SpringBoot MP简单的分页查询测试实现步骤分解

        <dependency>
            <groupId>com.baomidou</groupId>
            <artifactId>mybatis-plus-boot-starter</artifactId>
            <version>3.5.2</version>
        </dependency>

public class MybatisPlusInterceptor implements Interceptor {
    private List<InnerInterceptor> interceptors = new ArrayList();
    public MybatisPlusInterceptor() {}
    public Object intercept(Invocation invocation) throws Throwable {}
    public Object plugin(Object target) {}
    public void addInnerInterceptor(InnerInterceptor innerInterceptor) {}
    public List<InnerInterceptor> getInterceptors() {}
    public void setProperties(Properties properties) {}
    public void setInterceptors(final List<InnerInterceptor> interceptors) {}
}

public interface InnerInterceptor {
    default boolean willDoQuery(Executor executor, MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, Boundsql boundSql) throws SQLException {
        return true;
    }
    default void beforeQuery(Executor executor, MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) throws SQLException {
    }
    default boolean willDoUpdate(Executor executor, MappedStatement ms, Object parameter) throws SQLException {
        return true;
    }
    default void beforeUpdate(Executor executor, MappedStatement ms, Object parameter) throws SQLException {
    }
    default void beforePrepare(StatementHandler sh, Connection connection, Integer transactionTimeout) {
    }
    default void beforeGetBoundSql(StatementHandler sh) {
    }
    default void setProperties(Properties properties) {
    }
}

public class PaginationInnerInterceptor implements InnerInterceptor {
    protected static final List<SelectItem> COUNT_SELECT_ITEM = Collections.singletonList((new SelectExpressionItem((new Column()).withColumnName("COUNT(*)"))).withAlias(new Alias("total")));
    protected static final Map<String, MappedStatement> countMsCache = new ConcurrentHashMap();
    protected final Log logger = LogFactory.getLog(this.getClass());
    protected boolean overflow;
    protected Long maxLimit;
    private DbType dbType;
    private IDialect dialect;
    protected boolean optimizeJoin = true;
    public PaginationInnerInterceptor(DbType dbType) {
        this.dbType = dbType;
    }
    public PaginationInnerInterceptor(IDialect dialect) {
        this.dialect = dialect;
    }
    public boolean willDoQuery(Executor executor, MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) throws SQLException {
        IPage<?> page = (IPage)ParameterUtils.findPage(parameter).orElse((Object)null);
        if (page != null && page.getSize() >= 0L && page.searchCount()) {
            MappedStatement countMs = this.buildCountMappedStatement(ms, page.countId());
            BoundSql countSql;
            if (countMs != null) {
                countSql = countMs.getBoundSql(parameter);
            } else {
                countMs = this.buildAutoCountMappedStatement(ms);
                String countSqlStr = this.autoCountSql(page, boundSql.getSql());
                MPBoundSql mpBoundSql = PluginUtils.mpBoundSql(boundSql);
                countSql = new BoundSql(countMs.getConfiguration(), countSqlStr, mpBoundSql.parameterMappings(), parameter);
                PluginUtils.setAdditionalParameter(countSql, mpBoundSql.additionalParameters());
            }
            CacheKey cacheKey = executor.createCacheKey(countMs, parameter, rowBounds, countSql);
            List<Object> result = executor.query(countMs, parameter, rowBounds, resultHandler, cacheKey, countSql);
            long total = 0L;
            if (CollectionUtils.isNotEmpty(result)) {
                Object o = result.get(0);
                if (o != null) {
                    total = Long.parseLong(o.toString());
                }
            }
            page.setTotal(total);
            return this.continuePage(page);
        } else {
            return true;
        }
    }
    public void beforeQuery(Executor executor, MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) throws SQLException {...........省略之后全部的内容........}

import com.baomidou.mybatisplus.annotation.DbType;
import com.baomidou.mybatisplus.extension.plugins.MybatisPlusInterceptor;
import com.baomidou.mybatisplus.extension.plugins.inner.PaginationInnerInterceptor;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
@Configuration
public class MpConfig {
    
    @Bean
    public MybatisPlusInterceptor mybatisPlusInterceptor() {
        
        MybatisPlusInterceptor interceptor = new MybatisPlusInterceptor();
        
        PaginationInnerInterceptor pagInterceptor = new PaginationInnerInterceptor();
        
        pagInterceptor.setOverflow(false);
        
        pagInterceptor.setMaxLimit(500L);
        
        pagInterceptor.setDbType(DbType.Mysql);
        
        interceptor.addInnerInterceptor(pagInterceptor);
        return interceptor;
    }
}

import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.hlc.mp.entity.Product;
import org.apache.ibatis.annotations.Mapper;
@Mapper
public interface ProductMapper extends BaseMapper<Product> {
}

import com.baomidou.mybatisplus.core.conditions.query.QueryWrapper;
import com.baomidou.mybatisplus.extension.plugins.pagination.Page;
import com.baomidou.mybatisplus.extension.service.IService;
import com.baomidou.mybatisplus.extension.service.impl.ServiceImpl;
import com.hlc.mp.entity.Product;
import com.hlc.mp.mapper.ProductMapper;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import java.util.List;
@Service(value = "ProductService")
public class ProductServiceImpl extends ServiceImpl<ProductMapper, Product>
        implements IService<Product> {
    @Autowired
    ProductMapper productMapper;
    
    public Page<Product> page(Long current) {
        
        Page<Product> productPage = new Page<>(current, 1);
        
        QueryWrapper<Product> queryWrapper = new QueryWrapper<>();
        queryWrapper.eq("status", 0);
        productMapper.selectPage(productPage, queryWrapper);
        return productPage;
    }
}

    @Test
    public void testPage(){
        IPage<Product> productIPage = productService.page(2L);
        productIPage.getRecords().forEach(System.out::println);
        System.out.println("当前页码"+productIPage.getCurrent());
        System.out.println("每页显示数量"+productIPage.getSize());
        System.out.println("总页数"+productIPage.getPages());
        System.out.println("数据总量"+productIPage.getTotal());
    }