如何从csv文件生成java类 [英] How to generate java class from csv file

问题描述

我有多个csv文件包含大约200到300列，我需要创建pojos与一对一的映射（列太java类字段）。不介意不推荐的事实。
如果你知道一个工具或如何自动地执行这项工作。

I have multiple csv files containing about 200 to 300 columns and I need to create pojos out of them with a mapping of one to one (column too java class field). Never mind the fact that is not recommended. If you know a tool or how to do this automatically please pitch in.

所以你有一个csv文件，包含数千行，第一行包含列的标题。所以我需要，基于第一行（列的头）创建一个包含这些头作为类字段的java类。不要介意实际的数据。我只需要一个带有这些字段的java类。

so you have a csv file, containing thousands of rows with hundreds of columns, the first row contains the header of the columns. SO what I need, based on the first row (header of column) to create a java class that contains those headers as class fields. Never mind the actual data. I just need a java class with those fields

这个帖子有一个问题，但是这是在3年前问过的，所以我猜测已经过时了。

There was a question regarding somewhat this post but this was asked about 3 years ago, so I guess is obsolete.

推荐答案

您可以使用Javassist在运行时生成类：

You can use Javassist to generate classes at runtime:

代码：

public static void main(String[] args) throws Exception {
    String[] fieldNames = null;
    Class<?> rowObjectClass = null;
    try(BufferedReader stream = new BufferedReader(new InputStreamReader(Program.class.getResourceAsStream("file.csv")))) {
        while(true) {
            String line = stream.readLine();
            if(line == null) {
                break;
            }
            if(line.isEmpty() || line.startsWith("#")) {
                continue;
            }
            if(rowObjectClass == null) {
                fieldNames = line.split(",");
                rowObjectClass = buildCSVClass(fieldNames);
            } else {
                String[] values = line.split(",");
                Object rowObject = rowObjectClass.newInstance();
                for (int i = 0; i < fieldNames.length; i++) {
                    Field f = rowObjectClass.getDeclaredField(fieldNames[i]);
                    f.setAccessible(true);
                    f.set(rowObject, values[i]);

                }
                System.out.println(reflectToString(rowObject));
            }
        }
    }
}

private static int counter = 0;
public static Class<?> buildCSVClass(String[] fieldNames) throws CannotCompileException, NotFoundException {
    ClassPool pool = ClassPool.getDefault();
    CtClass result = pool.makeClass("CSV_CLASS$" + (counter++));
    ClassFile classFile = result.getClassFile();
    ConstPool constPool = classFile.getConstPool();
    classFile.setSuperclass(Object.class.getName());
    for (String fieldName : fieldNames) {
        CtField field = new CtField(ClassPool.getDefault().get(String.class.getName()), fieldName, result);
        result.addField(field);
    }
    classFile.setVersionToJava5();
    return result.toClass();
}

public static String reflectToString(Object value) throws IllegalAccessException {
    StringBuilder result = new StringBuilder(value.getClass().getName());
    result.append("@").append(System.identityHashCode(value)).append(" {");
    for (Field f : value.getClass().getDeclaredFields()) {
        f.setAccessible(true);
        result.append("\n\t").append(f.getName()).append(" = ").append(f.get(value)).append(", ");
    }
    result.delete(result.length()-2, result.length());
    return result.append("\n}").toString();
}

资源：

file.csv（classpath）：

file.csv (classpath):

############
foo,bar
############
hello,world
cafe,babe

输出：

CSV_CLASS$0@1324706137 {
    foo = hello, 
    bar = world
}
CSV_CLASS$0@1373076110 {
    foo = cafe, 
    bar = babe
}

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