Java combines EasyExcel to build complex multi-level table headers

In Java development, building complex multi-level headers is a common and challenging task when working with Excel files. This article will introduce in detail how to easily implement multi-level header building and write data to Excel files through the customized HeaderBuilder class combined with the EasyExcel library.

1. Overall idea

Our goal is to create a flexible and scalable way to build multi-level headers. To do this, we designed a HeaderBuilder class that uses a tree structure to represent header information. Each header node (HeaderNode) can have multiple child nodes, forming a multi-level structure. Finally, by traversing this tree structure, header data in the form of nested lists suitable for EasyExcel is generated.

2. Key code implementation

HeaderNode class

package ;

import ;

import ;
import ;

@Data
public class HeaderNode {
    private String title;
    private List<HeaderNode> children;

    public HeaderNode(String title) {
         = title;
         = new LinkedList<>();
    }

    public HeaderNode addChild(HeaderNode child) {
        (child);
        return this;
    }
}

passaddChildMethods: You can easily add child nodes to the current node and build a tree structure.

HeaderBuilder class

package ;

import .*;

public class HeaderBuilder {
    private final HeaderNode root;

    private HeaderBuilder(HeaderNode root) {
         = root;
    }

    public static HeaderBuilder create(HeaderNode... headerNodes) {
        HeaderNode root = new HeaderNode("ROOT"); // Virtual root node        for (HeaderNode node : headerNodes) {
            (node);
        }
        return new HeaderBuilder(root);
    }

    /**
      * Generate multi-level header structure
      *
      * @return Nested header structure for EasyExcel
      */
    public List<List<String>> build() {
        List<List<String>> result = new ArrayList<>();
        traverse(new LinkedList<>(), root, result);
        return result;
    }


    private void traverse(LinkedList<String> currentPath, HeaderNode node, List<List<String>> result) {
        if (() == null || ().isEmpty()) {
            (new ArrayList<>(currentPath));
            return;
        }
        for (HeaderNode child : ()) {
            (());
            traverse(currentPath, child, result);
            ();
        }
    }
}

The HeaderBuilder class is responsible for managing and generating header structures. It contains a private root property that points to the root node of the header tree structure. The create method is a static factory method used to create a HeaderBuilder instance. It accepts multiple HeaderNodes as parameters and adds these nodes under the virtual ROOT root node.

The build method is the core method, which performs deep-first traversal of the table header tree structure by calling the private traverse method. During the traversal process, the traverse method collects the node name on the current path into the currentPath. When a leaf node (node ​​without child nodes) is encountered, the content of currentPath is added to the result list result, and the header data in the form of nested lists suitable for EasyExcel is finally generated.

Main program class

package ;

import ;
import ;
import ;

import ;
import ;
import ;

public class Main {
    public static void main(String[] args) {
        // Build the header structure        HeaderNode user = new HeaderNode("user")
               .addChild(new HeaderNode("Name"))
               .addChild(new HeaderNode("age"))
               .addChild(new HeaderNode("gender"));
        HeaderNode address = new HeaderNode("address")
               .addChild(new HeaderNode("province"))
               .addChild(new HeaderNode("City"));
        HeaderNode score = new HeaderNode("Fraction");
        List<List<String>> header = (user, address, score).build();

        (header);
        // Prepare data        List<List<String>> data = new ArrayList<>();
        (("Zhang San", "25", "male", "Zhejiang", "Hangzhou", "20"));
        (("Li Si", "30", "female", "Jiangsu", "Nanjing", "20"));
        ExcelWriter excelWriter = ("").build();
        WriteSheet sheet = ()
               .head(header)
               .build();
        (data, sheet);
        ();
    }
}

In the Main class, the tree structure of the table header is first constructed. By creating a HeaderNode instance and calling the addChild method, a multi-level header node related to "user", "address" and "score" is built. Then, use the method to create the HeaderBuilder instance and call the build method to generate the header data in the form of a nested list.

Then, prepare the data to be written to Excel. Finally, use the EasyExcel library to create ExcelWriter and WriteSheet instances, writing the generated table headers and data to an Excel file named.

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