mybatis定义自己的mapper和xml

用Mybatis generator可以自动生成table对应的javaBean和xml,mapper接口。由于表的结构会发生变化，而业务中生成的mapper并不能完全满足需求，因此要自己写sql xml, 不能写在mybatis 生成的文件中，不然下次就会被覆盖了。

解决办法：
1:建自己的Mapper.java接口,目录和mybatis生成的mapper.java相同。先不定义方法
2:见一个自己的mapper xml，和mybatis生成的mapper xml放在一个目录即可。 namespace写自己Mapper.java的全类名，然后写<select>，这里引用mybatis生成的mapper.xml中的Base_Column_List和BaseResultMap，只要写全名即可，就是：com.xxx.xx.XxxMapper.Base_Column_List和com.xxx.xx.XxxMapper.BaseResultMap.
3:补充Mapper java中方法，方法名和<select>的id相同。



PS:
自定义的Mapper.xml和Mapper.java可以不和mybatis自动生成的在一个目录。

mybatis-generator默认是不产生分页语句的。需要加个插件。
参考：http://www.cnblogs.com/iamcui/p/4788910.html
https://github.com/reedF/rmi-demo/blob/master/src/main/java/org/mybatis/generator/plugin/PaginationMysqlPlugin.java

import java.util.List;
import org.mybatis.generator.api.CommentGenerator;
import org.mybatis.generator.api.IntrospectedTable;
import org.mybatis.generator.api.PluginAdapter;
import org.mybatis.generator.api.ShellRunner;
import org.mybatis.generator.api.dom.java.Field;
import org.mybatis.generator.api.dom.java.FullyQualifiedJavaType;
import org.mybatis.generator.api.dom.java.JavaVisibility;
import org.mybatis.generator.api.dom.java.Method;
import org.mybatis.generator.api.dom.java.Parameter;
import org.mybatis.generator.api.dom.java.TopLevelClass;
import org.mybatis.generator.api.dom.xml.Attribute;
import org.mybatis.generator.api.dom.xml.TextElement;
import org.mybatis.generator.api.dom.xml.XmlElement;

/**
 * <pre>
 * add pagination using mysql limit. 
 * This class is only used in ibator code generator.
 * </pre>
 */
public class PaginationMysqlPlugin extends PluginAdapter {
    @Override
    public boolean modelExampleClassGenerated(TopLevelClass topLevelClass,
            IntrospectedTable introspectedTable) {
        // add field, getter, setter for limit clause
        addLimit(topLevelClass, introspectedTable, "offset");
        addLimit(topLevelClass, introspectedTable, "limit");
        return super.modelExampleClassGenerated(topLevelClass,
                introspectedTable);
    }

    @Override
    public boolean sqlMapSelectByExampleWithoutBLOBsElementGenerated(
            XmlElement element, IntrospectedTable introspectedTable) {
        // XmlElement isParameterPresenteElemen = (XmlElement) element
        // .getElements().get(element.getElements().size() - 1);
//        XmlElement isNotNullElement = new XmlElement("isGreaterEqual"); //$NON-NLS-1$  
//        isNotNullElement.addAttribute(new Attribute("property", "limitStart")); //$NON-NLS-1$ //$NON-NLS-2$  
//        isNotNullElement.addAttribute(new Attribute("compareValue", "0")); //$NON-NLS-1$ //$NON-NLS-2$  
        
        XmlElement isNotNullElement = new XmlElement("if");  
        isNotNullElement.addAttribute(new Attribute("test", "limit >= 0"));
        isNotNullElement.addElement(new TextElement(
                " limit ${offset} , ${limit}"));
        // isParameterPresenteElemen.addElement(isNotNullElement);
        element.addElement(isNotNullElement);
        return super.sqlMapUpdateByExampleWithoutBLOBsElementGenerated(element,
                introspectedTable);
    }

    private void addLimit(TopLevelClass topLevelClass,
            IntrospectedTable introspectedTable, String name) {
        CommentGenerator commentGenerator = context.getCommentGenerator();
        Field field = new Field();
        field.setVisibility(JavaVisibility.PROTECTED);
        field.setType(FullyQualifiedJavaType.getIntInstance());
        field.setName(name);
        field.setInitializationString("-1");
        commentGenerator.addFieldComment(field, introspectedTable);
        topLevelClass.addField(field);
        char c = name.charAt(0);
        String camel = Character.toUpperCase(c) + name.substring(1);
        Method method = new Method();
        method.setVisibility(JavaVisibility.PUBLIC);
        method.setName("set" + camel);
        method.addParameter(new Parameter(FullyQualifiedJavaType
                .getIntInstance(), name));
        method.addBodyLine("this." + name + "=" + name + ";");
        commentGenerator.addGeneralMethodComment(method, introspectedTable);
        topLevelClass.addMethod(method);
        method = new Method();
        method.setVisibility(JavaVisibility.PUBLIC);
        method.setReturnType(FullyQualifiedJavaType.getIntInstance());
        method.setName("get" + camel);
        method.addBodyLine("return " + name + ";");
        commentGenerator.addGeneralMethodComment(method, introspectedTable);
        topLevelClass.addMethod(method);
    }

    /**
     * This plugin is always valid - no properties are required
     */
    public boolean validate(List<String> warnings) {
        return true;
    }

    public static void generate() {
        String config = PaginationMysqlPlugin.class.getClassLoader()
                .getResource("generatorConfig.xml").getFile();
        String[] arg = { "-configfile", config, "-overwrite" };
        ShellRunner.main(arg);
    }

    public static void main(String[] args) {
        generate();
    }
}

原代码是用limitStart和limitEnd2个参数，不符合正常习惯，这里改成offset和limit.
注意offset参数不能为空。