Mybatis Generator 執行後，我看到在實體類包中出現了四個類。多出來兩個帶 Example 的是什麼呢？
限於篇幅，只研究 Department.java 和 DepartmentExample.java 這兩個就好了，Employee 的估計應該也差不多。

8.1 Department.java

package com.hh.ssm.bean;

import java.util.Date;

public class Department {
    private Integer departmentId;

    private String departmentName;

    private
 
 Date gmtCreate;

    private Date gmtModified;

    public Integer getDepartmentId() {
        return departmentId;
    }

    public void setDepartmentId(Integer departmentId) {
        this.departmentId = departmentId;
    }

    public String getDepartmentName() {
        return departmentName;
    }
    //  看到下面的這個細節，就覺得自己平時不夠細緻了。
 

    public void setDepartmentName(String departmentName) {
        this.departmentName = departmentName == null ? null : departmentName.trim();
    }

    public Date getGmtCreate() {
        return gmtCreate;
    }

    public void setGmtCreate(Date gmtCreate) {
        this.gmtCreate = gmtCreate;
    }

    public
 
 Date getGmtModified() {
        return gmtModified;
    }

    public void setGmtModified(Date gmtModified) {
        this.gmtModified = gmtModified;
    }
}

從上面的程式碼可以得出以下幾點結論：
1. 成員變數與表中的各個列在名稱和資料型別上都能很好的一一對應
2. 而且命名符合小寫駝峰規範
3. 無建構函式，如果需要可以自己新增，但一定不能少了無參建構函式
4. 可以嘗試重寫 toString() 方法

8.2 DepartmentExample.java

這個是 Mybatis Generator 生成的與 Department 實體相關的另一個實體。幹嘛用的呢？我研究一下里面的構成，大體上知道了思路所在。這個類的裡面有一個內部靜態抽象類 GeneratedCriteria ，還有兩個內部靜態類 Criteria 和 Criterion 。

8.2.1 SQL 拼接函式（叫方法感覺怪怪的，用於拼接 SQL 語句的方法？）

可以看見在不涉及成員變數的方法大概有以下幾個：

8.2.2 查詢條件拼接函式（拼接查詢條件的方法）

針對每個成員變數，Mybatis Generator 都提供了個查詢條件的拼接函式。
1. is null
2. not null
3. =
4. <>
5. >
6. >=
7. <
8. <=
9. like
10. not like
11. in
12. not in
13. between
14. not between

package com.hh.ssm.bean;

import java.util.ArrayList;
import java.util.Date;
import java.util.List;

public class DepartmentExample {

    protected String orderByClause; // order by 子句
    protected boolean distinct; // distinct 子句，是否去重複
    protected List<Criteria> oredCriteria; // 所有條件的集合，這些條件的關係是 or
    // 無參建構函式，建立條件 List
    public DepartmentExample() {
        oredCriteria = new ArrayList<Criteria>();
    }
    // getter 和 setter ， oredCriteria 的setter就沒有了，因為在建構函式中已經寫了
    public void setOrderByClause(String orderByClause) {
        this.orderByClause = orderByClause;
    }
    public String getOrderByClause() {
        return orderByClause;
    }
    public void setDistinct(boolean distinct) {
        this.distinct = distinct;
    }
    public boolean isDistinct() {
        return distinct;
    }
    public List<Criteria> getOredCriteria() {
        return oredCriteria;
    }
    // or 方法：向條件集合中增加條件
    public void or(Criteria criteria) {
        oredCriteria.add(criteria);
    }

    public Criteria or() {
        Criteria criteria = createCriteriaInternal();
        oredCriteria.add(criteria);
        return criteria;
    }

    public Criteria createCriteria() {
        Criteria criteria = createCriteriaInternal();
        if (oredCriteria.size() == 0) {
            oredCriteria.add(criteria);
        }
        return criteria;
    }

    protected Criteria createCriteriaInternal() {
        Criteria criteria = new Criteria();
        return criteria;
    }

    public void clear() {
        oredCriteria.clear();
        orderByClause = null;
        distinct = false;
    }

    protected abstract static class GeneratedCriteria {
        protected List<Criterion> criteria;

        protected GeneratedCriteria() {
            super();
            criteria = new ArrayList<Criterion>();
        }

        public boolean isValid() {
            return criteria.size() > 0;
        }

        public List<Criterion> getAllCriteria() {
            return criteria;
        }

        public List<Criterion> getCriteria() {
            return criteria;
        }

        protected void addCriterion(String condition) {
            if (condition == null) {
                throw new RuntimeException("Value for condition cannot be null");
            }
            criteria.add(new Criterion(condition));
        }

        protected void addCriterion(String condition, Object value, String property) {
            if (value == null) {
                throw new RuntimeException("Value for " + property + " cannot be null");
            }
            criteria.add(new Criterion(condition, value));
        }

        protected void addCriterion(String condition, Object value1, Object value2, String property) {
            if (value1 == null || value2 == null) {
                throw new RuntimeException("Between values for " + property + " cannot be null");
            }
            criteria.add(new Criterion(condition, value1, value2));
        }

        public Criteria andDepartmentIdIsNull() {
            addCriterion("department_id is null");
            return (Criteria) this;
        }

        public Criteria andDepartmentIdIsNotNull() {
            addCriterion("department_id is not null");
            return (Criteria) this;
        }

        public Criteria andDepartmentIdEqualTo(Integer value) {
            addCriterion("department_id =", value, "departmentId");
            return (Criteria) this;
        }

        public Criteria andDepartmentIdNotEqualTo(Integer value) {
            addCriterion("department_id <>", value, "departmentId");
            return (Criteria) this;
        }

        public Criteria andDepartmentIdGreaterThan(Integer value) {
            addCriterion("department_id >", value, "departmentId");
            return (Criteria) this;
        }

        public Criteria andDepartmentIdGreaterThanOrEqualTo(Integer value) {
            addCriterion("department_id >=", value, "departmentId");
            return (Criteria) this;
        }

        public Criteria andDepartmentIdLessThan(Integer value) {
            addCriterion("department_id <", value, "departmentId");
            return (Criteria) this;
        }

        public Criteria andDepartmentIdLessThanOrEqualTo(Integer value) {
            addCriterion("department_id <=", value, "departmentId");
            return (Criteria) this;
        }

        public Criteria andDepartmentIdIn(List<Integer> values) {
            addCriterion("department_id in", values, "departmentId");
            return (Criteria) this;
        }

        public Criteria andDepartmentIdNotIn(List<Integer> values) {
            addCriterion("department_id not in", values, "departmentId");
            return (Criteria) this;
        }

        public Criteria andDepartmentIdBetween(Integer value1, Integer value2) {
            addCriterion("department_id between", value1, value2, "departmentId");
            return (Criteria) this;
        }

        public Criteria andDepartmentIdNotBetween(Integer value1, Integer value2) {
            addCriterion("department_id not between", value1, value2, "departmentId");
            return (Criteria) this;
        }

        public Criteria andDepartmentNameIsNull() {
            addCriterion("department_name is null");
            return (Criteria) this;
        }

        public Criteria andDepartmentNameIsNotNull() {
            addCriterion("department_name is not null");
            return (Criteria) this;
        }

        public Criteria andDepartmentNameEqualTo(String value) {
            addCriterion("department_name =", value, "departmentName");
            return (Criteria) this;
        }

        public Criteria andDepartmentNameNotEqualTo(String value) {
            addCriterion("department_name <>", value, "departmentName");
            return (Criteria) this;
        }

        public Criteria andDepartmentNameGreaterThan(String value) {
            addCriterion("department_name >", value, "departmentName");
            return (Criteria) this;
        }

        public Criteria andDepartmentNameGreaterThanOrEqualTo(String value) {
            addCriterion("department_name >=", value, "departmentName");
            return (Criteria) this;
        }

        public Criteria andDepartmentNameLessThan(String value) {
            addCriterion("department_name <", value, "departmentName");
            return (Criteria) this;
        }

        public Criteria andDepartmentNameLessThanOrEqualTo(String value) {
            addCriterion("department_name <=", value, "departmentName");
            return (Criteria) this;
        }

        public Criteria andDepartmentNameLike(String value) {
            addCriterion("department_name like", value, "departmentName");
            return (Criteria) this;
        }

        public Criteria andDepartmentNameNotLike(String value) {
            addCriterion("department_name not like", value, "departmentName");
            return (Criteria) this;
        }

        public Criteria andDepartmentNameIn(List<String> values) {
            addCriterion("department_name in", values, "departmentName");
            return (Criteria) this;
        }

        public Criteria andDepartmentNameNotIn(List<String> values) {
            addCriterion("department_name not in", values, "departmentName");
            return (Criteria) this;
        }

        public Criteria andDepartmentNameBetween(String value1, String value2) {
            addCriterion("department_name between", value1, value2, "departmentName");
            return (Criteria) this;
        }

        public Criteria andDepartmentNameNotBetween(String value1, String value2) {
            addCriterion("department_name not between", value1, value2, "departmentName");
            return (Criteria) this;
        }

        public Criteria andGmtCreateIsNull() {
            addCriterion("gmt_create is null");
            return (Criteria) this;
        }

        public Criteria andGmtCreateIsNotNull() {
            addCriterion("gmt_create is not null");
            return (Criteria) this;
        }

        public Criteria andGmtCreateEqualTo(Date value) {
            addCriterion("gmt_create =", value, "gmtCreate");
            return (Criteria) this;
        }

        public Criteria andGmtCreateNotEqualTo(Date value) {
            addCriterion("gmt_create <>", value, "gmtCreate");
            return (Criteria) this;
        }

        public Criteria andGmtCreateGreaterThan(Date value) {
            addCriterion("gmt_create >", value, "gmtCreate");
            return (Criteria) this;
        }

        public Criteria andGmtCreateGreaterThanOrEqualTo(Date value) {
            addCriterion("gmt_create >=", value, "gmtCreate");
            return (Criteria) this;
        }

        public Criteria andGmtCreateLessThan(Date value) {
            addCriterion("gmt_create <", value, "gmtCreate");
            return (Criteria) this;
        }

        public Criteria andGmtCreateLessThanOrEqualTo(Date value) {
            addCriterion("gmt_create <=", value, "gmtCreate");
            return (Criteria) this;
        }

        public Criteria andGmtCreateIn(List<Date> values) {
            addCriterion("gmt_create in", values, "gmtCreate");
            return (Criteria) this;
        }

        public Criteria andGmtCreateNotIn(List<Date> values) {
            addCriterion("gmt_create not in", values, "gmtCreate");
            return (Criteria) this;
        }

        public Criteria andGmtCreateBetween(Date value1, Date value2) {
            addCriterion("gmt_create between", value1, value2, "gmtCreate");
            return (Criteria) this;
        }

        public Criteria andGmtCreateNotBetween(Date value1, Date value2) {
            addCriterion("gmt_create not between", value1, value2, "gmtCreate");
            return (Criteria) this;
        }

        public Criteria andGmtModifiedIsNull() {
            addCriterion("gmt_modified is null");
            return (Criteria) this;
        }

        public Criteria andGmtModifiedIsNotNull() {
            addCriterion("gmt_modified is not null");
            return (Criteria) this;
        }

        public Criteria andGmtModifiedEqualTo(Date value) {
            addCriterion("gmt_modified =", value, "gmtModified");
            return (Criteria) this;
        }

        public Criteria andGmtModifiedNotEqualTo(Date value) {
            addCriterion("gmt_modified <>", value, "gmtModified");
            return (Criteria) this;
        }

        public Criteria andGmtModifiedGreaterThan(Date value) {
            addCriterion("gmt_modified >", value, "gmtModified");
            return (Criteria) this;
        }

        public Criteria andGmtModifiedGreaterThanOrEqualTo(Date value) {
            addCriterion("gmt_modified >=", value, "gmtModified");
            return (Criteria) this;
        }

        public Criteria andGmtModifiedLessThan(Date value) {
            addCriterion("gmt_modified <", value, "gmtModified");
            return (Criteria) this;
        }

        public Criteria andGmtModifiedLessThanOrEqualTo(Date value) {
            addCriterion("gmt_modified <=", value, "gmtModified");
            return (Criteria) this;
        }

        public Criteria andGmtModifiedIn(List<Date> values) {
            addCriterion("gmt_modified in", values, "gmtModified");
            return (Criteria) this;
        }

        public Criteria andGmtModifiedNotIn(List<Date> values) {
            addCriterion("gmt_modified not in", values, "gmtModified");
            return (Criteria) this;
        }

        public Criteria andGmtModifiedBetween(Date value1, Date value2) {
            addCriterion("gmt_modified between", value1, value2, "gmtModified");
            return (Criteria) this;
        }

        public Criteria andGmtModifiedNotBetween(Date value1, Date value2) {
            addCriterion("gmt_modified not between", value1, value2, "gmtModified");
            return (Criteria) this;
        }
    }

    public static class Criteria extends GeneratedCriteria {

        protected Criteria() {
            super();
        }
    }

    public static class Criterion {
        private String condition;

        private Object value;

        private Object secondValue;

        private boolean noValue;

        private boolean singleValue;

        private boolean betweenValue;

        private boolean listValue;

        private String typeHandler;

        public String getCondition() {
            return condition;
        }

        public Object getValue() {
            return value;
        }

        public Object getSecondValue() {
            return secondValue;
        }

        public boolean isNoValue() {
            return noValue;
        }

        public boolean isSingleValue() {
            return singleValue;
        }

        public boolean isBetweenValue() {
            return betweenValue;
        }

        public boolean isListValue() {
            return listValue;
        }

        public String getTypeHandler() {
            return typeHandler;
        }

        protected Criterion(String condition) {
            super();
            this.condition = condition;
            this.typeHandler = null;
            this.noValue = true;
        }

        protected Criterion(String condition, Object value, String typeHandler) {
            super();
            this.condition = condition;
            this.value = value;
            this.typeHandler = typeHandler;
            if (value instanceof List<?>) {
                this.listValue = true;
            } else {
                this.singleValue = true;
            }
        }

        protected Criterion(String condition, Object value) {
            this(condition, value, null);
        }

        protected Criterion(String condition, Object value, Object secondValue, String typeHandler) {
            super();
            this.condition = condition;
            this.value = value;
            this.secondValue = secondValue;
            this.typeHandler = typeHandler;
            this.betweenValue = true;
        }

        protected Criterion(String condition, Object value, Object secondValue) {
            this(condition, value, secondValue, null);
        }
    }
}