如何从Java ArrayList中获取元素

Question

我有一个基本问题。我有这样的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; 
    } 
} 

我试图让使用该Java代码的元素：

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中出现错误。你能告诉我什么是从ArrayList中获取元素的正确方法吗？

祝福

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 

一个侧面说明，用户数据应的UserData，它是一个Java约定为您定义的任何类的第一个字母使用大写字母。

编辑：

我看你是想现在做什么，你想改变你的插入更类似如下：

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

你也将需要进行新的刀片项目和旧项目的更新。

Answer 3

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

Answer 4

您的对象dataList包含userData类型的对象（顺便说一句，应该是UserData）。

当您拨打dataList.get(something)时，应该是一个整数值，并且get方法检索该位置处的对象。

如果要填补的PreparedStatement在列表中的第一个对象，你会做的是：

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

如果你想为每个用户做同样的：

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，你需要使用dataLi从列表中获得你的userdata项目st.get（index），然后从userdata的实例中取出你的字段。

还挺喜欢这个

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

如果你想在你列出你的每个项目，需要循环和indidually执行这些更新每一个项目。

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(); 
    } 

} 

我也巩固了最后的块，因为没有理由在这种情况下有两个。