Question

我有一个结果集（由存储过程返回），如 -

enter image description here

我需要一个HashMap列表，而HashMap将由个人（不同于FirstName，LastName和Id的组合）学生记录组成。下图将描述HashMap的结构。

enter image description here

所以，基本上在这个例子中，我需要一个3个HashMap的列表。

请你建议一些有效的方法吗？谢谢！

为什么我需要一个hashmap列表呢？

我需要从这个ResultSet创建一个XML文件。 HashMap列表是我能想到的所需XML结构的最佳方式。

XML结构：

enter image description here

如果我的方法在编码标准或效率方面不正确，请建议我采用不同的方法。

我在想什么：

我还没试过。但除了迭代ResultSet并临时存储FirstName，LastName和Id以检查它是否与之前的值相同之外，我无法想到其他任何事情。如果相同，则将标记数组添加到MarksList，否则将其视为另一个学生的记录。我希望可能有不同的方式。

[更新]：

我想我应该使用对象列表，而不是HashMap列表。但问题仍然是，我如何解释结果集中的值并将值设置到对象中。

Answer 1

更新

提供代码，将ResultSet中的数据正确提取到JAXB使用的对象中。

您不需要HashMap和/或List HashMap来创建xml文件如果您创建了正确的数据对象，则可以使用JAXB轻松完成此操作。

首先，创建classes以匹配xml中所需的结构。

一个ScoreRecord课程，其中包含课程名称和标记等课程信息。
一个Student类，其中包含学生信息，如名字，姓氏和ScoreRecords个对象列表。
一个StudentGroup课程，其中包含属于同一教师团体的所有学生

ScoreRecord类：

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;
    }
}

Student类：

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;
    }
}

StudentGroup类：

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;
    }
}

现在，创建一个类来保存数据＆＃34;按原样＃34;来自数据库

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;
}

}

创建一种方法，将数据作为此对象类型的List进行检索。我假设您已经拥有获取ResultSet的内容，将其迭代并.add到DbStudent个对象列表。

类似的东西：

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;
}

现在，主要方法。它包含从数据库对象列表中提取所有信息的逻辑。基本上我们按id排序，迭代检查我们是否找到了新学生。如果我们找到一个新学生，我们会将前一个学生添加到Student个对象列表中。这名学生已经有了他的分数。

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));
}

xml的输出正是您想要的：

<?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

这里需要的是正确的数据对象。这里应该是学生记录内部应该保留记分列表的记录它将具有id，FirstName，LastName，scoreRecords（它应该是列出主题名称，标记，％等）。

然后只需使用JAXB

将其转换为XML

Answer 3

如果按LastName和FirstName对sql-statement / storedprocedure进行排序，则不需要在内存中收集整个数据。只需迭代结果集并收集数据，直到FirstName和LastName发生更改，然后汇总您的sub和percent数据并将其直接流式传输到文件或dom。等等....
或者更改存储过程或以已经为您聚合数据的方式创建新过程。

将ResultSet转换为java中的HashMap列表

3 个答案: