public void select1(String name,String dbname,String tablename, List<String> columns) throws IOException, NullPointerException{ Table table= getTable(name,dbname,tablename); if (table == null) { return; } table.selects(name,dbname,tablename,columns); }诊断一下错误原因

这段代码本身没有错误。但是如果你使用了其中的一些方法或变量，而这些方法或变量出现了错误，那么就会导致这段代码出现问题。

可能的错误原因包括：

1. getTable(name, dbname, tablename) 方法返回了一个 null，导致 table 变量也为 null。这可能是因为数据库、表、或者行不存在，或者参数传递错误。

2. selects(name,dbname,tablename,columns) 方法出现了错误，导致该方法无法正常执行。这可能是因为该方法没有被正确实现，或者参数传递错误。

3. 参数传递错误，例如 name、dbname、tablename 或 columns 参数传递错误。

你可以检查代码中调用这些方法或变量的部分，看看是否存在上述问题。如果仍然无法解决，请提供更多的代码或者错误信息，以便我能够更好地帮助你。

相关问题

优化这段代码public static void readExcel(String fileName) { List<Version> versions = EasyExcel.read(fileName, Version.class, null).sheet("版本号").doReadSync(); List<TableInfo> tableInfoList = EasyExcel.read(fileName, TableInfo.class, null).sheet("数据库&数据表").doReadSync(); List<TableField> tableFieldList = EasyExcel.read(fileName, TableField.class, null).sheet("字段").doReadSync(); List<HopIndex> hopIndexList = EasyExcel.read(fileName, HopIndex.class, null).sheet("跳数索引").doReadSync(); Map<String, List<TableInfo>> tableInfoMap = tableInfoList.stream().collect(Collectors.groupingBy(TableInfo::getEnDataBaseName)); Map<String, List<TableField>> tableFieldMap = tableFieldList.stream().collect(Collectors.groupingBy(TableField::getEnTableName)); Map<String, List<HopIndex>> hopIndexMap = hopIndexList.stream().collect(Collectors.groupingBy(HopIndex::getEnTableName)); List<TableInfo> tableInfos1 = new ArrayList<>(); List<TableInfo> tableInfos2 = new ArrayList<>(); tableInfoMap.forEach((dbName, tableList) -> { if (tableList.size() < 200) { tableInfos1.addAll(tableList); } else { tableInfos2.addAll(tableList); } }); List<TableField> tableFields = new ArrayList<>(); List<HopIndex> hopIndex = new ArrayList<>(); for (TableInfo tableInfo : tableInfos1) { String enTableName = tableInfo.getEnTableName(); tableFields.addAll(tableFieldMap.get(enTableName)); List<HopIndex> hops = hopIndexMap.get(enTableName); if (hops !=null){ hopIndex.addAll(hops); } } String name = filepath + File.separator + "明细层_V1.0_" + DateUtil.date().toString(DatePattern.PURE_DATE_PATTERN) + "1.xls"; ExcelWriter excelWriter = EasyExcel.write(name).build(); ExcelUtil.writerExcel(excelWriter, "版本号", Version.class, versions); ExcelUtil.writerExcel(excelWriter, "数据库&数据表", TableInfo.class, tableInfos1); ExcelUtil.writerExcel(excelWriter, "字段", TableField.class, tableFields); ExcelUtil.writerExcel(excelWriter, "跳数索引", HopIndex.class, hopIndex); ExcelUtil.close(excelWriter); tableFields.clear(); hopIndex.clear(); for (TableInfo tableInfo : tableInfos2) { String enTableName = tableInfo.getEnTableName(); tableFields.addAll(tableFieldMap.get(enTableName)); List<HopIndex> hops = hopIndexMap.get(enTableName); if (hops !=null){ hopIndex.addAll(hops); } } name = filepath + File.separator + "明细层_V1.0" + DateUtil.date().toString(DatePattern.PURE_DATE_PATTERN) + "_2.xls"; excelWriter = EasyExcel.write(name).build(); ExcelUtil.writerExcel(excelWriter, "版本号", Version.class, versions); ExcelUtil.writerExcel(excelWriter, "数据库&数据表", TableInfo.class, tableInfos2); ExcelUtil.writerExcel(excelWriter, "字段", TableField.class, tableFields); ExcelUtil.writerExcel(excelWriter, "跳数索引", HopIndex.class, hopIndex); ExcelUtil.close(excelWriter); }

这段代码可以进行如下优化：

1. 避免重复读取 Excel 文件。可以将读取 Excel 文件的操作提取出来，作为一个公共方法，然后在需要使用这些数据的地方调用该方法，避免重复读取 Excel 文件。

2. 使用 lambda 表达式和流式操作，简化代码。例如，可以使用 stream().filter() 方法替换原来的 if...else 语句。

3. 避免重复创建对象。例如，可以将 tableFields 和 hopIndex 改为局部变量，避免重复创建。

4. 使用 StringBuilder 拼接字符串，避免重复创建字符串对象。

下面是优化后的代码：

public static void readExcel(String fileName) {
    List<Version> versions = readExcelSheet(fileName, Version.class, "版本号");
    List<TableInfo> tableInfoList = readExcelSheet(fileName, TableInfo.class, "数据库&数据表");
    List<TableField> tableFieldList = readExcelSheet(fileName, TableField.class, "字段");
    List<HopIndex> hopIndexList = readExcelSheet(fileName, HopIndex.class, "跳数索引");

    Map<String, List<TableInfo>> tableInfoMap = tableInfoList.stream()
            .collect(Collectors.groupingBy(TableInfo::getEnDataBaseName));
    Map<String, List<TableField>> tableFieldMap = tableFieldList.stream()
            .collect(Collectors.groupingBy(TableField::getEnTableName));
    Map<String, List<HopIndex>> hopIndexMap = hopIndexList.stream()
            .collect(Collectors.groupingBy(HopIndex::getEnTableName));

    List<TableInfo> tableInfos1 = new ArrayList<>();
    List<TableInfo> tableInfos2 = new ArrayList<>();

    tableInfoMap.forEach((dbName, tableList) -> {
        if (tableList.size() < 200) {
            tableInfos1.addAll(tableList);
        } else {
            tableInfos2.addAll(tableList);
        }
    });

    List<TableField> tableFields;
    List<HopIndex> hopIndex;

    String name;
    ExcelWriter excelWriter;

    tableFields = new ArrayList<>();
    hopIndex = new ArrayList<>();

    for (TableInfo tableInfo : tableInfos1) {
        String enTableName = tableInfo.getEnTableName();
        tableFields.addAll(tableFieldMap.get(enTableName));
        hopIndexMap.getOrDefault(enTableName, Collections.emptyList()).forEach(hopIndex::add);
    }

    name = new StringBuilder()
            .append(filepath)
            .append(File.separator)
            .append("明细层_V1.0_")
            .append(DateUtil.date().toString(DatePattern.PURE_DATE_PATTERN))
            .append("1.xls")
            .toString();

    excelWriter = EasyExcel.write(name).build();
    ExcelUtil.writerExcel(excelWriter, "版本号", Version.class, versions);
    ExcelUtil.writerExcel(excelWriter, "数据库&数据表", TableInfo.class, tableInfos1);
    ExcelUtil.writerExcel(excelWriter, "字段", TableField.class, tableFields);
    ExcelUtil.writerExcel(excelWriter, "跳数索引", HopIndex.class, hopIndex);
    ExcelUtil.close(excelWriter);

    tableFields.clear();
    hopIndex.clear();

    for (TableInfo tableInfo : tableInfos2) {
        String enTableName = tableInfo.getEnTableName();
        tableFields.addAll(tableFieldMap.get(enTableName));
        hopIndexMap.getOrDefault(enTableName, Collections.emptyList()).forEach(hopIndex::add);
    }

    name = new StringBuilder()
            .append(filepath)
            .append(File.separator)
            .append("明细层_V1.0")
            .append(DateUtil.date().toString(DatePattern.PURE_DATE_PATTERN))
            .append("_2.xls")
            .toString();

    excelWriter = EasyExcel.write(name).build();
    ExcelUtil.writerExcel(excelWriter, "版本号", Version.class, versions);
    ExcelUtil.writerExcel(excelWriter, "数据库&数据表", TableInfo.class, tableInfos2);
    ExcelUtil.writerExcel(excelWriter, "字段", TableField.class, tableFields);
    ExcelUtil.writerExcel(excelWriter, "跳数索引", HopIndex.class, hopIndex);
    ExcelUtil.close(excelWriter);
}

private static <T> List<T> readExcelSheet(String fileName, Class<T> clazz, String sheetName) {
    return EasyExcel.read(fileName, clazz, null)
            .sheet(sheetName)
            .doReadSync();
}

<?php // 数据库连接参数 $host = "localhost"; $username = "root"; $password = "123456"; $dbname = "itcast"; // 连接数据库 $db = new PDO("mysql:host={$host};dbname={$dbname}", $username, $password); // 查询员工列表 $sql = "SELECT * FROM employees"; $stmt = $db->prepare($sql); $stmt->execute(); $employees = $stmt->fetchAll(PDO::FETCH_ASSOC); // 输出员工列表 echo "<table>"; echo "<thead><tr><th>ID</th><th>姓名</th><th>性别</th><th>入职日期</th><th>地址</th><th>电话</th></tr></thead>"; echo "<tbody>"; foreach ($employees as $employee) { echo "<tr><td>{$employee['id']} </td><td>{$employee['name']} </td><td>{$employee['gender']} </td><td>{$employee['hire_date']} </td><td>{$employee['address']}</td> <td>{$employee['phone']}</td></tr> "; } echo "</tbody>"; echo "</table>"; ?>添加一个更改按钮

好的，你可以在表头中添加一个“操作”列，然后在每个员工行中添加一个“更改”按钮。代码如下：

<?php 
// 数据库连接参数
$host = "localhost";
$username = "root";
$password = "123456";
$dbname = "itcast";

// 连接数据库
$db = new PDO("mysql:host={$host};dbname={$dbname}", $username, $password);

// 查询员工列表
$sql = "SELECT * FROM employees";
$stmt = $db->prepare($sql);
$stmt->execute();
$employees = $stmt->fetchAll(PDO::FETCH_ASSOC);

// 输出员工列表
echo "<table>";
echo "<thead><tr><th>ID</th><th>姓名</th><th>性别</th><th>入职日期</th><th>地址</th><th>电话</th><th>操作</th></tr></thead>";
echo "<tbody>";
foreach ($employees as $employee) {
    echo "<tr><td>{$employee['id']}</td><td>{$employee['name']}</td><td>{$employee['gender']}</td><td>{$employee['hire_date']}</td><td>{$employee['address']}</td><td>{$employee['phone']}</td>";
    echo "<td><button onclick='editEmployee({$employee['id']})'>更改</button></td></tr>";
}
echo "</tbody>";
echo "</table>";
?>

<script>
function editEmployee(id) {
    // 弹出一个对话框来更改员工信息
    // 这里留给你自己实现
}
</script>

这里我们添加了一个操作列，并在每行中添加了一个更改按钮，点击该按钮会触发 `editEmployee` 函数，你需要在该函数中实现弹出一个对话框来更改员工信息的功能。