java - java 1.6 我想动态创建java POJO类

Question

我想动态创建 java POJO 类

以下是要求：

我有一个方法，它接受参数 classname 和 map 。映射键将是原始类型，映射值将是变量

create Class(String ClassName, HashMap map) 
{
}

调用此方法时，它应该创建一个具有指定名称的 .java 文件，并使用传递的 hashmap 创建 POJO 并将其存储在某个位置。

你们能帮我解决这个问题吗？

我希望我能清楚地提出我的问题。

谢谢。

Answer 1

假设您要生成 Java 源代码并将其保存到.java文件中，您只需要遍历映射并在需要时输出字段定义和 setter/getter。

public String generateJava(String className, Map<String, Object> map) {
    StringBuffer b = new StringBuffer("public class ").append(className).append(" {\n");
    // first fields
    for (Entry<String, Object> field: map.entrySet()) {
       String name = field.getKey();
       String type = field.getValue().getClass().getName();
       b.append("\tprivate ").append(type).append(" ").append(name).append(";\n");
    }
    // then getters and setters
    for (Entry<String, Object> field: map.entrySet()) {
       String name = field.getKey();
       String type = field.getValue().getClass().getName();
       b.append("\n\n");
       // getter.   
       b.append("\tpublic ").append(type).append(" get").append(name.substring(0, 1).toUpperCase()).append(name.substring(1)).append("() {\n\t\t");
       b.append("return this.").append(name).append(";\n\t}"); 
       // setter.   
       b.append("\tpublic void").append(" set").append(name.substring(0, 1).toUpperCase()).append(name.substring(1)).append("(").append(type).append(" ").append(name).append(") {\n\t\t");
       b.append("this.").append(name).append(" = ").append(name).append(";\n\t}"); 
    }
    return b.append("\n}").toString();
}

Answer 2

public class MapFirst
{
    public static void createClass (
        String className, Map <Class<?>, String> fields) throws IOException
    {
        StringBuilder builder = new StringBuilder ();

        String packageName;
        int idx = className.lastIndexOf ('.');
        if (idx >= 0)
        {
            packageName = className.substring (0, idx);
            className = className.substring (idx + 1);
        }
        else packageName = null;

        if (packageName != null)
            builder.append ("package ").append (packageName).append (";\n");

        builder.append ("\n");

        builder.append ("public class ").append (className).append ("\n");

        builder.append ("{\n");

        boolean flag = false;
        for (Map.Entry <Class <?>, String> field: fields.entrySet ())
        {
            Class <?> type = field.getKey ();
            String name = field.getValue ();
            String nameCapitalized = Character.toUpperCase (name.charAt (0)) + name.substring (1);

            if (flag) builder.append ("\n");
            flag = true;
            builder.append ("    private ").append (type).append (" ").append (name).append (";\n");
            builder.append ("\n");
            builder.append ("    public ").append (type).append (" get").append (nameCapitalized).append (" ()\n");
            builder.append ("    {\n");
            builder.append ("        return ").append (name).append (";\n");
            builder.append ("    }\n");
            builder.append ("\n");
            builder.append ("    public void set").append (nameCapitalized).append (" (").append (type).append (" ").append (name).append (")\n");
            builder.append ("    {\n");
            builder.append ("        this.").append (name).append (" = ").append (name).append (";\n");
            builder.append ("    }\n");
        }

        builder.append ("}\n");

        File dir = new File (
            packageName.replaceAll (
                "\\.",
                Matcher.quoteReplacement (System.getProperty ("file.separator"))));

        dir.mkdirs ();

        BufferedWriter writer = new BufferedWriter (
            new OutputStreamWriter (
                new FileOutputStream (
                    new File (dir, className + ".java"))));

        writer.write (builder.toString ());
        writer.close ();
    }

    public static void main (String [] args) throws Exception
    {
        Map <Class <?>, String> fields = new HashMap <Class<?>, String> ();
        fields.put (int.class, "foo");
        fields.put (double.class, "bar");
        createClass ("my.pkg.MyClass", fields);
    }
}