MyBatis 生成器的表注释

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MyBatis是流行的持久化框架，通过抽象底层的JDBC代码，在类对象和数据库列之间自动映射SQL的参数和结果，以SQL为映射的间接层，实现SQL映射器。MyBatis Generator (MBG) 是一个Mybatis的代码生成器，内省数据库的表，然后自动生成映射表的实体类，并生成CRUD（插入，查询，更新，删除）操作的样板代码。MyBatis，之前所在的公司在用，生成器也在用。虽然生成器大大提供了开发效率，但生成的代码可读性比较低，尤其是自动生成的实体类，如下：

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/**
* This field was generated by MyBatis Generator. This field corresponds to the database column author.book_id
* @mbggenerated  Tue Jan 19 13:37:24 CST 2016
*/
private Integer bookId;

这些自动生成注释，没有实质性信息，其实真正有用的是，设计表时，该字段的用途，即表字段的注释。

addRemarkComments选项

庆幸的是，MyBatis生成器在版本1.3.3中添加了，addRemarkComments选项 [github]，可以在生成的实体类中附带表字段的注释。addRemarkComments官方文档的介绍 [doc]：

This property is used to specify whether MBG will include table and column remarks from db table in the generated comments. The property supports these values:

  • false: This is the default value When the property is false or unspecified, all generated comments will not include table and column remarks from db table when the element was generated.
  • true: When the property is true, table and columns remarks from db table will be added to the generated comments.

Warning: If suppressAllComments option is true, this option will be ignored.

使用方法很简单，只需将MyBatis生成器的配置文件中的commentGenerator节点修改为：

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<commentGenerator>
    <property name="addRemarkComments" value="true" />
</commentGenerator>

自定义注释生成器类

通过addRemarkComments选项生成的实体类的注释不够精简。于是笔者参考MyBatis的默认的注释生成器DefaultCommentGenerator[github]，对其进行改造成如下：

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package com.test.mbg;
 
import java.util.Date;
 
import org.apache.commons.lang3.time.DateFormatUtils;
import org.mybatis.generator.api.IntrospectedColumn;
import org.mybatis.generator.api.IntrospectedTable;
import org.mybatis.generator.api.dom.java.Field;
import org.mybatis.generator.api.dom.java.JavaElement;
import org.mybatis.generator.api.dom.java.Method;
import org.mybatis.generator.api.dom.java.TopLevelClass;
import org.mybatis.generator.config.MergeConstants;
import org.mybatis.generator.internal.DefaultCommentGenerator;
import org.mybatis.generator.internal.util.StringUtility;
 
/**
 * 官方类似的功能见，在版本1.3.3中添加的 addRemarkComments <br>
 * http://www.mybatis.org/generator/configreference/commentGenerator.html <br>
 * https://github.com/mybatis/generator/issues/23
 *
 * @see DefaultCommentGenerator#addRemarkComments
 */
public class RemarksCommentGenerator extends DefaultCommentGenerator {
 
    @Override
    public void addModelClassComment(TopLevelClass topLevelClass, IntrospectedTable introspectedTable) {
        topLevelClass.addJavaDocLine("/**");
 
        String remarks = introspectedTable.getRemarks();
        if (StringUtility.stringHasValue(remarks)) {
            String[] remarkLines = remarks.split(System.getProperty("line.separator"));
            for (String remarkLine : remarkLines) {
                topLevelClass.addJavaDocLine(" * " + remarkLine);
            }
        }
 
        topLevelClass.addJavaDocLine(" * ");
        StringBuilder sb = new StringBuilder();
        sb.append(" * ");
        sb.append(introspectedTable.getFullyQualifiedTable());
        topLevelClass.addJavaDocLine(sb.toString());
        topLevelClass.addJavaDocLine(" *");
        addJavadocTag(topLevelClass, false);
        topLevelClass.addJavaDocLine(" */");
    }
 
    public void addFieldComment(Field field, IntrospectedTable introspectedTable, IntrospectedColumn introspectedColumn) {
        field.addJavaDocLine("/**");
 
        String remarks = introspectedColumn.getRemarks();
        if (StringUtility.stringHasValue(remarks)) {
            String[] remarkLines = remarks.split(System.getProperty("line.separator")); 
            for (String remarkLine : remarkLines) {
                field.addJavaDocLine(" * " + remarkLine);
            }
        }
 
        field.addJavaDocLine(" *");
        StringBuilder sb = new StringBuilder();
        sb.append(" * ");
        sb.append(introspectedTable.getFullyQualifiedTable());
        sb.append('.');
        sb.append(introspectedColumn.getActualColumnName());
        field.addJavaDocLine(sb.toString());
        field.addJavaDocLine(" *");
        addJavadocTag(field, false);
        field.addJavaDocLine(" */");
    }
 
    public void addFieldComment(Field field, IntrospectedTable introspectedTable) {
        field.addJavaDocLine("/**");
        addJavadocTag(field, false);
        field.addJavaDocLine(" */");
    }
 
    public void addGetterComment(Method method, IntrospectedTable introspectedTable, IntrospectedColumn introspectedColumn) {
        method.addJavaDocLine("/**");
        addJavadocTag(method, false);
        method.addJavaDocLine(" */");
    }
 
    public void addSetterComment(Method method, IntrospectedTable introspectedTable, IntrospectedColumn introspectedColumn) {
        method.addJavaDocLine("/**");
        addJavadocTag(method, false);
        method.addJavaDocLine(" */");
    }
 
    protected void addJavadocTag(JavaElement javaElement, boolean markAsDoNotDelete) {
        StringBuilder sb = new StringBuilder();
        sb.append(" * ");
        sb.append(MergeConstants.NEW_ELEMENT_TAG);
        if (markAsDoNotDelete) {
            sb.append(" do_not_delete_during_merge"); //$NON-NLS-1$
        }
        String s = getDateString();
        if (s != null) {
            sb.append(' ');
            sb.append(s);
        }
        javaElement.addJavaDocLine(sb.toString());
    }
 
    protected String getDateString() {
        return DateFormatUtils.format(new Date(), "yyyy-MM-dd HH:mm:ss");
    }
}

MyBatis的配置文件修改为：

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<commentGenerator type="com.test.mbg.RemarksCommentGenerator">
</commentGenerator>

运行MyBatis生成器

改用自定义的RemarksCommentGenerator后，运行MyBatis插件可能会报错。需要使用Java来运行MyBatis生成器，代码如下 [doc]：

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package com.test.mbg;
 
import java.io.File;
import java.util.ArrayList;
import java.util.List;
 
import org.mybatis.generator.api.MyBatisGenerator;
import org.mybatis.generator.config.Configuration;
import org.mybatis.generator.config.xml.ConfigurationParser;
import org.mybatis.generator.internal.DefaultShellCallback;
 
/**
 *  使用Java运行 MyBatis Generator
 * http://www.mybatis.org/generator/running/runningWithJava.html
 */
public class MyBatisGen {
 
    public static void main(String[] args) throws Exception {
        String fileName = "F:/code/mybatis-generator.xml";
        File configFile = new File(fileName);
        List<String> warnings = new ArrayList<String>();
        boolean overwrite = true;
        ConfigurationParser cp = new ConfigurationParser(warnings);
        Configuration config = cp.parseConfiguration(configFile);
        DefaultShellCallback callback = new DefaultShellCallback(overwrite);
        MyBatisGenerator myBatisGenerator = new MyBatisGenerator(config, callback, warnings);
        myBatisGenerator.generate(null);
    }
}