Question

我是Lambda的新手，我想将具有很多if-else的简单代码转换为Lambda代码。谁能解释我该怎么做？我不太了解如何构建它

public void registerModule(HttpServletRequest req, ModuleType moduleType) {
    LOGGER.debug("Register New Module - " + moduleType.name());
    ModuleEntityGenerator moduleEntityGenerator = new ModuleEntityGenerator();
    try {
        if (!req.getParts().isEmpty() && !req.getParameterMap().isEmpty()) {
            ModuleEntityDao moduleEntityDao = moduleEntityGenerator.get(req, moduleType);
            if (moduleEntityDao != null) {
                if (processRegistryDal.getModule(moduleType, moduleEntityDao.getId()) == null) { // Check BA is not already exist
                    processRegistryDal.addNewModule(moduleEntityDao);
                } else { // If already exists just update the current row
                    processRegistryDal.updateModule(moduleEntityDao);
                }
            } else {
                LOGGER.error("The BA object is null. There is nothing to register");
            }
        } else {
            LOGGER.error("The rest request is empty.No info to register");
        }
    } catch (IOException e) {
        LOGGER.error("IO Error\n" + e.getMessage());
    } catch (ServletException e) {
        LOGGER.error("Servlet Error\n" + e.getMessage());
    }
}

Answer 1

这里与lambda无关，只是一个快速的清理提示。早期的return是一种扁平化代码的好方法，可以使代码的表观复杂度更接近其实际复杂度。只需反转您的if条件的含义，拉出错误日志，然后返回即可。看看这一转换可以使您的代码更好。

public void registerModule(HttpServletRequest req, ModuleType moduleType) {
    LOGGER.debug("Register New Module - " + moduleType.name());
    try {
        if (req.getParts().isEmpty() || req.getParameterMap().isEmpty()) {
            LOGGER.error("The rest request is empty.No info to register");
            return;
        }

        ModuleEntityGenerator moduleEntityGenerator = new ModuleEntityGenerator();
        ModuleEntityDao moduleEntityDao = moduleEntityGenerator.get(req, moduleType);
        if (moduleEntityDao == null) {
          LOGGER.error("The BA object is null. There is nothing to register");
          return;
        }

        if (processRegistryDal.getModule(moduleType, moduleEntityDao.getId()) == null) { // Check BA is not already exist
            processRegistryDal.addNewModule(moduleEntityDao);
        } else { // If already exists just update the current row
            processRegistryDal.updateModule(moduleEntityDao);
        }
    } catch (IOException e) {
        LOGGER.error("IO Error\n" + e.getMessage());
    } catch (ServletException e) {
        LOGGER.error("Servlet Error\n" + e.getMessage());
    }
}

Answer 2

如果只是简单地重新组织代码，就不会得到太多嵌套的if语句。

例如逆转条件。代替：

if (a) {
    if (b) {
        // code here
    } else {
        // ERROR
    }
} else {
    // ERROR
}

将其转过来并使用else-if构造：

if (! a) {
    // ERROR
} else if (! b) {
    // ERROR
} else {
    // code here
}

一个附带的好处是，短的“ ERROR”逻辑在if条件旁边处理，而不是出现在更远的地方，因为条件和操作分开得太远了。

使用您的代码，可以像这样简化：

public void registerModule(HttpServletRequest req, ModuleType moduleType) {
    LOGGER.debug("Register New Module - " + moduleType.name());
    try {
        ModuleEntityDao moduleEntityDao;
        if (req.getParts().isEmpty() || req.getParameterMap().isEmpty()) {
            LOGGER.error("The rest request is empty.No info to register");
        } else if ((moduleEntityDao = new ModuleEntityGenerator().get(req, moduleType)) == null) {
            LOGGER.error("The BA object is null. There is nothing to register");
        } else if (processRegistryDal.getModule(moduleType, moduleEntityDao.getId()) == null) { // Check BA is not already exist
            processRegistryDal.addNewModule(moduleEntityDao);
        } else { // If already exists just update the current row
            processRegistryDal.updateModule(moduleEntityDao);
        }
    } catch (IOException e) {
        LOGGER.error("IO Error\n" + e.getMessage());
    } catch (ServletException e) {
        LOGGER.error("Servlet Error\n" + e.getMessage());
    }
}

Answer 3

如何将每个if分成范围较小的单独方法。

主要方法看起来很简单。

public void registerModule(HttpServletRequest req, ModuleType moduleType) {
    LOGGER.debug("Register New Module - " + moduleType.name());

    try {
        if (!isRequestEmpty(req))
            addOrUpdateModule(createModule(req, moduleType));
    } catch (IOException e) {
        LOGGER.error("IO Error\n" + e.getMessage());
    } catch (ServletException e) {
        LOGGER.error("Servlet Error\n" + e.getMessage());
    }
}

Helper方法。如果开发人员需要详细信息，请查看它。

private static boolean isRequestEmpty(HttpServletRequest req) {
    if (req.getParts().isEmpty() || req.getParameterMap().isEmpty()) {
        LOGGER.error("The rest request is empty.No info to register");
        return true;
    }

    return false;
}

private static ModuleEntityDao createModule(HttpServletRequest req, ModuleType moduleType) {
    ModuleEntityDao module = new ModuleEntityGenerator().get(req, moduleType);

    if (module != null)
        return module;

    LOGGER.error("The BA object is null. There is nothing to register");
    return module;
}

private void addOrUpdateModule(ModuleEntityDao module) {
    if(module == null)
        return;

    if(processRegistryDal.getModule(module.getModuleType(), module.getId()) == null)
        processRegistryDal.addNewModule(moduleEntityDao);
    else
        processRegistryDal.updateModule(moduleEntityDao);
}

Answer 4

这不是lamda，但是可以通过调用“ return”在输入无效的情况下立即退出函数，从而使程序易于读取。

if (a != null && b != null) {
   // c
}
else {
   // d
}

到

if (a == null || b == null) {
   // d
   return;
}

// c

示例

public void registerModule(HttpServletRequest req, ModuleType moduleType) {
    try {
        LOGGER.debug("Register New Module - " + moduleType.name());
        ModuleEntityGenerator moduleEntityGenerator = new ModuleEntityGenerator();

        if (req.getParts().isEmpty() || req.getParameterMap().isEmpty()) {
            LOGGER.error("The rest request is empty.No info to register");
            return;
        }

        ModuleEntityDao moduleEntityDao = moduleEntityGenerator.get(req, moduleType);
        if (moduleEntityDao == null) {
            LOGGER.error("The BA object is null. There is nothing to register");
            return;
        }     

        if (processRegistryDal.getModule(moduleType, moduleEntityDao.getId()) == null) { 
            // Check BA is not already exist
            processRegistryDal.addNewModule(moduleEntityDao);
            return;
        }

        // If already exists just update the current row
        processRegistryDal.updateModule(moduleEntityDao);

    } catch (Exception ex) {
        LOGGER.error("Error\n" + ex.getMessage());
    }
}

在Java中将多if-else转换为简单的Lambda表达式代码

4 个答案: