概述：
Mybatis中的延迟加载，也称为懒加载，是指设置表的关联查询时，按照设置表的延迟规则推迟对关联对象的select查询。例如在进行一对多的关联查询时，之查询出一方，当程序需要多方数据时。Mybatis再发出sql进行查询。这样以来，延迟加载就可以减轻数据库的压力。Mybatis的延迟加载，只是对关联对象的延迟设置，对于主加载对象都是直接执行查询语句进行查询的。
一.加载时机
1.直接加载：
执行完之加载对象的select语句后，直接对关联对象的select进行查询。
2.侵入式延迟：
执行主对象的查询时，不会执行对关联对象的查询。当程序访问之加载对象的详情属性时，立即进行对关联对象的select查询。
3.深度延迟：
执行主对象的查询时，不会执行对关联对象的查询。当程序访问之加载对象的详情属性时，也不会进行对关联对象的select查询。当访问关联对象的详情时，才会执行对关联对象进行select查询。
侵入式延迟加载的配置方法：
1.编写mybatis_config.xml大配置文件
2.实体类：
1 package com.wdy.entity;
2
3 import javax.persistence.*;
4 import java.sql.Timestamp;
5 import java.util.List;
6
7
8 public class SmbmsRole {
9 private Integer id;
10 private String roleCode;
11 private String roleName;
12 private Long createdBy;
13 private Timestamp creationDate;
14
15 public SmbmsRole() {
16 }
17
18 @Override
19 public String toString() {
20 return "SmbmsRole{" +
21 "id=" + id +
22 ", roleCode='" + roleCode + '\'' +
23 ", roleName='" + roleName + '\'' +
24 ", createdBy=" + createdBy +
25 ", creationDate=" + creationDate +
26 ", users=" + users +
27 ", modifyBy=" + modifyBy +
28 ", modifyDate=" + modifyDate +
29 '}';
30 }
31
32 private List<SmbmsUser> users;
33
34 public SmbmsRole(Integer id, String roleCode, String roleName, Long createdBy, Timestamp creationDate, List<SmbmsUser> users, Long modifyBy, Timestamp modifyDate) {
35 this.id = id;
36 this.roleCode = roleCode;
37 this.roleName = roleName;
38 this.createdBy = createdBy;
39 this.creationDate = creationDate;
40 this.users = users;
41 this.modifyBy = modifyBy;
42 this.modifyDate = modifyDate;
43 }
44
45 private Long modifyBy;
46
47 public Integer getId() {
48 return id;
49 }
50
51 public void setId(Integer id) {
52 this.id = id;
53 }
54
55 public String getRoleCode() {
56 return roleCode;
57 }
58
59 public void setRoleCode(String roleCode) {
60 this.roleCode = roleCode;
61 }
62
63 public String getRoleName() {
64 return roleName;
65 }
66
67 public void setRoleName(String roleName) {
68 this.roleName = roleName;
69 }
70
71 public Long getCreatedBy() {
72 return createdBy;
73 }
74
75 public void setCreatedBy(Long createdBy) {
76 this.createdBy = createdBy;
77 }
78
79 public Timestamp getCreationDate() {
80 return creationDate;
81 }
82
83 public void setCreationDate(Timestamp creationDate) {
84 this.creationDate = creationDate;
85 }
86
87 public List<SmbmsUser> getUsers() {
88 return users;
89 }
90
91 public void setUsers(List<SmbmsUser> users) {
92 this.users = users;
93 }
94
95 public Long getModifyBy() {
96 return modifyBy;
97 }
98
99 public void setModifyBy(Long modifyBy) {
100 this.modifyBy = modifyBy;
101 }
102
103 public Timestamp getModifyDate() {
104 return modifyDate;
105 }
106
107 public void setModifyDate(Timestamp modifyDate) {
108 this.modifyDate = modifyDate;
109 }
110
111 private Timestamp modifyDate;
112
113 }
User实体类：
1 package com.wdy.entity; 2 3 import javax.persistence.*; 4 import java.sql.Date; 5 import java.sql.Timestamp; 6 import java.util.List; 7 8 9 public class SmbmsUser { 10 private Integer id; 11 private String userCode; 12 private String userName; 13 private String userPassword; 14 private Integer gender; 15 private Date birthday; 16 private String phone; 17 private String address; 18 private Integer userRole; 19 private Long createdBy; 20 21 @Override 22 public String toString() { 23 return "SmbmsUser{" + 24 "id=" + id + 25 ", userCode='" + userCode + '\'' + 26 ", userName='" + userName + '\'' + 27 ", userPassword='" + userPassword + '\'' + 28 ", gender=" + gender + 29 ", birthday=" + birthday + 30 ", phone='" + phone + '\'' + 31 ", address='" + address + '\'' + 32 ", userRole=" + userRole + 33 ", createdBy=" + createdBy + 34 ", creationDate=" + creationDate + 35 ", modifyBy=" + modifyBy + 36 ", modifyDate=" + modifyDate + 37 ", rolesList=" + rolesList + 38 '}'; 39 } 40 41 private Timestamp creationDate; 42 43 public SmbmsUser(Integer id, String userCode, String userName, String userPassword, Integer gender, Date birthday, String phone, String address, Integer userRole, Long createdBy, Timestamp creationDate, Long modifyBy, Timestamp modifyDate, List<SmbmsRole> rolesList) { 44 this.id = id; 45 this.userCode = userCode; 46 this.userName = userName; 47 this.userPassword = userPassword; 48 this.gender = gender; 49 this.birthday = birthday; 50 this.phone = phone; 51 this.address = address; 52 this.userRole = userRole; 53 this.createdBy = createdBy; 54 this.creationDate = creationDate; 55 this.modifyBy = modifyBy; 56 this.modifyDate = modifyDate; 57 this.rolesList = rolesList; 58 } 59 60 private Long modifyBy; 61 62 public SmbmsUser() { 63 } 64 65 private Timestamp modifyDate; 66 67 public Integer getId() { 68 return id; 69 } 70 71 public void setId(Integer id) { 72 this.id = id; 73 } 74 75 public String getUserCode() { 76 return userCode; 77 } 78 79 public void setUserCode(String userCode) { 80 this.userCode = userCode; 81 } 82 83 public String getUserName() { 84 return userName; 85 } 86 87 public void setUserName(String userName) { 88 this.userName = userName; 89 } 90 91 public String getUserPassword() { 92 return userPassword; 93 } 94 95 public void setUserPassword(String userPassword) { 96 this.userPassword = userPassword; 97 } 98 99 public Integer getGender() {100 return gender;101 }102 103 public void setGender(Integer gender) {104 this.gender = gender;105 }106 107 public Date getBirthday() {108 return birthday;109 }110 111 public void setBirthday(Date birthday) {112 this.birthday = birthday;113 }114 115 public String getPhone() {116 return phone;117 }118 119 public void setPhone(String phone) {120 this.phone = phone;121 }122 123 public String getAddress() {124 return address;125 }126 127 public void setAddress(String address) {128 this.address = address;129 }130 131 public Integer getUserRole() {132 return userRole;133 }134 135 public void setUserRole(Integer userRole) {136 this.userRole = userRole;137 }138 139 public Long getCreatedBy() {140 return createdBy;141 }142 143 public void setCreatedBy(Long createdBy) {144 this.createdBy = createdBy;145 }146 147 public Timestamp getCreationDate() {148 return creationDate;149 }150 151 public void setCreationDate(Timestamp creationDate) {152 this.creationDate = creationDate;153 }154 155 public Long getModifyBy() {156 return modifyBy;157 }158 159 public void setModifyBy(Long modifyBy) {160 this.modifyBy = modifyBy;161 }162 163 public Timestamp getModifyDate() {164 return modifyDate;165 }166 167 public void setModifyDate(Timestamp modifyDate) {168 this.modifyDate = modifyDate;169 }170 171 public List<SmbmsRole> getRolesList() {172 return rolesList;173 }174 175 public void setRolesList(List<SmbmsRole> rolesList) {176 this.rolesList = rolesList;177 }178 179 private List<SmbmsRole> rolesList;180 181 182 }