廖雪峰Java15JDBC编程-3JDBC接口-3JDBC更新

使用update语句的时候，需要通过JDBC实现update语句的执行，这个时候仍然通过PreparedStatement对象来使用，直接传入update语句，然后通过setObject传入占位符的值，最后通过executeUpdate()就可以执行这个update语句。
executeUpdate()返回值是int，代表符合条件的记录数量。

## 1. update
```#java
//update
try(Connection conn = DriverManager.getConnection(JDBC_URL, JDBC_USER, JDBC_PASSWORD)){
try(PreparedStatement ps = conn.prepareStatement("update students set name=? where id=?")){
ps.setObject(1, "Bob");
ps.setObject(2, 999);
ps.executeUpdate();
}
}
```
### 1.1 update修改示例 JdbcUpdate.java
```#java
package com.feiyangedu.sample.pop3;

import java.sql.*;

import java.util.ArrayList;

import java.util.List;

public class JdbcUpdate {

static final String JDBC_URL = "jdbc:mysql://localhost:13306/test0828?useSSL=false&characterEncoding=utf8&serverTimeZone=UTC";

static final String JDBC_USER="root";

static final String JDBC_PASSWORD = "123456";

public static  void main(String[] args) throws SQLException{
    List<Student> students = getAllStudents();
    for(Student student:students){
        System.out.println(student);
    }
    Student std = students.get(0);
    std.classId = new Long(2);
    std.name = "Alice";
    std.gender = "F";
    update(std);
    System.out.println("--变更后--");
    students = getAllStudents();
    for(Student student:students){
        System.out.println(student);
    }
}

static void update(Student std) throws SQLException{
    try(Connection conn = getConnection()){
        try(PreparedStatement ps = conn.prepareStatement("update students set class_id=?,name=?,gender=? where id=?")){
            ps.setObject(1, std.classId);
            ps.setObject(2, std.name);
            ps.setObject(3, std.gender);
            ps.setObject(4, std.id);
            int n = ps.executeUpdate();
            System.out.println(n+"条记录发生变更.");
        }
    }
}
static List<Student> getAllStudents() throws SQLException{
    try(Connection conn = getConnection()){
        try(PreparedStatement ps = conn.prepareStatement("select * from students")){
            ResultSet rs = ps.executeQuery();
            List<Student> list = new ArrayList<>();
            while(rs.next()){
                Long id = rs.getLong("id");
                Long classId = rs.getLong("class_id");
                String name = rs.getString("name");
                String gender = rs.getString("gender");
                Student std = new Student(id,classId,name,gender);
                list.add(std);
            }
            return list;
        }
    }
}
static Connection getConnection() throws SQLException {
    return DriverManager.getConnection(JDBC_URL,JDBC_USER,JDBC_PASSWORD);
}

}

<img src="https://img2018.cnblogs.com/blog/1418970/201909/1418970-20190901102130426-1636009720.png" width="500" />

##    2. delete语句是一样的
```#java
    try(Connection conn = DriverManager.getConnection(JDBC_URL, JDBC_USER, JDBC_PASSWORD)){
        try(PreparedStatement ps = conn.prepareStatement("delete from student where id=?")){
            ps.setObject(1, 999);
            int n = ps.executeUpdate(); //返回结果为删除记录的数量
        }
    }

2.1 delete示例JdbcDelete.java

package com.feiyangedu.sample.pop3;

import java.sql.*;
import java.util.ArrayList;
import java.util.List;

public class JdbcDelete {
    static final String JDBC_URL = "jdbc:mysql://localhost:13306/test0828?useSSL=false&characterEncoding=utf8&serverTimeZone=UTC";
    static final String JDBC_USER="root";
    static final String JDBC_PASSWORD = "123456";
    public static void main(String[] args) throws SQLException{
        List<Student> students = getAllStudents();
        for(Student student:students){
            System.out.println(student);
        }
        long studentId = students.get(students.size()-1).id; //查找最后1条记录的id
        delete(studentId);
        System.out.println(studentId+"删除成功");
        students = getAllStudents();
        for(Student student:students){
            System.out.println(student);
        }
    }
    static void delete(long studentId) throws SQLException{
        try(Connection conn = getConnection()){
            try(PreparedStatement ps = conn.prepareStatement("delete from students where id=?")){
                ps.setObject(1, studentId);
                ps.executeUpdate();
            }
        }
    }
    static List<Student> getAllStudents() throws SQLException {
        try(Connection conn = getConnection()){
            try(PreparedStatement ps = conn.prepareStatement("select * from students")){
                ResultSet rs = ps.executeQuery();
                List<Student> list = new ArrayList<>();
                while(rs.next()){
                    long id = rs.getLong("id");
                    long classId = rs.getLong("class_id");
                    String name = rs.getString("name");
                    String gender = rs.getString("gender");
                    Student std = new Student(id,classId,name,gender);
                    list.add(std);
                }
                return list;
            }
        }
    }
    static Connection getConnection() throws SQLException {
        return DriverManager.getConnection(JDBC_URL,JDBC_USER,JDBC_PASSWORD);
    }
}

3. insert语句

3.1 单纯插入数据

    try(Connection conn = DriverManager.getConnection(JDBC_URL, JDBC_USER, JDBC_PASSWORD)){
        try(PreparedStatement ps = conn.prepareStatement("insert into student(id, class_id, name, gender) values(?, ?, ?, ?)")){
            ps.setObject(1, 999);
            ps.setObject(2, 1);
            ps.setObject(3, "Bob");
            ps.setObject(4, "M");
            int n = ps.executeUpdate();
        }
    }

3.2 插入后获自增的id

    try(Connection conn = DriverManager.getConnection(JDBC_URL, JDBC_USER, JDBC_PASSWORD)){
        try(PreparedStatement ps = conn.prepareStatement("insert into students(class_id, name, gender) values (?, ? ,?)",Statement.RETURN_GENERATED_KEYS)){
            //我们并没有指定id的值，而是由数据库自动生成。我们往往需要获取数据库自动生成主键的值。这就需要再调用preparedStatement的时候传入一个常量Statement.RETURN_GENERATED_KEYS，表示需要返回数据库生成的主键。在执行executeUpdate()方法以后，我们可以通过getGeneratedKeys()获取一个ResultKey对象。这个对象包含了数据库自动生成主键的值，因为我们只有1条插入的数据，因此获得第一条
            ps.setObject(1, 1);
            ps.setObject(2, "Bob");
            ps.setObject(3, "M");
            int n = ps.executeUpdate();
            try(ResultSet rs = ps.getGeneratedKeys()){
                if(rs.next()){
                    long id = rs.getLong(1);
                }
            }
        }
    }

3.3 insert示例代码 JdbcInsert.java

package com.feiyangedu.sample.pop3;

import java.sql.*;
import java.util.ArrayList;
import java.util.List;

public class JdbcInsert {
    static final String JDBC_URL = "jdbc:mysql://localhost:13306/test0828?useSSL=false&characterEncoding=utf8&serverTimeZone=UTC";
    static final String JDBC_USER="root";
    static final String JDBC_PASSWORD = "123456";

    public static  void main(String[] args) throws SQLException {
        List<Student> students = getAllStudents();
        for(Student student:students){
            System.out.println(student);
        }
        insertWithAutoGeneratedId(new Student(2,"Tim","M"));
        insertWithId(new Student(999,2,"Bob","M"));
        System.out.println("插入完成");
        students = getAllStudents();
        for(Student student:students){
            System.out.println(student);
        }
    }

    static void insertWithId(Student std) throws SQLException{
        try(Connection conn = getConnection()){
            try(PreparedStatement ps = conn.prepareStatement("insert into students values (?, ?, ?, ?)")){
                ps.setObject(1, std.id);
                ps.setObject(2, std.classId);
                ps.setObject(3, std.name);
                ps.setObject(4, std.gender);

                int n = ps.executeUpdate();
                System.out.println(n+"条记录被插入");
            }
        }
    }
    static void insertWithAutoGeneratedId(Student std) throws SQLException{
        try(Connection conn = getConnection()){
            try(PreparedStatement ps = conn.prepareStatement("insert into students(class_id, name, gender) values (?, ?, ?)",Statement.RETURN_GENERATED_KEYS)){ //需要返回数据库自动生成主键的值
                ps.setObject(1, std.classId);
                ps.setObject(2, std.name);
                ps.setObject(3, std.gender);
                int n = ps.executeUpdate();
                System.out.println(n+"条记录被插入");
                try(ResultSet rs = ps.getGeneratedKeys()){ //通过getGeneratedKeys()拿到主键
                    if(rs.next()){
                        long id = rs.getLong(1);
                        std.id = id;
                    }
                }
            }
        }
    }
    static List<Student> getAllStudents() throws SQLException{
        try(Connection conn = getConnection()){
            try(PreparedStatement ps = conn.prepareStatement("select * from students")){
                ResultSet rs = ps.executeQuery();
                List<Student> list = new ArrayList<>();
                while(rs.next()){
                    long id = rs.getLong("id");
                    long classId = rs.getLong("class_id");
                    String name = rs.getString("name");
                    String gender = rs.getString("gender");
                    Student std = new Student(id,classId,name,gender);
                    list.add(std);
                }
                return list;
            }
        }
    }
    static Connection getConnection() throws SQLException {
        return DriverManager.getConnection(JDBC_URL,JDBC_USER,JDBC_PASSWORD);
    }

}

4 JDBC更新总结

• 使用PreparedStatement的executeUpdate()进行更新
• 更新操作包括update, insert, delete语句
• 更新结果是int