Java：用Lambda表达式简化代码一例

　　之前，调用第3方服务，每个方法都差不多“长”这样, 写起来啰嗦, 改起来麻烦, 还容易改漏。

public void authorizeRoleToUser(Long userId, List<Long> roleIds) {
    try {
        power.authorizeRoleToUser(userId, roleIds);
    } catch (MotanCustomException ex) {
        if (ex.getCode().equals(MSUserException.notLogin().getCode()))
            throw UserException.notLogin();
        if (ex.getCode().equals(MSPowerException.haveNoPower().getCode()))
            throw PowerException.haveNoPower();
        throw ex;
    } catch (MotanServiceException ex) {
        CatHelper.logEventService("Power-authorizeRoleToUser", "authorizeRoleToUser", ex.getStatus(),
                ex.getErrorCode(), ex.getMessage());
        throw ex;
    } catch (MotanAbstractException ex) {
        CatHelper.logEventService("Power-authorizeRoleToUser", "authorizeRoleToUser", ex.getStatus(),
                ex.getErrorCode(), ex.getMessage());
        throw ex;
    } catch (Exception ex) {
        CatHelper.logError(ex);
        throw ex;
    }
}

　　我经过学习和提取封装, 将try ... catch ... catch .. 提取为公用, 得到这2个方法:

import java.util.function.Supplier;

public static <T> T tryCatch(Supplier<T> supplier, String serviceName, String methodName) {
    try {
        return supplier.get();
    } catch (MotanCustomException ex) {
        if (ex.getCode().equals(MSUserException.notLogin().getCode()))
            throw UserException.notLogin();
        if (ex.getCode().equals(MSPowerException.haveNoPower().getCode()))
            throw PowerException.haveNoPower();
        throw ex;
    } catch (MotanServiceException ex) {
        CatHelper.logEventService(serviceName + "-" + methodName, methodName, ex.getStatus(), ex.getErrorCode(),
                ex.getMessage());
        throw ex;
    } catch (MotanAbstractException ex) {
        CatHelper.logEventService(serviceName + "-" + methodName, methodName, ex.getStatus(), ex.getErrorCode(),
                ex.getMessage());
        throw ex;
    } catch (Exception ex) {
        CatHelper.logError(ex);
        throw ex;
    }
}

public static void tryCatch(Runnable runnable, String serviceName, String methodName) {
    tryCatch(() -> {
        runnable.run();
        return null;
    }, serviceName, methodName);
}

　　现在用起来是如此简洁。像这种无返回值的:

public void authorizeRoleToUser(Long userId, List<Long> roleIds) {
    tryCatch(() -> { power.authorizeRoleToUser(userId, roleIds); }, "Power", "authorizeRoleToUser");
}

　　还有这种有返回值的:

public List<RoleDTO> listRoleByUser(Long userId) {
    return tryCatch(() -> power.listRoleByUser(userId), "Power", "listRoleByUser");
}

　　这是我的第一篇Java文章。学习Java的过程中，既有惊喜，也有失望。以后会继续来分享心得。

--------------我是分隔线---------------

后来发现以上2个方法还不够用, 原因是有一些方法会抛出 checked 异常, 于是又再添加了一个能处理异常的, 这次意外发现Java的throws也支持泛型, 赞一个:

public static <T, E extends Throwable> T tryCatchException(SupplierException<T, E> supplier, String serviceName,
        String methodName) throws E {
    try {
        return supplier.get();
    } catch (MotanCustomException ex) {
        if (ex.getCode().equals(MSUserException.notLogin().getCode()))
            throw UserException.notLogin();
        if (ex.getCode().equals(MSPowerException.haveNoPower().getCode()))
            throw PowerException.haveNoPower();
        throw ex;
    } catch (MotanServiceException ex) {
        CatHelper.logEventService(serviceName + "-" + methodName, methodName, ex.getStatus(), ex.getErrorCode(),
                ex.getMessage());
        throw ex;
    } catch (MotanAbstractException ex) {
        CatHelper.logEventService(serviceName + "-" + methodName, methodName, ex.getStatus(), ex.getErrorCode(),
                ex.getMessage());
        throw ex;
    } catch (Exception ex) {
        CatHelper.logError(ex);
        throw ex;
    }
}

@FunctionalInterface
public interface SupplierException<T, E extends Throwable> {

    /**
     * Gets a result.
     *
     * @return a result
     */
    T get() throws E;
}

为了不至于维护两份catch集, 将原来的带返回值的tryCatch改为调用tryCatchException:

public static <T> T tryCatch(Supplier<T> supplier, String serviceName, String methodName) {
    return tryCatchException(() -> supplier.get(), serviceName, methodName);
}

这个世界又完善了一步。

---------------我是第2条分隔线--------------------

前面制作了3种情况:

1.无返回值,无 throws

2.有返回值,无 throws

3.有返回值,有 throws

不确定会不会出现“无返回值，有throws“的情况。后来真的出现了！依样画葫芦，弄出了这个：

public static <E extends Throwable> void tryCatchException(RunnableException<E> runnable, String serviceName,
        String methodName) throws E {
    tryCatchException(() -> {
        runnable.run();
        return null;
    }, serviceName, methodName);
}
@FunctionalInterface
public interface RunnableException<E extends Throwable> {
    void run() throws E;
}

　　现在，”人齐了“，拍张全家福：

 package com.company.system.util;

 import java.util.function.Supplier;

 import org.springframework.beans.factory.BeanCreationException;

 import com.company.cat.monitor.CatHelper;
 import com.company.system.customException.PowerException;
 import com.company.system.customException.ServiceException;
 import com.company.system.customException.UserException;
 import com.company.hyhis.ms.user.custom.exception.MSPowerException;
 import com.company.hyhis.ms.user.custom.exception.MSUserException;
 import com.company.hyhis.ms.user.custom.exception.MotanCustomException;
 import com.weibo.api.motan.exception.MotanAbstractException;
 import com.weibo.api.motan.exception.MotanServiceException;

 public class ThirdParty {

     public static void tryCatch(Runnable runnable, String serviceName, String methodName) {
         tryCatch(() -> {
             runnable.run();
             return null;
         }, serviceName, methodName);
     }

     public static <T> T tryCatch(Supplier<T> supplier, String serviceName, String methodName) {
         return tryCatchException(() -> supplier.get(), serviceName, methodName);
     }

     public static <E extends Throwable> void tryCatchException(RunnableException<E> runnable, String serviceName,
             String methodName) throws E {
         tryCatchException(() -> {
             runnable.run();
             return null;
         }, serviceName, methodName);
     }

     public static <T, E extends Throwable> T tryCatchException(SupplierException<T, E> supplier, String serviceName,
             String methodName) throws E {
         try {
             return supplier.get();
         } catch (MotanCustomException ex) {
             if (ex.getCode().equals(MSUserException.notLogin().getCode()))
                 throw UserException.notLogin();
             if (ex.getCode().equals(MSPowerException.haveNoPower().getCode()))
                 throw PowerException.haveNoPower();
             throw ex;
         } catch (MotanServiceException ex) {
             CatHelper.logEventService(serviceName + "-" + methodName, methodName, ex.getStatus(), ex.getErrorCode(),
                     ex.getMessage());
             throw ex;
         } catch (MotanAbstractException ex) {
             CatHelper.logEventService(serviceName + "-" + methodName, methodName, ex.getStatus(), ex.getErrorCode(),
                     ex.getMessage());
             throw ex;
         } catch (Exception ex) {
             CatHelper.logError(ex);
             throw ex;
         }
     }

     @FunctionalInterface
     public interface RunnableException<E extends Throwable> {
         void run() throws E;
     }

     @FunctionalInterface
     public interface SupplierException<T, E extends Throwable> {
         T get() throws E;
     }
 }