] effdates = new int[6][4];
    int holdDistrictNumber = 0,
        districtNumber = 0,
        holdUnit = 0,
        unit = 0;
    boolean districtHasHSA = false;
    XMLOutputFactory outputFactory = XMLOutputFactory.newInstance();
    try {
      eeAltId = request.getParameter("*omitted*");
      if ( eeAltId != null ) {
        Pattern p = Pattern.compile(*omitted*);
        Matcher m = p.matcher(eeAltId);
        if ( m.find(0) ) {
          eeSSN = getSSN(eeAltId);
        } else {
          httpReturnStatus = 412;
          httpReturnMsg = "Alternate ID format incorrect.";
          System.err.println("Bad alternate id format " + eeAltId);
          sc200 = false;
        }
      } else {
        httpReturnStatus = 412;
        httpReturnMsg = "Alternate ID missing.";
        System.err.println("alternate id not provided.");
        sc200 = false;
      }
      if ( sc200 ) {
        coverageDates = determineDates();
        subSQL = buildSubSQLStatement(eeSSN, coverageDates);
        alSubDeps = getSubDeps(subSQL);
        if ( sc200 ) {
          XMLStreamWriter writer = outputFactory.createXMLStreamWriter(response.getOutputStream());
          writer.writeStartDocument("1.0");
          writer.writeStartElement("subscriber");
     //  CLIPPED //
          writer.writeEndElement();   // subscriber
          writer.writeEndDocument();
          if ( sc200 ) {
            response.setStatus(HttpServletResponse.SC_OK);
            writer.flush();
          } else {
            response.sendError(httpReturnStatus, httpReturnMsg);
          }
        }
      }
    } catch (Exception e) {
      e.printStackTrace();
      System.err.println("Error writing XML");
      System.err.println(e);
    }
  }
  @Override
  public void destroy() {

  }

  private String getPlanDescription(String planID) {
    String planDesc = null;
    String sqlEE = "SELECT ...";
    Connection connGPD = null;
    Statement stGPD = null;
    ResultSet rsGPD = null;
    try {
      connGPD = getDbConnectionEE();
      try {
        stGPD = connGPD.createStatement();
        planDesc = "Statement error";
        try {
          rsGPD = stGPD.executeQuery(sqlEE);
          if ( !rsGPD.isBeforeFirst() )
            planDesc = "No data";
          else {
            rsGPD.next();
            planDesc = rsGPD.getString("Plan_Description");
          }
        } catch (Exception rsErr) {
          httpReturnStatus = 500;
          httpReturnMsg = "Error retrieving plan description.";
          System.err.println("getPlanDescription: " + httpReturnMsg + " " + httpReturnStatus);
          System.err.println(rsErr);
          sc200 = false;
        } finally {
          if ( rsGPD != null ) {
            try {
              rsGPD.close();
            } catch (Exception rsErr) {
              System.err.println("getPlanDescription: Error closing result set.");
              System.err.println(rsErr);
            }
          }
        }
      } catch (Exception stErr) {
        httpReturnStatus = 500;
        httpReturnMsg = "Error creating plan description statement.";
        System.err.println("getPlanDescription: " + httpReturnMsg + " " + httpReturnStatus);
        System.err.println(stErr);
        sc200 = false;
      } finally {
        if ( stGPD != null ) {
          try {
            stGPD.close();
          } catch (Exception stErr) {
            System.err.println("getPlanDescription: Error closing query statement.");
            System.err.println(stErr);
          }
        }
      }
    } catch (Exception connErr) {
      httpReturnStatus = 500;
      httpReturnMsg = "Error closing database.";
      System.err.println("getPlanDescription: " + httpReturnMsg + " " + httpReturnStatus);
      System.err.println(connErr);
      sc200 = false;
    } finally {
      if ( connGPD != null ) {
        try {
          connGPD.close();
        } catch (Exception connErr) {
          System.err.println("getPlanDescription: Error closing connection.");
          System.err.println(connErr);
        }
      }
    }
    return planDesc.trim();
  }

Answer 1

I have "global" variables defined at the class level

您有在类级别声明的实例变量。 Java 中没有全局变量。

so that I may track the success of a method and determine if I need to send an error response.

技术差

I do this because the method(s) already return a value.

如果返回值已被获取，您应该为此使用异常。

Are those global variables creating an unsafe thread environment

这些实例变量正在创建一个不安全的线程环境。

Since the response is not visible in the private methods, how else might I determine the need to stop the process and send an error response if those global variables are unsafe?

通过方法抛出异常，请参见上文。如果没有异常，则发送 OK 响应，无论采用何种形式，否则发送适合该异常的任何错误响应。

Though clipped for space, should I be doing all of the XML handling in the doGet method

如果它很长或重复(也在其他地方使用)，则不可以。

Should I be calling all of the different private methods for the various data retrieval tasks and data handling

当然，为什么不呢？

Should each method that accesses the same database open a Connection or should the doGet() method create a Connection and pass it to each method

doGet() 应该打开连接，将其传递给每个方法，然后准确地关闭它。

注意，您不需要 ServletConfig 变量，或者 init() 或 getServletConfig() 方法。如果删除所有这些，您可以在需要时通过毫无意义地重写的 getServletConfig() 方法从基类中获取它。