Springboot下PageHelper的封装

先说思路，使用pagehelper分页十分方便，本文只做简单的封装，通过反射机制获取service的查询方法并执行，提升分页查询调用方便程度。

1. 在springboot项目中引入pagehelper的pom依赖：

        <dependency>
            <groupId>com.github.pagehelper</groupId>
            <artifactId>pagehelper-spring-boot-starter</artifactId>
            <version>1.2.10</version>
        </dependency>

2. 编写SpringUtil类，用于从Spring中获取Bean，用于后续的反射获取的方法的执行：

import org.springframework.beans.BeansException;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;

public class SpringUtils implements ApplicationContextAware {

    private static ApplicationContext applicationContext;


    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        if(SpringUtils.applicationContext == null) {
            SpringUtils.applicationContext = applicationContext;
        }
    }

    private static ApplicationContext getApplicationContext() {
        return applicationContext;
    }

    public static <T> T getBean(Class<T> clazz){
        return getApplicationContext().getBean(clazz);
    }
}

3. 在springboot的入口处，初始化ApplicationContext，为SpringUtil获取ApplicationContext：

    public static void main(String[] args) {
        ApplicationContext applicationContext = SpringApplication.run(FoundationApplication.class, args);
        new SpringUtils().setApplicationContext(applicationContext);
    }

4. 封装分页类，核心思想为：先获取要执行查询的service，查询方法名，参数类型列表，再通过反射执行查询，PageHelper会自动将查询结果分页。AbstractService为所有使用分页查询的Service的父类

import com.github.pagehelper.PageInfo;
import com.github.pagehelper.page.PageMethod;
import org.cicada.chtp.foundation.common.utils.SpringUtils;
import org.cicada.chtp.foundation.service.AbstractService;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.ArrayList;

public class PageSelector<T> {

    private AbstractService service;
    private String selectMethodName;
    private Class<?>[] paramTypes;
    private static final Logger  logger = LoggerFactory.getLogger("记录查询分页器（page helper）");


    private PageSelector(AbstractService service, String selectMethodName, Class<?>[] paramTypes){
        this.service = service;
        this.selectMethodName = selectMethodName;
        this.paramTypes = paramTypes;
    }

    public static<T> PageSelector<T> build(AbstractService service, String selectMethodName, Class<?>...paramTypes){
        return new PageSelector<>(service, selectMethodName, paramTypes);
    }


    public PageInfo<T> selectByPage(int pageNum, int pageSize, Object...args) throws Throwable {
        Method selectMethod = getSelectMethod();
        PageInfo<T> pageInfo = null;
        AbstractService instance;
        instance = SpringUtils.getBean(service.getClass());
        try {
            PageMethod.startPage(pageNum, pageSize);
            ArrayList<T> list = (ArrayList<T>)selectMethod.invoke(instance, args);
            pageInfo = new PageInfo<>(list);
        }
        catch (IllegalAccessException ie){
            logger.error(ie.getLocalizedMessage());
        }
        catch (InvocationTargetException e) {
            Throwable t = e.getTargetException();
            String selectMethodName = selectMethod.getName();
            String errorMsg = "分页查询时发生错误，方法名: " + selectMethodName + "\n";
            logger.error(errorMsg + t.getLocalizedMessage());
            throw t;
        }
        return pageInfo;
    }

    private Method getSelectMethod(){
        Method method = null;
        try {
            method = service.getClass().getDeclaredMethod(selectMethodName, paramTypes);
        } catch (NoSuchMethodException e) {
            e.printStackTrace();
        }
        return method;
    }
}

5. controller里使用分页查询，如Service的查询需要参数，在build中传入参数类型的.class，在selectByPage中传入实际参数:

PageSelector<User> pageSelector = PageSelector.build(userService, "getUserList");
        try {
            response.setData(pageSelector.selectByPage(pageNum, pageSize));
        } catch (Throwable throwable) {
            response.setServiceCode(Code.FAIL);
            response.setMsg(throwable.getLocalizedMessage());
        }