java - 如何从 Java ArrayList 中获取元素

Question

我有一个基本问题。我有这个 ArrayList：

@Named("AccountProfileController")
@ViewScoped
public class AccountProfile implements Serializable
{

    @Resource(name = "jdbc/Oracle")
    private DataSource ds;
    private int id;

    // Constructor
    public AccountProfile()
    {
        // get the ID value 
        try
        {
            this.id = Integer.parseInt((String) FacesContext.getCurrentInstance().getExternalContext().getRequestParameterMap().get("id"));
        }
        catch (Exception e)
        {
            this.id = 0;
        }
    }
    // Create List to store user data
    public ArrayList<userdata> dataList = new ArrayList<>();

    public class userdata
    {

        int userid;
        int groupid;
        String specialnumber;
        String username;
        String passwd;
        Date datetochangepasswd;
        String address;
        String stateregion;
        String country;
        String userstatus;
        String telephone;
        Date dateuseradded;
        Date userexpiredate;
        Date dateuserlocked;
        String city;
        String email;
        String description;

        public userdata(int userid, int groupid, String specialnumber, String username, String passwd, Date datetochangepasswd,
                String address, String stateregion, String country, String userstatus, String telephone, Date dateuseradded,
                Date userexpiredate, Date dateuserlocked, String city, String email, String description)
        {

            this.userid = userid;
            this.groupid = groupid;
            this.specialnumber = specialnumber;
            this.username = username;
            this.passwd = passwd;
            this.datetochangepasswd = datetochangepasswd;
            this.address = address;
            this.stateregion = stateregion;
            this.country = country;
            this.userstatus = userstatus;
            this.telephone = telephone;
            this.dateuseradded = dateuseradded;
            this.userexpiredate = userexpiredate;
            this.dateuserlocked = dateuserlocked;
            this.city = city;
            this.email = email;
            this.description = description;
        }

        public String getAddress()
        {
            return address;
        }

        public void setAddress(String address)
        {
            this.address = address;
        }

        public String getCity()
        {
            return city;
        }

        public void setCity(String city)
        {
            this.city = city;
        }

        public String getCountry()
        {
            return country;
        }

        public void setCountry(String country)
        {
            this.country = country;
        }

        public Date getDatetochangepasswd()
        {
            return datetochangepasswd;
        }

        public void setDatetochangepasswd(Date datetochangepasswd)
        {
            this.datetochangepasswd = datetochangepasswd;
        }

        public Date getDateuseradded()
        {
            return dateuseradded;
        }

        public void setDateuseradded(Date dateuseradded)
        {
            this.dateuseradded = dateuseradded;
        }

        public Date getDateuserlocked()
        {
            return dateuserlocked;
        }

        public void setDateuserlocked(Date dateuserlocked)
        {
            this.dateuserlocked = dateuserlocked;
        }

        public String getDescription()
        {
            return description;
        }

        public void setDescription(String description)
        {
            this.description = description;
        }

        public String getEmail()
        {
            return email;
        }

        public void setEmail(String email)
        {
            this.email = email;
        }

        public int getGroupid()
        {
            return groupid;
        }

        public void setGroupid(int groupid)
        {
            this.groupid = groupid;
        }

        public String getPasswd()
        {
            return passwd;
        }

        public void setPasswd(String passwd)
        {
            this.passwd = passwd;
        }

        public String getSpecialnumber()
        {
            return specialnumber;
        }

        public void setSpecialnumber(String specialnumber)
        {
            this.specialnumber = specialnumber;
        }

        public String getStateregion()
        {
            return stateregion;
        }

        public void setStateregion(String stateregion)
        {
            this.stateregion = stateregion;
        }

        public String getTelephone()
        {
            return telephone;
        }

        public void setTelephone(String telephone)
        {
            this.telephone = telephone;
        }

        public Date getUserexpiredate()
        {
            return userexpiredate;
        }

        public void setUserexpiredate(Date userexpiredate)
        {
            this.userexpiredate = userexpiredate;
        }

        public int getUserid()
        {
            return userid;
        }

        public void setUserid(int userid)
        {
            this.userid = userid;
        }

        public String getUsername()
        {
            return username;
        }

        public void setUsername(String username)
        {
            this.username = username;
        }

        public String getUserstatus()
        {
            return userstatus;
        }

        public void setUserstatus(String userstatus)
        {
            this.userstatus = userstatus;
        }
    }

    // Getter for the data list
    public ArrayList<userdata> getuserdata()
    {

        return dataList;
    }

    @PostConstruct
    public void initData() throws SQLException
    {
        //     settingsMap = new HashMap<String, String>();

        if (ds == null)
        {
            throw new SQLException("Can't get data source");
        }
        // Initialize a connection to Oracle
        Connection conn = ds.getConnection();

        if (conn == null)
        {
            throw new SQLException("Can't get database connection");
        }
        // With SQL statement get all settings and values
        PreparedStatement ps = conn.prepareStatement("SELECT * from USERS where USERID = ?");
        ps.setInt(1, id);
        try
        {
            //get data from database        
            ResultSet result = ps.executeQuery();
            while (result.next())
            {
                // Put the the data from Oracle into Array List

                dataList.add(new userdata(result.getInt("USERID"),
                        result.getInt("GROUPID"),
                        result.getString("SPECIALNUMBER"),
                        result.getString("USERNAME"),
                        result.getString("PASSWD"),
                        toDate(result.getString("DATETOCHANGEPASSWD")),
                        result.getString("ADDRESS"),
                        result.getString("STATEREGION"),
                        result.getString("COUNTRY"),
                        result.getString("USERSTATUS"),
                        result.getString("TELEPHONE"),
                        toDate(result.getString("DATEUSERADDED")),
                        toDate(result.getString("USEREXPIREDATE")),
                        toDate(result.getString("DATEUSERLOCKED")),
                        result.getString("CITY"),
                        result.getString("EMAIL"),
                        result.getString("DESCRIPTION")));

            }
        }
        finally
        {
            ps.close();
            conn.close();
        }
    }
    // Call Crypto library for password convert into SHA hash
    @Inject
    @OSGiService(dynamic = true, waitTimeout = 5)
    transient CryptoSHA SHA;

    // Convert Password String into SHA hash
    public String passwdConvert(String password) throws NoSuchAlgorithmException
    {
        return SHA.ShaEncryptHash(password);
    }

    // Insert the data into Oracle
    public void saveData() throws SQLException, java.text.ParseException, NoSuchAlgorithmException
    {

        String SqlStatement = null;

        if (ds == null)
        {
            throw new SQLException();
        }

        Connection conn = ds.getConnection();
        if (conn == null)
        {
            throw new SQLException();
        }

        PreparedStatement ps = null;

        try
        {
            conn.setAutoCommit(false);
            boolean committed = false;
            try
            {           /*
                 * insert into Oracle the default system(Linux) time
                 */


                SqlStatement = "UPDATE USERS "
                        + "SET "
                        + "USERID = ?, "
                        + "GROUPID = ?, "
                        + "SPECIALNUMBER = ?, "
                        + "USERNAME = ?, "
                        + "PASSWD = ?, "
                        + "DATETOCHANGEPASSWD = ?, "
                        + "ADDRESS = ?, "
                        + "STATEREGION = ?, "
                        + "COUNTRY = ?, "
                        + "USERSTATUS = ?, "
                        + "TELEPHONE = ?, "
                        + "DATEUSERADDED = ?, "
                        + "USEREXPIREDATE = ?, "
                        + "DATEUSERLOCKED = ?, "
                        + "CITY = ?, "
                        + "EMAIL = ?, "
                        + "DESCRIPTION = ? "
                        + "WHERE USERID = " + id;

                ps = conn.prepareStatement(SqlStatement);

                ps.setInt(1, dataList.get(userid));
                ps.setInt(2, dataList.get(groupid));
                ps.setString(3, dataList.get(specialnumber));
                ps.setString(4, dataList.get(username));
                ps.setString(5, passwdConvert(dataList.get(passwd)));
                ps.setDate(6, toDate(dataList.get(datetochangepasswd)));
                ps.setString(7, dataList.get(address));
                ps.setString(8, dataList.get(stateregion));
                ps.setString(9, dataList.get(country));
                ps.setString(10, dataList.get(userstatus));
                ps.setString(11, dataList.get(telephone));
                ps.setDate(12, toDate(dataList.get(dateuseradded)));
                ps.setDate(13, toDate(dataList.get(userexpiredate)));
                ps.setDate(14, toDate(dataList.get(dateuserlocked)));
                ps.setString(15, dataList.get(city));
                ps.setString(16, dataList.get(email));
                ps.setString(17, dataList.get(description));


                ps.executeUpdate();

                conn.commit();
                committed = true;
            }
            finally
            {
                if (!committed)
                {
                    conn.rollback();
                }
            }
        }
        finally
        {
            /*
             * Release the resources
             */
            ps.close();
            conn.close();
        }

    }
    //!!!! http://stackoverflow.com/questions/11135675/unparseable-date-30-jun-12
    // Convert the Date format

    public Date toDate(String s)
    {
        Date d = null;
        if (s == null || s.trim().isEmpty())
        {
            return d;
        }

        try
        {
            d = Date.valueOf(s);
        }
        catch (Exception x)
        {
            x.printStackTrace();
        }

        return d;
    }
}

我尝试使用此 Java 代码获取元素：

ps.setInt(1, dataList.get(userid));
ps.setInt(2, dataList.get(groupid));
ps.setString(3, dataList.get(specialnumber));
ps.setString(4, dataList.get(username));
ps.setString(5, passwdConvert(dataList.get(passwd)));
ps.setDate(6, toDate(dataList.get(datetochangepasswd)));
ps.setString(7, dataList.get(address));
ps.setString(8, dataList.get(stateregion));
ps.setString(9, dataList.get(country));
ps.setString(10, dataList.get(userstatus));
ps.setString(11, dataList.get(telephone));
ps.setDate(12, toDate(dataList.get(dateuseradded)));
ps.setDate(13, toDate(dataList.get(userexpiredate)));
ps.setDate(14, toDate(dataList.get(dateuserlocked)));
ps.setString(15, dataList.get(city));
ps.setString(16, dataList.get(email));
ps.setString(17, dataList.get(description));

但我在 Netbeans 中遇到错误。你能告诉我从 ArrayList 中获取元素的正确方法是什么吗？

最良好的祝愿

Answer 1

使用for-each loop this is optimize way...

for(userdata obj : dataList){

   System.out.println("User ID :: " + obj.userid);
   System.out.println("Group ID :: " + obj.groupid);
   .
   .
   .

}

使用 for 循环

for(int i =0;i<datalist.size();i++){

       userdate obj=datalist.get(i);
       System.out.println("User ID :: " + obj.userid);
       System.out.println("Group ID :: " + obj.groupid);
       .
       .
       .

    }

Answer 2

ArrayList<userdata> dataList = new ArrayList<>();
dataList.add(new userdata(...)); // The ... is for all your params
userdata data = dataList.get(0); // This gets the first element of the list, the one we just added
System.out.println(data.getCity()); // This will print the String called city

附带说明，userdata 应该是 UserData，这是一个 Java 约定，您定义的任何类的第一个字母都使用大写。

编辑：

我知道您现在要做什么，您将希望将插入更改为更像以下内容：

for (userdata data : dataList) {
    ps.setInt(1, data.getUserid());
    ps.setInt(2, data.getGroupid());
    ...
}

此外，您还需要为新项目执行插入，并为旧项目执行更新。

Answer 3

ps.setInt(1, dataList.get(i).getUserId());

Answer 4

您的对象 dataList 包含类型为 userData 的对象（顺便说一下，应该是 UserData）。

当您调用dataList.get(something)时，该值应该是一个整数值，并且该get方法会在该位置检索对象。

如果想用列表中的第一个对象填充 PreparedStatement，你会做的是：

UserData user = dataList.get(0);
ps.setInt(1, user.getUserId())
...

如果您想为每个用户做同样的事情：

for(userdata obj : dataList){

    ps.setInt(1, obj.userid);
    ...

    //do something with PS for this object.
}

Answer 5

试试这个

for(userdata datum : dataList)
{ //for each userdata instance in dataList collection
            ps.setInt(1, datum.userid); //ps.setInt(1, datum.getUserid());
            ps.setInt(2, datum.groupid);
            ps.setString(3, datum.specialnumber);
            //... you get the idea
}

基本上，您需要使用 dataList.get(index) 从列表中获取您的用户数据项，然后从用户数据的实例中提取您的字段。

有点像这样

for(int i = 0; i < dataList.size(); i++)
{
            ps.setInt(1, dataList.get(i).getUserid()); //ps.setInt(1, datum.getUserid());
            ps.setInt(2, dataList.get(i).getGroupId());
            ps.setString(3, dataList.get(i).specialnumber);
            //... you get the idea
}

Answer 6

如果您尝试更新列表中的每个项目，则需要遍历每个项目并单独执行它们。

 public void saveData() throws SQLException, java.text.ParseException, NoSuchAlgorithmException {
    String SqlStatement = null;
    if (ds == null) {
        throw new SQLException();
    }

    Connection conn = ds.getConnection();
    if (conn == null) {
        throw new SQLException();
    }

    PreparedStatement ps = null;
    try {
        conn.setAutoCommit(false);
        boolean committed = false;
            //removed the userid as that is used in the where to determine what record to update
            //so it will be the same
            SqlStatement = "UPDATE USERS "
                    + "SET "
                    + "GROUPID = ?, "
                    + "SPECIALNUMBER = ?, "
                    + "USERNAME = ?, "
                    + "PASSWD = ?, "
                    + "DATETOCHANGEPASSWD = ?, "
                    + "ADDRESS = ?, "
                    + "STATEREGION = ?, "
                    + "COUNTRY = ?, "
                    + "USERSTATUS = ?, "
                    + "TELEPHONE = ?, "
                    + "DATEUSERADDED = ?, "
                    + "USEREXPIREDATE = ?, "
                    + "DATEUSERLOCKED = ?, "
                    + "CITY = ?, "
                    + "EMAIL = ?, "
                    + "DESCRIPTION = ? "
                    + "WHERE USERID = " + ?; //also changed this to be a parameter

            ps = conn.prepareStatement(SqlStatement);

            for (userdata data: datalist) {
              ps.setInt(1, dataList.getGroupid());
              ps.setString(2, dataList.getSpecialnumber());
              ...
              //continue setting the others variables
              //the last on will be the userid in the where clause
              ps.setInt(17, dataList.getUserId());
              //execute the update
              ps.executeUpdate();
            }
            //now we commit since they have all ran. We want an all or nothing update
            //meaning if one fails, nothing is updated
            conn.commit();
            committed = true;

    }
    finally
    { 
        if (!committed){
          conn.rollback();
        }
        ps.close();
        conn.close();
    }

}

我还合并了 finally 块，因为在这种情况下没有理由有两个。