Java 中的分页

Pagination in Java

提问by user569125

I wrote paging logic:

我写了分页逻辑：

My requirement: total elements to display:100 per page,if i click next it should display next 100 records,if i click previous 100 records.

我的要求：要显示的总元素：每页 100 个，如果我点击下一步，它应该显示接下来的 100 条记录，如果我点击前 100 条记录。

Initial varaible values:

初始变量值：

• showFrom:1,
• showTo:100
• max elements:depends on size of data.
• pageSize:100.

• 显示来自:1,
• 显示到：100
• 最大元素：取决于数据的大小。
• 页面大小：100。

Code:

代码：

if(paging.getAction().equalsIgnoreCase("Next")){
  paging.setTotalRec(availableList.size());
  showFrom = (showTo + 1);
  showTo = showFrom + 100- 1;
  if(showTo >= paging.getTotalRec())
    showTo = paging.getTotalRec();
  paging.setShowFrom(showFrom);
  paging.setShowTo(showTo);
}

else if(paging.getAction().equalsIgnoreCase("Previous")){
  showTo = showFrom - 1;
  showFrom = (showFrom - 100);
  paging.setShowTo(showTo);
  paging.setShowFrom(showFrom);
  paging.setTotalRec(availableList.size());
}

Here i can remove and add the elements to the existing data.above code works fine if i add and remove few elements.but if i remove or add 100 elements at a time counts are not displaying properly above code works fine if i add and remove few elements.

在这里，我可以删除元素并将其添加到现有数据中。如果我添加和删除几个元素，上面的代码工作正常。但是如果我一次删除或添加 100 个元素，则计数显示不正确，如果我添加和删除，上面的代码工作正常几个元素。

采纳答案by brian_d

Some things to improve:

一些需要改进的地方：

• replace "magic" value of 100 with final int PAGE_SIZE = 100;
• factor out redundant code.

• 用 100 替换“magic”值 final int PAGE_SIZE = 100;
• 剔除冗余代码。

  paging.setShowTo(showTo);
  paging.setShowFrom(showFrom);
  paging.setTotalRec(availableList.size());

  paging.setShowTo(showTo);
  paging.setShowFrom(showFrom);
  paging.setTotalRec(availableList.size());

to outside of if/else to make your logic clearer

到 if/else 之外，让你的逻辑更清晰

• Ensure that previous >= 0 and next <= number of records

• 确保前一个 >= 0 和下一个 <= 记录数

Edit:

编辑：

final int PAGE_SIZE = 100;
int numberOfPages = -1;
int currentPage = -1;

public void initializeVariables(){
  paging.setTotalRec(availableList.size());
  showFrom = 1; 
  showTo = PAGE_SIZE;
  //keep track of how many pages there should be
  numberOfPages = paging.getTotalRec()/PAGE_SIZE;
  currentPage = 1;
}

public void handlePagingAction(){
  if(paging.getAction().equalsIgnoreCase("Next")){
     if(currentPage < numberOfPages){
        ++currentPage;
     }
  }else if(paging.getAction().equalsIgnoreCase("Previous")){
     if(currentPage > 1){       
       --currentPage;
     }
  }      

  showFrom = (currentPage - 1) * PAGE_SIZE + 1;
  if(showFrom < 0){
    showFrom = 0
  }

  showTo = currentPage * PAGE_SIZE;
  if(showTo >= paging.getTotalRec()){
    showTo = paging.getTotalRec();
  }     

  paging.setShowTo(showTo);
  paging.setShowFrom(showFrom);
}

回答by Alexis Dufrenoy

Some remarks:

一些备注：

• In the line showTo = showFrom + 100- 1;, why minus 1?
• If showTo is equal to paging.getTotalRec(), the next time you press Next, showFrom will be over paging.getTotalRec()
• In the Previous part, tests to prevent going below 0 are missing

• 在行中showTo = showFrom + 100- 1;，为什么是负 1？
• 如果 showTo 等于 paging.getTotalRec()，则下次您按 Next 时，showFrom 将超过 paging.getTotalRec()
• 在上一部分中，缺少防止低于 0 的测试

Hope this helps...

希望这可以帮助...