springmvc+jpa实现分页的两种方式

1.工具类

public final class QueryTool {
    public static PageRequest buildPageRequest(int pageNumber, int pageSize, String sortType){
        Sort sort = null;
        if("auto".equals(sortType)) {
            sort = new Sort(Direction.DESC, "ctime");
        } else {
            sort = new Sort(Direction.DESC, "ctime");
        }

        return new PageRequest(pageNumber, pageSize, sort);
    }

    public static <T> Specification<T> buildSpecification(Map<String, Object> searchParams, Class<T> domainClass){
        Map<String, SearchFilter> filters = SearchFilter.parse(searchParams);
        Specification<T> spec = DynamicSpecifications.bySearchFilter(filters.values(), domainClass);
        return spec;
    }
}

2.Service类（只给出CommentService）

@Service
public class CommentService {
    @Autowired
    private CommentDao commentDao;

    @Transactional
    public void addComment(Comment comment) {
        if(comment == null) return;
        commentDao.save(comment);
    }

    @Transactional
    public Page<Comment> findAllComments(String problemId, PageRequest pageable){
        Page<Comment> page = commentDao.findAllCommentsByProblemId(problemId, pageable);
        return page;
    }
}

3.repository类（problem 和 comment 属于 一对多 的关系）

@Repository
public interface CommentDao extends JpaSpecificationExecutor<Comment>,
    PagingAndSortingRepository<Comment, String> {

    @Query("select c from Comment c where c.problem.problemid = ?1")
    public Page<Comment> findAllCommentsByProblemId(String problemId, Pageable pageable);
}

4.Controller类

　　第一种方式

@Controller
public class ProblemController {

    @Autowired
    private ProblemService problemService;

    @Autowired
    private CommentService commentService;

    @RequestMapping(value="getCurProblemComments")
    @ResponseBody
    public String getCurProblemComments(String problemName, @RequestParam(value = "pn", defaultValue = "1") int pageNumber,
            @RequestParam(value = "ps", defaultValue = "4") int pageSize,
            @RequestParam(value = "sortType", defaultValue = "auto") String sortType){
        JSONObject jsono = new JSONObject();
        try {
            Problem problem = problemService.getProblemByName(problemName);
            if(problem == null){
                problem = problemService.addProblem(problemName);
            }
            PageRequest pageRequest = QueryTool.buildPageRequest(pageNumber, pageSize, sortType);
            //根据题目的id获取所有的评论
            Page<Comment> page = commentService.findAllComments(problem.getProblemid(), pageRequest);
            //对 Comment 这个类中的一些字段进行过滤
            SimplePropertyPreFilter spp = new SimplePropertyPreFilter();
            spp.getExcludes().addAll(Comment.getExcludeString());
            jsono.put("success", true);
            jsono.put("message", JSON.toJSONString(page, spp));
        } catch(Exception e){
            e.printStackTrace();
            jsono.put("success", false);
            jsono.put("message", "inner error.");
        }
        return jsono.toString();
    }
}

　　

　　第二种方式，（懒了，有些内容是放在servic中的。）

　　通过JpaSpecificationExecutor<T> 的Page<T> findAll(Specification<T> spec, Pageable pageable); 方法（按照指定的规格条件）实现分页查询。

public String getCurProblemComments(@RequestParam(value = "pn", defaultValue = "1") int pageNumber,
        @RequestParam(value = "ps", defaultValue = "2") int pageSize,
        @RequestParam(value = "sortType", defaultValue = "auto") String sortType, ServletRequest request) {
    Map<String, Object> searchParams = new HashMap<String, Object>();
    searchParams = Servlets.getParametersStartingWith(request, "search_");
    System.out.println(EncodeUtils.toUTF8((String)searchParams.get("LIKE_name")));
    PageRequest pageRequest = QueryTool.buildPageRequest(pageNumber, pageSize, sortType);
    searchParams.put(Operator.EQ + "_dr", "0");//逻辑删除中，字段dr=0表示这条数据没有删除
    Specification<Comment> spec = QueryTool.buildSpecification(searchParams, Comment.class);
    Page<Comment> page = commentDao.findAll(spec, pageRequest);
    return JSON.toJSONString(page);
}

　　其中，Specification中的一些比较操作org.springside.modules.persistence.SearchFilter.Operator这个类中找到，如下：

public static enum Operator {
   EQ, LIKE, GT, LT, GTE, LTE;
}

　　前台传递过来的参数名称中可以包含 Operator 中的一些操作， 比如参数名称是： search_LIKE_name (search表示要查询时比较， LIKE是比较的操作， name是表的字段名)。

5.java简单实现分页

分页面板类（MyPagePanel.java）

public class MyPagePanel extends JPanel{
    private final int PAGE_BTN_NUM = 6;//按钮的数目的最大值, 一定为偶数
    private JButton[] pageBtns = new JButton[PAGE_BTN_NUM];
    private JButton preBtn = new JButton("<<");//前一页
    private JButton nextBtn = new JButton(">>");//后一页

    private JButton jumpBtn = new JButton("跳转");
    private JTextField jumpText = new JTextField(5);//输入页号
    private JLabel totPageLabel = new JLabel("共0页");//提示一共多少页

    public static final int PAGE_SIZE = 2;
    private CommunicationPanel parentPanel;
    private ChatPanel chatPanel;
    //刷新某页
    public void refreshPage(){
        if(curPage == -1){
            JOptionPane.showMessageDialog(null, "请选择题目，然后再刷新!", "温馨提示",JOptionPane.WARNING_MESSAGE);
        } else {
            requestPage(curPage);
        }
    }
    //请求某页
    public void requestPage(int pageNumber){
        //当前页按钮设为 true
        if(curBtnPos >= 0)
            pageBtns[curBtnPos].setEnabled(true);

        JSONObject jsono = new JSONObject();
        jsono.put("problemName", JavaRequest.problemName);
        jsono.put("pageSize", String.valueOf(PAGE_SIZE));
        jsono.put("pageNumber", String.valueOf(pageNumber));
        String data = JavaRequest.sendPost("getCurProblemComments", jsono);

        //获取当前题目的 评论记录
        JSONObject result = JSONObject.fromObject(data);
        if((Boolean) result.get("success")){//分页显示
            JSONObject message = JSONObject.fromObject(result.get("message"));
            Map<String, Class<?>> classMap = new HashMap<String, Class<?>>();
            classMap.put("content", MyMessage.class);
            MyPage myPage = (MyPage) JSONObject.toBean(message, MyPage.class, classMap);
            this.updatePage(myPage);
        } else {
            JOptionPane.showMessageDialog(null, result.getString("message"), "温馨提示",JOptionPane.WARNING_MESSAGE);
            if(result.get("returnLogin") != null && (Boolean)result.get("returnLogin")){//如果用户登录超时返回用户登陆界面
                parentPanel.switchPanel(CommunicationPanel.LOGIN_PANEL);
            }
        }
    }
    //跳转都页面
    private void jumpPage(int pageNumber) throws Exception{
        if(pageNumber < 0 || pageNumber >= totalPages)
            throw new Exception("不存在该页号!");
        requestPage(pageNumber);
    }

    public MyPagePanel(CommunicationPanel parentPanelx, ChatPanel chatPanelx){
        this.parentPanel = parentPanelx;
        this.chatPanel = chatPanelx;

        preBtn.setEnabled(false);
        this.add(preBtn);
        preBtn.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                requestPage(curPage-1);
            }
        });

        for(int i=0; i<pageBtns.length; ++i) {
            pageBtns[i] = new JButton();
            this.add(pageBtns[i]);
            pageBtns[i].setVisible(false);
            pageBtns[i].addActionListener(new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    //JButton text 表示的是页号
                    String text = ((JButton)e.getSource()).getText();
                    int pageNumber = Integer.valueOf(text);
                    requestPage(pageNumber);
                }
            });
        }

        nextBtn.setEnabled(false);
        this.add(nextBtn);
        nextBtn.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                requestPage(curPage+1);
            }
        });

        jumpBtn.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                try{
                    if(jumpText.getText().isEmpty()) throw new Exception("页数不能为空!");
                    int pageNumber = Integer.valueOf(jumpText.getText());
                    jumpPage(pageNumber);
                } catch (Exception ex){
                    ex.printStackTrace();
                    JOptionPane.showMessageDialog(null, "请确定页号是否正确!", "温馨提示",JOptionPane.WARNING_MESSAGE);
                }
            }
        });
        this.add(totPageLabel);
        this.add(jumpText);
        this.add(jumpBtn);
    }
    private int curPage = -1, totalPages, curBtnPos = -1;
    public void updatePage(MyPage myPage){
        //清除当页面的信息
        chatPanel.getJpChat().setText("");
        //处理接受到的 评论消息
        for(MyMessage message : myPage.getContent()){
            chatPanel.addRecMsg(message.getCcontent(), StyleConstants.ALIGN_LEFT);
        }

        curPage = myPage.getNumber();
        totalPages = myPage.getTotalPages();
        totPageLabel.setText("共" + totalPages + "页");

        if(curPage == 0) preBtn.setEnabled(false);
        else preBtn.setEnabled(true);

        if(curPage == totalPages-1 || totalPages == 0) nextBtn.setEnabled(false);
        else nextBtn.setEnabled(true);

        List<Integer> pageNum = new LinkedList<Integer>();
        if(totalPages > 0) {
            int step = PAGE_BTN_NUM/2-1;
            for(int i=step; i>=1; --i) {
                if(curPage-i>=0)
                    pageNum.add(curPage-i);
            }

            pageNum.add(curPage);

            for(int i=1; i<=step+1 && curPage+i<totalPages; ++i)
                pageNum.add(curPage+i);

            if(pageNum.size() < PAGE_BTN_NUM){
                while(pageNum.size() < PAGE_BTN_NUM && pageNum.get(0)-1 >= 0)
                    pageNum.add(0, pageNum.get(0)-1);

                while(pageNum.size() < PAGE_BTN_NUM && pageNum.get(pageNum.size()-1)+1 < totalPages)
                    pageNum.add(pageNum.get(pageNum.size()-1)+1);
            }
        }

        int bi = 0;
        for(int pi=0; pi < pageNum.size(); ++pi, ++bi){
            pageBtns[bi].setText(String.valueOf(pageNum.get(pi)));
            if(pageNum.get(pi) == curPage){
                curBtnPos = bi;//记录这个按钮的页号值 和 当前页号值相等
            }
        }
        //重新显示按钮
        for(int i=0; i<bi; ++i)
            pageBtns[i].setVisible(true);

        //后面这些按钮都是没有 用上的
        for(int i=bi; i < pageBtns.length; ++i){
            pageBtns[i].setVisible(false);
        }

        if(totalPages > 0)
            pageBtns[curBtnPos].setEnabled(false);
    }
}

MyMessage.class

public class MyMessage{
    private String ccontent;
    private String commentid;
    public String getCcontent() {
        return ccontent;
    }
    public void setCcontent(String ccontent) {
        this.ccontent = ccontent;
    }
    public String getCommentid() {
        return commentid;
    }
    public void setCommentid(String commentid) {
        this.commentid = commentid;
    }
}

MyPage.class

public class MyPage{
    private List<MyMessage> content;
    private boolean first;
    private boolean last;
    private int number;
    private int numberOfElements;
    private int size;
    private String totalElements;
    private String sort;

    public String getSort() {
        return sort;
    }

    public void setSort(String sort) {
        this.sort = sort;
    }

    public List<MyMessage> getContent() {
        return content;
    }

    public void setContent(List<MyMessage> content) {
        this.content = content;
    }

    public boolean isFirst() {
        return first;
    }

    public void setFirst(boolean first) {
        this.first = first;
    }

    public boolean isLast() {
        return last;
    }

    public void setLast(boolean last) {
        this.last = last;
    }

    public int getNumber() {
        return number;
    }

    public void setNumber(int number) {
        this.number = number;
    }

    public int getNumberOfElements() {
        return numberOfElements;
    }

    public void setNumberOfElements(int numberOfElements) {
        this.numberOfElements = numberOfElements;
    }

    public int getSize() {
        return size;
    }

    public void setSize(int size) {
        this.size = size;
    }

    public String getTotalElements() {
        return totalElements;
    }

    public void setTotalElements(String totalElements) {
        this.totalElements = totalElements;
    }

    public int getTotalPages() {
        return totalPages;
    }

    public void setTotalPages(int totalPages) {
        this.totalPages = totalPages;
    }

    private int totalPages;
}

　　实现思路：

1. 首先看一下后台的json数据的格式（其中message的值是spring Data JPA分页查询结果的json）

{"success":true,"message":{"content":[{"ccontent":"hjz 2016-38-11 15:38:21*****宋体|12|0-0-0| *****0$$$$$70#####","commentid":"8ae45d92549da2a801549ec092ce001f"},{"ccontent":"hjz 2016-38-11 15:38:10*****宋体|12|0-0-0|哇哇 *****2$$$$$55#####","commentid":"8ae45d92549da2a801549ec068c7001e"}],"first":true,"last":false,"number":0,"numberOfElements":2,"size":2,"sort":{},"totalElements":8,"totalPages":4}}

2. 将“message”对应的值转换成MyPage对象，因为MyPage中有一个List<MyMessage>,如果属性中含有复杂的类型，当其中属性有类似List , Map ,ArrayList、自定义的类型，如List<MyMessage> content, 普通的转换会报错：java.lang.ClassCastException: net.sf.ezmorph.bean.MorphDynaBean cannot be cast to XXX,在JSONObject.toBean的时候如果转换的类中有集合,可以先定义Map<String, Class> classMap = new HashMap<String, Class>();在classMap中put你要转换的类中的集合名 。本例中需要将“content”对应的值转换成 MyMessage对象。

//data为后台的json串
JSONObject result = JSONObject.fromObject(data);
if((Boolean) result.get("success")){//分页显示
    JSONObject message = JSONObject.fromObject(result.get("message"));
    Map<String, Class<?>> classMap = new HashMap<String, Class<?>>();
    classMap.put("content", MyMessage.class);
    MyPage myPage = (MyPage) JSONObject.toBean(message, MyPage.class, classMap);
    this.updatePage(myPage);
}

3.然后通过分页的信息，简单的实现分页按钮，详情看MyPagePanel.java