java - java中将ResultSet转换为HashMap的List

Question

我有一个结果集(由存储过程返回)，例如 -

我需要一个 HashMap 列表，HashMap 将由个人(通过名字、姓氏和 Id 的组合来区分)学生记录组成。下图描述了HashMap的结构。

所以，基本上在这个例子中，我需要一个包含 3 个 HashMap 的列表。

您能建议一些有效的方法吗？谢谢!

为什么我需要一个 HashMap 列表？

我需要从此结果集中创建一个 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:

如果我的方法在编码标准或效率方面不正确，请建议我使用不同的方法。

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 来检查它是否与之前的值相同之外，别无选择。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]:

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

Answer 1

更新

提供了从 ResultSet 中提取数据的代码正确地进入 JAXB 使用的对象.

<小时/>

您不需要HashMap和/或List的HashMap创建 xml文件您可以使用 JAXB 轻松完成此操作，前提是您创建了正确的数据对象。

首先，创建classes匹配 xml 中所需的结构.

1. 一个ScoreRecord保存类(class)信息的类，例如类(class)名称和分数。
2. 一个Student包含学生信息的类，例如名字、姓氏和 ScoreRecords 列表对象。
3. 一个StudentGroup类(class)包含属于同一教师组的所有学生

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“按原样”保存数据库中的数据

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;
}

}

创建一个方法来检索数据 List该对象类型的。我假设您已经拥有了 ResultSet 的东西，迭代它并 .add到列表DbStudent对象。

类似于:

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 对其进行排序，迭代它检查是否找到新学生。如果我们找到一个新学生，我们会将前一个学生添加到 Student 列表中对象。该学生已经设定了分数。

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>