java - 无法创建 Java 列表

Question

我想使用 this编写代码并创建 JSF 2.0 表。

这是托管 bean 的 Java 代码:

import java.io.Serializable;
import javax.enterprise.context.SessionScoped;
// or import javax.faces.bean.SessionScoped;
import javax.inject.Named;
/* include SQL Packages */
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.HashMap;
import javax.annotation.PostConstruct;
import javax.sql.DataSource;
import javax.annotation.Resource;
import javax.faces.context.FacesContext;
import javax.inject.Inject;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;
// or import javax.faces.bean.ManagedBean; 
import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;

import javax.annotation.PostConstruct;
import javax.faces.bean.ManagedBean;
import javax.faces.bean.ViewScoped;
import javax.faces.model.DataModel;
import javax.faces.model.ListDataModel;

import org.glassfish.osgicdi.OSGiService;

@Named("ApplicationController")
@SessionScoped
public class Application implements Serializable {

    private List<Item> list;
    private transient DataModel<Item> model;
    private Item item = new Item();
    private boolean edit;

    @PostConstruct
    public void init() {
        // list = dao.list();
        // Actually, you should retrieve the list from DAO. This is just for demo.
        list = new ArrayList<Item>();
        list.add(new Item(1L, "item1"));
        list.add(new Item(2L, "item2"));
        list.add(new Item(3L, "item3"));
    }

    public void add() {
        // dao.create(item);
        // Actually, the DAO should already have set the ID from DB. This is just for demo.
        item.setId(list.isEmpty() ? 1 : list.get(list.size() - 1).getId() + 1);
        list.add(item);
        item = new Item(); // Reset placeholder.
    }

    public void edit() {
        item = model.getRowData();
        edit = true;
    }

    public void save() {
        // dao.update(item);
        item = new Item(); // Reset placeholder.
        edit = false;
    }

    public void delete() {
        // dao.delete(item);
        list.remove(model.getRowData());
    }

    public List<Item> getList() {
        return list;
    }

    public DataModel<Item> getModel() {
        if (model == null) {
            model = new ListDataModel<Item>(list);
        }

        return model;
    }

    public Item getItem() {
        return item;
    }

    public boolean isEdit() {
        return edit;
    }

}

将代码导入 Netbeans 时出现此问题:

如何声明 Java 列表才能工作？

祝福

编辑我这样编辑代码:

import java.io.Serializable;
import javax.enterprise.context.SessionScoped;
// or import javax.faces.bean.SessionScoped;
import javax.inject.Named;
/* include SQL Packages */
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.HashMap;
import javax.annotation.PostConstruct;
import javax.sql.DataSource;
import javax.annotation.Resource;
import javax.faces.context.FacesContext;
import javax.inject.Inject;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;
// or import javax.faces.bean.ManagedBean; 
import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;

import javax.annotation.PostConstruct;
import javax.faces.bean.ManagedBean;
import javax.faces.bean.ViewScoped;
import javax.faces.model.DataModel;
import javax.faces.model.ListDataModel;

import org.glassfish.osgicdi.OSGiService;

@Named("ApplicationController")
@SessionScoped
public class Application implements Serializable {

    public Application() {
    }    

    private List<Application> list;
    private transient DataModel<Application> model;
    private Application item = new Application();
    private boolean edit;

    private Application(long l, String string) {
        throw new UnsupportedOperationException("Not yet implemented");
    }

    @PostConstruct
    public void init() {
        // list = dao.list();
        // Actually, you should retrieve the list from DAO. This is just for demo.
        list = new ArrayList<Application>();
        list.add(new Application(1L, "item1"));
        list.add(new Application(2L, "item2"));
        list.add(new Application(3L, "item3"));
    }

    public void add() {
        // dao.create(item);
        // Actually, the DAO should already have set the ID from DB. This is just for demo.
        item.setId(list.isEmpty() ? 1 : list.get(list.size() - 1).getId() + 1);
        list.add(item);
        item = new Application(); // Reset placeholder.
    }

    public void edit() {
        item = model.getRowData();
        edit = true;
    }

    public void save() {
        // dao.update(item);
        item = new Application(); // Reset placeholder.
        edit = false;
    }

    public void delete() {
        // dao.delete(item);
        list.remove(model.getRowData());
    }

    public List<Application> getList() {
        return list;
    }

    public DataModel<Application> getModel() {
        if (model == null) {
            model = new ListDataModel<Application>(list);
        }

        return model;
    }

    public Application getItem() {
        return item;
    }

    public boolean isEdit() {
        return edit;
    }

    private void setId(int i) {
        throw new UnsupportedOperationException("Not yet implemented");
    }

    private int getId() {
        throw new UnsupportedOperationException("Not yet implemented");
    }

}

你看到任何错误了吗？

Answer 1

您必须定义 Item 类。

更新:

保持代码的第一种形式。您应该有一个 Item 类。

public class Item {
    private long id;
    private String name;
    public Item() {}
    public Item(long id, String name) {
        this.id = id;
        this.name = name;
    }
    //getters and setters for the attributes...
}

现在，在更新后的代码中，您正在使用 Application 对象列表。所以你的 Application 类应该有 2 个 long 和 String 类型的属性:

//annotations here...
public class Application implements Serializable {
    private long id;
    private String name;
    //getters and setters for these attributes...

    public Application() {
        //keep your actual code here
    }

    //we have to add a constructor that receives a long and a String
    //to initialize the attributes values.
    public Application(long id, String name) {
        this.id = id;
        this.name = name;
    }

    //your actual code...
}

第二种选择不是一个好的做法，我建议您将 Backing Bean(托管 Bean)类与您的模型类(在本例中为 Item 类)分开。