com.feilong.taglib.display.pager.PagerBuilder Maven / Gradle / Ivy

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feilong is a suite of core and expanded libraries that include utility classes, http, excel,cvs, io classes, and much much more.
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/*
 * Copyright (C) 2008 feilong
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *         http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.feilong.taglib.display.pager;

import static com.feilong.core.lang.StringUtil.EMPTY;

import java.util.List;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.feilong.json.JsonUtil;
import com.feilong.lib.lang3.StringUtils;
import com.feilong.core.Validate;
import com.feilong.taglib.display.SimpleTagParamCacheManager;
import com.feilong.taglib.display.pager.command.Pager;
import com.feilong.taglib.display.pager.command.PagerAndContent;
import com.feilong.taglib.display.pager.command.PagerConstants;
import com.feilong.taglib.display.pager.command.PagerParams;
import com.feilong.taglib.display.pager.command.PagerUrlTemplate;
import com.feilong.taglib.display.pager.command.PagerVMParam;

/**
 * 分页构造器.
 * 
 * 
 * 该类主要是将url相关数据转成vm需要的数据,并解析成字符串返回.
 * 
 * 
 * 日志:
 * 
 * 
 * 
 * 内部会分别对入参 {@link PagerParams} 和构造vm参数,记录 debug 级别的log,

 * 如果不需要care这部分log,可以在日志配置文件中配置,将log输出的级别调高
 * 
 * 
 * log4j.xml
 * 
 *  * {@code
 *  
 *      
 *  
 * }
 * 
 * 
 * logback.xml
 * 
 *  * {@code
 *      
 * }
 * 
 * 
 * 
 * 
 * VM中支持国际化:
 * 
 * 
 * 
 * VM中支持国际化,您可以见国际化需要的参数 设置到 {@link PagerConstants#I18N_FEILONG_PAGER} 配置文件中, 

 * 程序会解析该文件所有的key/values到 {@link PagerConstants#VM_KEY_I18NMAP} 变量,您可以在VM中直接使用
 * 
 * 
 * 
 * 缓存:
 * 
 * 
 * 
 * 作为vm解析,如果是官方商城常用页面渲染,在大流量的场景下,其实开销也是不小的,

 * 基于如果传入的参数 {@link PagerParams}是一样的 {@link PagerParams#hashCode()} &&{@link PagerParams#equals(Object)},那么分页结果也应该是相同的

 * 因此,如果对性能有很高的要求的话,可以使用cache
 * 
 * 
 * 缓存清理:
 * 
 * 
 * 
 * 当vm模板内容更改,需要清理缓存,由于pagerCache 是基于JVM内存级的,因此重启应用即会生效
 * 
 * 
 * 
 * 
 * 
 * @author feilong
 * @see PagerConstants
 * @see PagerParams
 * @see PagerUrlTemplate
 * @see PagerVMParam
 * @since 1.0.0
 */
public final class PagerBuilder{

    /** The Constant LOGGER. */
    private static final Logger LOGGER = LoggerFactory.getLogger(PagerBuilder.class);

    /** Don't let anyone instantiate this class. */
    private PagerBuilder(){
        //AssertionError不是必须的. 但它可以避免不小心在类的内部调用构造器. 保证该类在任何情况下都不会被实例化.
        //see 《Effective Java》 2nd
        throw new AssertionError("No " + getClass().getName() + " instances for you!");
    }

    //---------------------------------------------------------------

    /**
     * 通常用于ajax分页.
     *
     * @param 
     *            the generic type
     * @param pagerParams
     *            the pager params
     * @param itemList
     *            the item list
     * @return the pager and content
     * @see com.feilong.taglib.display.pager.command.PagerType#NO_REDIRECT
     * @since 1.4.0
     */
    public static  PagerAndContent buildPagerAndContent(PagerParams pagerParams,List itemList){
        Pager pager = PagerCacheContentBuilder.buildPager(pagerParams);
        pager.setItemList(itemList);

        return new PagerAndContent<>(pager, buildContent(pagerParams));
    }

    //---------------------------------------------------------------

    /**
     * 解析VM模板,生成分页HTML代码.
     * 
     * maybe you want to return {@link PagerAndContent}
     * 
     * 
     * 
     * 你可以拿到结果,再次封装成 {@link PagerAndContent}
     * 
     * 
     * 
     * @param pagerParams
     *            构造分页需要的请求参数
     * @return 如果 pagerParams 是null,抛出 {@link NullPointerException}

     *         如果 {@link PagerParams#getTotalCount()}{@code <=0} 返回 {@link StringUtils#EMPTY} 

     *         否则 生成分页html代码
     */
    public static String buildContent(PagerParams pagerParams){
        Validate.notNull(pagerParams, "pagerParams can't be null!");

        if (pagerParams.getTotalCount() <= 0){
            LOGGER.debug("totalCount value is [{}] not > 0,will return empty", pagerParams.getTotalCount());
            return EMPTY;// 如果总数不>0 则直接返回 empty,页面分页地方显示空白
        }

        //---------------------------------------------------------------
        if (LOGGER.isTraceEnabled()){
            LOGGER.trace("input [pagerParams] info:{}", JsonUtil.format(pagerParams));
        }

        return SimpleTagParamCacheManager.getContent(pagerParams, PagerCacheContentBuilder.INSTANCE);
    }
}