How to handle multi-level linkage and data federation query of form data in Java?

How to handle multi-level linkage and data federation query of form data in Java?

In web application development, multi-level linkage of form data and joint data query are very common requirements. As a widely used programming language, Java provides rich functions and tools when dealing with these requirements. This article will introduce how to handle multi-level linkage and data federation query of form data in Java, and provide corresponding code examples.

1. Multi-level linkage

Multi-level linkage means that when the user selects an option in the first-level drop-down box, the content of the next-level drop-down box will change according to the option selected by the user. This is very common in scenarios such as city and region selection, product category selection, etc. In Java, multi-level linkage can be achieved through the following steps:

1. Define relevant entity classes and database tables: According to business needs, define corresponding entity classes and database tables, such as defining City and District. entity class and create the corresponding database table.

public class City {
    private int id;
    private String name;
    // getter和setter方法
}

public class District {
    private int id;
    private String name;
    private int cityId;
    // getter和setter方法
}

2. Database query: Obtain the data of the first-level drop-down box through database query.

public List<City> getAllCities() {
    // 连接数据库，执行查询语句获取City表中的所有记录，并将结果封装到City对象中
    // 返回City对象的List集合
}

3. Get the data of the next-level drop-down box based on the user's selection: by monitoring the selection event of the first-level drop-down box, get the option selected by the user when the selection changes, and then based on the selection The option queries the data of the next-level drop-down box.

public List<District> getDistrictsByCityId(int cityId) {
    // 连接数据库，执行查询语句获取District表中符合条件的记录，并将结果封装到District对象中
    // 返回District对象的List集合
}

4. Use Ajax to obtain data on the front-end page: Use Ajax technology to dynamically display the data queried on the back-end in the front-end page, so that users can see the options of the next-level drop-down box. .

<script type="text/javascript">
    // 监听一级下拉框的选择事件
    $("#city").change(function() {
        var cityId = $(this).val();
        // 使用Ajax将cityId发送到后端处理，并将返回的数据动态展示在下一级下拉框中
        $.ajax({
            url: "getDistrictsByCityId",
            data: {cityId: cityId},
            success: function(data) {
                // 将data中的选项动态展示在下一级下拉框中
            }
        });
    });
</script>

2. Data joint query

Data joint query refers to querying data in the database simultaneously based on multiple conditions. In Java, data joint query can be implemented through connection query, conditional query, etc. of SQL statements. The following is a simple example:

1. Write SQL statements: Write corresponding SQL statements according to business needs to implement the logic of data federation query.

SELECT * FROM table1, table2 WHERE table1.column1 = table2.column2 AND table1.column3 = 'xxx';

2. Result set processing: By executing SQL statements and obtaining the result set, process the result set and extract the required data.

public class DatabaseUtil {
    public List<Data> queryData() {
        Connection conn = null;
        PreparedStatement stmt = null;
        ResultSet rs = null;
        List<Data> dataList = new ArrayList<>();
        
        try {
            conn = getConnection();
            String sql = "SELECT * FROM table1, table2 WHERE table1.column1 = table2.column2 AND table1.column3 = ?";
            stmt = conn.prepareStatement(sql);
            stmt.setString(1, "xxx");
            rs = stmt.executeQuery();
            
            while (rs.next()) {
                Data data = new Data();
                // 从结果集中获取数据并封装到Data对象中
                dataList.add(data);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            close(conn, stmt, rs);
        }
        
        return dataList;
    }
}

The above are the basic steps and code examples for processing multi-level linkage and data federation query of form data. In actual applications, corresponding technologies and tools are selected according to specific business needs and frameworks, and various functions of Java are flexibly used to process multi-level linkage and joint data query of form data to achieve richer and more flexible Web applications.

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