轉換的ResultSet到HashMap中的列表中的Java

Question

我有一個結果集（由存儲過程返回）像 -

我需要的HashMap的名單，而HashMap將作出的個人（不同通過FirstName，LastName和Id的組合）學生記錄。下圖將描述HashMap的結構。

所以，基本上在這個例子中，我需要3 HashMap中的列表。

你可以請建議一些有效的方法來做到這一點？謝謝！

爲什麼我需要一個hashmap的列表呢？

我需要從此ResultSet創建一個XML文件。 HashMap列表是我能想到的所需XML結構的最佳方式。

XML結構：

如果我的做法是不是在編碼標準或效率方面是正確的，請建議我不同的方法。

我在想什麼：

我還沒試過。但除了遍歷ResultSet並暫時存儲FirstName，LastName和Id以檢查它是否與之前的值相同以外，無法考慮其他任何內容。如果相同，則將標記數組添加到MarksList，否則將其視爲另一個學生的記錄。我希望可能有不同的方式。

[更新]：

我想我應該用對象的列表，而不是HashMap的列表。但問題仍然是，我如何解釋結果集中的值並將值設置到對象中。

Answer 1

UPDATE

提供的代碼正確地提取從ResultSet數據到由JAXB使用的對象。

---

你並不需要一個HashMap和/或HashMap一個List創建xml文件 你可以用JAXB這樣做很容易，只要你創建正確的數據對象。

首先，創建classes以匹配期望在xml中的結構。

1. a ScoreRecord舉辦課程名稱和標記等課程信息的類。
2. a Student保存學生信息的類，例如名字，姓氏和一個ScoreRecords對象列表。
3. 一個StudentGroup類包含所有屬於同一教師組

的ScoreRecord類學生：

import java.math.BigDecimal; 

import javax.xml.bind.annotation.XmlRootElement; 
import javax.xml.bind.annotation.XmlType; 

@XmlRootElement(name = "Mark") 
@XmlType(propOrder = { "sub", "percent" }) 
public class ScoreRecord { 
    private String sub; 
    private String percent; 

    public void setSub(String sub) { 
     this.sub = sub; 
    } 

    public String getSub() { 
     return sub; 
    } 

    public void setPercent(String percent) { 
     this.percent = percent; 
    } 

    public String getPercent() { 
     return percent; 
    } 
} 

的Student類：

import java.util.List; 

import javax.xml.bind.annotation.XmlElement; 
import javax.xml.bind.annotation.XmlElementWrapper; 
import javax.xml.bind.annotation.XmlRootElement; 
import javax.xml.bind.annotation.XmlType; 

@XmlRootElement(name = "Student") 
@XmlType(propOrder = { "firstName", "lastName", "id", "scoreRecords" }) 
public class Student { 
    private Integer id; 
    private String firstName; 
    private String lastName; 
    private List<ScoreRecord> scoreRecords; 

    public void setId(Integer id) { 
     this.id = id; 
    } 

    @XmlElement(name = "Id") 
    public Integer getId() { 
     return id; 
    } 

    public void setFirstName(String firstName) { 
     this.firstName = firstName; 
    } 

    @XmlElement(name = "FirstName") 
    public String getFirstName() { 
     return firstName; 
    } 

    public void setLastName(String lastName) { 
     this.lastName = lastName; 
    } 

    @XmlElement(name = "LastName") 
    public String getLastName() { 
     return lastName; 
    } 

    public void setScoreRecords(List<ScoreRecord> scoreRecords) { 
     this.scoreRecords = scoreRecords; 
    } 

    @XmlElementWrapper(name = "MarksList") 
    @XmlElement(name = "Mark") 
    public List<ScoreRecord> getScoreRecords() { 
     return scoreRecords; 
    } 
} 

的StudentGroup類：

import java.util.List; 

import javax.xml.bind.annotation.XmlElement; 
import javax.xml.bind.annotation.XmlElementWrapper; 
import javax.xml.bind.annotation.XmlRootElement; 

@XmlRootElement(name = "Records") 
public class StudentGroup { 
    private List<Student> students; 

    public void setStudents(List<Student> students) { 
     this.students = students; 
    } 

    @XmlElement(name = "StudentRecord") 
    public List<Student> getStudents() { 
     return students; 
    } 
} 

現在，創建一個類來保存數據「原樣」從數據庫

public class DbStudent { 
    private String firstName; 
    private String lastName; 
    private Integer id; 
    private String sub; 
    private String percent; 

public DbStudent(String firstName, String lastName, int id, String sub, String percent) { 
    this.firstName = firstName; 
    this.lastName = lastName; 
    this.id = id; 
    this.sub = sub; 
    this.percent = percent; 
} 

public void setFirstName(String firstName) { 
    this.firstName = firstName; 
} 

public String getFirstName() { 
    return firstName; 
} 

public void setLastName(String lastName) { 
    this.lastName = lastName; 
} 

public String getLastName() { 
    return lastName; 
} 

public void setId(Integer id) { 
    this.id = id; 
} 

public Integer getId() { 
    return id; 
} 

public void setSub(String sub) { 
    this.sub = sub; 
} 

public String getSub() { 
    return sub; 
} 

public void setPercent(String percent) { 
    this.percent = percent; 
} 

public String getPercent() { 
    return percent; 
} 

}

創建以檢索該數據作爲該對象類型的List的方法。我假設你已經有了一些獲得ResultSet的東西，將它迭代並將.add添加到DbStudent對象的列表中。

喜歡的東西：

public List<DbStudent> getStudents() throws ClassNotFoundException, SQLException { 
    List<DbStudent> entries = new ArrayList<DbStudent>(); 

    Class.forName(databaseDriver); 
    this.connection = DriverManager.getConnection(connectionString); 

    Statement sttm = this.connection.createStatement(); 
    ResultSet rs = sttm.executeQuery("select * from TMP_STUDENT"); //in your case procedure call 

    if (rs != null) { 
     while (rs.next()) { //add the results into the list 
      entries.add(new DbStudent(rs.getString("FIRSTNAME"), rs.getString("LASTNAME"), rs.getInt("ID"), 
             rs.getString("SUB"), rs.getString("PERCENT"))); 

     } 
     rs.close(); 
    } 

    return entries; 
} 

現在，主要的方法。它包含從數據庫對象列表中提取所有信息的邏輯。基本上我們通過id對它進行排序，通過它來檢查我們是否找到新學生。如果我們找到一個新學生，我們將前一個添加到一個Student對象列表中。這個學生已經有了他的標記集。

public static void main(String[] args) throws JAXBException { 

    //get the data from the database as is 
    OracleConnection myOracleConnection = new OracleConnection(ORACLE_DRIVER, ORACLE_CONN); 
    List<DbStudent> dbStudentList = null; 
    try { 
     dbStudentList = myOracleConnection.getStudents(); //get the list of students from the procedure or query 
     myOracleConnection.CloseConnection(); 
    } catch (ClassNotFoundException e) { 
     e.printStackTrace(); 
     System.out.println("Stopping execution and exiting..."); 
     System.exit(-1); 
    } catch (SQLException e) { 
     e.printStackTrace(); 
     System.out.println("Stopping execution and exiting..."); 
     System.exit(-1); 
    } 

    //sort the list on Id, so we can know when we find a new student 
    Collections.sort(dbStudentList, new Comparator<DbStudent>() { 
      public int compare(DbStudent s1, DbStudent s2) { 
       return s1.getId().compareTo(s2.getId()); 
      } 
     }); 

    List<Student> studentList=new ArrayList<Student>(); //list which will hold all the student objects 

    Integer previousId = 0; //control variable 
    List<ScoreRecord> marksList = new ArrayList<ScoreRecord>(); //list to store the marks for each student   
    Student s = null; 

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

     if(i==dbStudentList.size()-1){ //if we reached the end, no more students after this record, set the marks and add the student to the list 
      s.setScoreRecords(marksList); 
      studentList.add(s); 
     } 

     if (dbStudentList.get(i).getId().compareTo(previousId) != 0) { 
      //new student found 
      if(s!=null){ 
       //if new student found add the previous one to the list after setting the marks 
       s.setScoreRecords(marksList); 
       studentList.add(s); 
      } 
      s = new Student(); //create a new student 
      s.setFirstName(dbStudentList.get(i).getFirstName()); 
      s.setId(dbStudentList.get(i).getId()); 
      s.setLastName(dbStudentList.get(i).getLastName()); 

      ScoreRecord sr = new ScoreRecord(); 
      sr.setSub(dbStudentList.get(i).getSub()); 
      sr.setPercent(dbStudentList.get(i).getPercent()); 

      marksList = new ArrayList<ScoreRecord>(); //reset marks list 
      marksList.add(sr); 
     } else { 
      //same student 
      ScoreRecord sr = new ScoreRecord(); 
      sr.setSub(dbStudentList.get(i).getSub()); 
      sr.setPercent(dbStudentList.get(i).getPercent()); 
      marksList.add(sr); //add mark to existing marks list 
     } 
     previousId=dbStudentList.get(i).getId(); //set the control variable to the new id 
    } 

    StudentGroup sg=new StudentGroup(); //create the student wrapper 
    sg.setStudents(studentList); //add the student list to the wrapper 

    //create xml with JAXB 
    JAXBContext context = JAXBContext.newInstance(StudentGroup.class); 
    Marshaller m = context.createMarshaller(); 
    m.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true); 
    m.marshal(sg, new File(STUDENT_XML)); 
} 

的xml的輸出正是你想要的：

<?xml version="1.0" encoding="UTF-8" standalone="yes"?> 
<Records> 
    <StudentRecord> 
     <FirstName>AA1</FirstName> 
     <LastName>BB1</LastName> 
     <Id>1</Id> 
     <MarksList> 
      <Mark> 
       <sub>Math</sub> 
       <percent>51%</percent> 
      </Mark> 
      <Mark> 
       <sub>Phy</sub> 
       <percent>61%</percent> 
      </Mark> 
      <Mark> 
       <sub>Bio</sub> 
       <percent>61%</percent> 
      </Mark> 
     </MarksList> 
    </StudentRecord> 
    <StudentRecord> 
     <FirstName>AA2</FirstName> 
     <LastName>BB2</LastName> 
     <Id>2</Id> 
     <MarksList> 
      <Mark> 
       <sub>Bio</sub> 
       <percent>62%</percent> 
      </Mark> 
     </MarksList> 
    </StudentRecord> 
    <StudentRecord> 
     <FirstName>AA3</FirstName> 
     <LastName>BB3</LastName> 
     <Id>3</Id> 
     <MarksList> 
      <Mark> 
       <sub>Math</sub> 
       <percent>53%</percent> 
      </Mark> 
      <Mark> 
       <sub>Phy</sub> 
       <percent>63%</percent> 
      </Mark> 
      <Mark> 
       <sub>Chem</sub> 
       <percent>63%</percent> 
      </Mark> 
     </MarksList> 
    </StudentRecord> 
</Records> 

Answer 2

這裏你需要的是正確的數據對象。在這裏它應該是學生記錄內部應該保存得分記錄列表 哪些將有ID，名字，姓氏，scoreRecords（它應該是列表持有主題名稱，標記，％等）。

然後簡單地將其轉換成XML與JAXB

Answer 3

如果排序姓氏和名字你的SQL語句/ StoredProcedure時你並不需要收集整個數據在內存中。 只需迭代您的結果集並收集數據，直到FirstName和LastName發生變化，然後彙總您的子數據和百分比數據並將其直接流式傳輸到文件或dom。等等......

或者更改存儲過程或創建一個新的存儲過程，它已經爲您彙總了數據。