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Java8使用Function讀取文件

更新時間：2024年12月26日 09:53:18 作者：ByteX

這篇文章主要為大家詳細介紹了Java8如何使用Function讀取文件,文中的示例代碼講解詳細,具有一定的借鑒價值,有需要的小伙伴可以參考一下

首先，我們需要一個 FileCloseAble 類來處理文件寫入操作。

import java.util.ArrayList;
import java.util.function.Consumer;
import java.util.List;

public class FileCloseAble<T> implements AutoCloseable {
    private Consumer<List<T>> writer;
    private int pageSize;
    private List<T> buffer;

    public FileCloseAble(Consumer<List<T>> writer, int pageSize) {
        this.writer = writer;
        this.pageSize = pageSize;
        this.buffer = new ArrayList<>(Math.max(1, pageSize));
    }

    public void add(T element) {
        buffer.add(element);
        if (buffer.size() >= pageSize) {
            flush();
        }
    }

    private void flush() {
        if (!buffer.isEmpty()) {
            writer.accept(new ArrayList<>(buffer));
            buffer.clear();
        }
    }

    @Override
    public void close() {
        flush();
    }
}

FileContext 類來存儲文件的上下文信息。

public class FileContext {
    private File file;
    private Charset charset;
    private int skipHeader;
    private String batchDate;
    private int pageSize;
    private boolean deleteFlag;
    private String filterLineHeader;

    // 構(gòu)造函數(shù)、getter 和 setter 省略

    public File getFile() {
        return file;
    }

    public void setFile(File file) {
        this.file = file;
    }

    public Charset getCharset() {
        return charset;
    }

    public void setCharset(Charset charset) {
        this.charset = charset;
    }

    public int getSkipHeader() {
        return skipHeader;
    }

    public void setSkipHeader(int skipHeader) {
        this.skipHeader = skipHeader;
    }

    public String getBatchDate() {
        return batchDate;
    }

    public void setBatchDate(String batchDate) {
        this.batchDate = batchDate;
    }

    public int getPageSize() {
        return pageSize;
    }

    public void setPageSize(int pageSize) {
        this.pageSize = pageSize;
    }

    public boolean isDeleteFlag() {
        return deleteFlag;
    }

    public void setDeleteFlag(boolean deleteFlag) {
        this.deleteFlag = deleteFlag;
    }

    public String getFilterLineHeader() {
        return filterLineHeader;
    }

    public void setFilterLineHeader(String filterLineHeader) {
        this.filterLineHeader = filterLineHeader;
    }
}

FileHandler 類

import lombok.AllArgsConstructor;
import lombok.Builder;
import lombok.NoArgsConstructor;
import lombok.extern.slf4j.Slf4j;

import java.io.File;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.List;
import java.util.function.BiFunction;
import java.util.function.Consumer;
import java.util.stream.Stream;

@Builder
@AllArgsConstructor
@NoArgsConstructor
@Slf4j
public class FileHandler<T, R> {

    private FileContext context;
    private BiFunction<String, String, T> reader; // 讀邏輯
    private Consumer<List<T>> writer;// 寫邏輯
    private LineFilter lineFilter; // 新增過濾邏輯

    public void execute() throws Exception {
        File file = context.getFile();
        try (
                Stream<String> streams = Files.lines(Paths.get(file.getPath()), context.getCharset());
                FileCloseAble<T> files = new FileCloseAble<>(writer, context.getPageSize())
        ) {
            streams.skip(context.getSkipHeader())
                    .filter(lineFilter.getLinePredicate())
                    .map(e -> reader.apply(e, context.getBatchDate()))
                    .forEach(files::add);
        } catch (Exception e) {
            log.error("解析文件失敗: file: {}, error: {}", file, e);
            throw new Exception("文件處理異常", e);
        } finally {
            deleteFileIfNecessary(file);
        }
    }

    private void deleteFileIfNecessary(File file) {
        if (context.isDeleteFlag() && file.exists()) {
            try {
                boolean deleted = Files.deleteIfExists(file.toPath());
                if (deleted) {
                    log.info("文件已刪除: {}", file);
                } else {
                    log.info("文件不存在，無法刪除: {}", file);
                }
            } catch (Exception e) {
                log.error("刪除文件失敗: file: {}, error: {}", file, e);
            }
        }
    }
}

定義一個過濾函數(shù)接口

定義一個 Predicate 接口，用于表示每一行的過濾邏輯。

import java.util.function.Predicate;

public interface LineFilter {
    Predicate<String> getLinePredicate();
}

實現(xiàn) LineFilter 接口

創(chuàng)建一個實現(xiàn)了 LineFilter 接口的類，用于定義具體的過濾邏輯。

import java.util.function.Predicate;

public class CustomLineFilter implements LineFilter {
    private String filterLineHeader;

    public CustomLineFilter(String filterLineHeader) {
        this.filterLineHeader = filterLineHeader;
    }

    @Override
    public Predicate<String> getLinePredicate() {
        return line -> !line.startsWith(filterLineHeader);
    }
}

使用 FileHandler 類

import java.io.File;
import java.nio.charset.StandardCharsets;
import java.util.List;
import java.util.function.BiFunction;
import java.util.function.Consumer;

public class FileHandlerExample {
    public static void main(String[] args) {
        // 創(chuàng)建文件上下文
        FileContext context = new FileContext();
        File file = new File("D:\\temp\\testwrite.txt");
        context.setFile(file);
        context.setCharset(StandardCharsets.UTF_8);
        context.setSkipHeader(0);
        context.setBatchDate("20220101");
        context.setPageSize(100);
        context.setDeleteFlag(false);

        // 定義解析方法
        BiFunction<String, String, String> reader = (line, batchDate) -> line.trim();

        // 定義寫入方法
        Consumer<List<String>> writer = list -> {
            for (String s : list) {
                System.out.println(s);
            }
        };

        // 創(chuàng)建自定義過濾邏輯
        LineFilter lineFilter = new CustomLineFilter("#");

        // 創(chuàng)建 FileHandler 實例
        FileHandler<String, Void> fileHandler = FileHandler.<String, Void>builder()
                .context(context)
                .reader(reader)
                .writer(writer)
                .lineFilter(lineFilter) // 設(shè)置過濾邏輯
                .build();

        // 執(zhí)行文件處理
        try {
            fileHandler.execute();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

可以愉快的讀寫文件啦

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